Re: [PATCH v3 2/4] dmaengine: add driver for Samsung s3c24xx SoCs

[Tomasz Figa]

Hi Heiko,

First of all, big thanks for you work on this, letting our dream about 
getting rid of S3C DMA API get closer to the reality. ;)

Overall the driver looks very good, but let me share some comments inline.

On Wednesday 28 of August 2013 00:13:51 Heiko Stübner wrote:
> This adds a new driver to support the s3c24xx dma using the dmaengine
> and makes the old one in mach-s3c24xx obsolete in the long run.
> 
> Conceptually the s3c24xx-dma feels like a distant relative of the pl08x
> with numerous virtual channels being mapped to a lot less physical ones.
> The driver therefore borrows a lot from the amba-pl08x driver in this
> regard. Functionality-wise the driver gains a memcpy ability in
> addition to the slave_sg one.
> 
> The driver supports both the method for requesting the peripheral used
> by SoCs before the S3C2443 and the different method for S3C2443 and
> later.
> 
> On earlier SoCs the hardware channels usable for specific peripherals is
> constrainted while on later SoCs all channels can be used for any
> peripheral.
> 
> Tested on a s3c2416-based board, memcpy using the dmatest module and
> slave_sg partially using the spi-s3c64xx driver.
> 
> Signed-off-by: Heiko Stuebner <heiko@xxxxxxxxx>
> Acked-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
> changes since v2:
> - add missing channel validation in s3c24xx_dma_phy_free when
> repurposing a physical channel for another virtual channel
> - address comments from Vinod Koul:
>   - fix naming of constants to prevent conflicts
>   - better handle the unlikely case of an interrupt happening on an
>     unused channel
> 
> changes since v1:
> - address comments from Linus Walleij
> - support sg-lists with more than 1 element
> - add support for earlier s3c24xx SoCs
> - redo the channeldata definitions:
>   - no need for static ids for the virtual channels
>   - provide a way to encode constraints for earlier variants
>   - better base for later dt bindings
> 
>  drivers/dma/Kconfig                       |   12 +
>  drivers/dma/Makefile                      |    1 +
>  drivers/dma/s3c24xx-dma.c                 | 1285
> +++++++++++++++++++++++++++++ include/linux/platform_data/dma-s3c24xx.h
> |   43 +
>  4 files changed, 1341 insertions(+)
>  create mode 100644 drivers/dma/s3c24xx-dma.c
>  create mode 100644 include/linux/platform_data/dma-s3c24xx.h
> 
> diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
> index 6825957..9f17c27 100644
> --- a/drivers/dma/Kconfig
> +++ b/drivers/dma/Kconfig
> @@ -154,6 +154,18 @@ config TEGRA20_APB_DMA
>  	  This DMA controller transfers data from memory to peripheral 
fifo
>  	  or vice versa. It does not support memory to memory data 
transfer.
> 
> +config S3C24XX_DMAC
> +	bool "Samsung S3C24XX DMA support"
> +	depends on ARCH_S3C24XX && !S3C24XX_DMA
> +	select DMA_ENGINE
> +	select DMA_VIRTUAL_CHANNELS
> +	help
> +	  Support for the Samsung S3C24XX DMA controller driver. The
> +	  DMA controller is having multiple DMA channels which can be
> +	  configured for different peripherals like audio, UART, SPI.
> +	  The DMA controller can transfer data from memory to peripheral,
> +	  periphal to memory, periphal to periphal and memory to memory.
> +
>  source "drivers/dma/sh/Kconfig"
> 
>  config COH901318
> diff --git a/drivers/dma/Makefile b/drivers/dma/Makefile
> index 5e0f2ef..5c1655a 100644
> --- a/drivers/dma/Makefile
> +++ b/drivers/dma/Makefile
> @@ -30,6 +30,7 @@ obj-$(CONFIG_SIRF_DMA) += sirf-dma.o
>  obj-$(CONFIG_TI_EDMA) += edma.o
>  obj-$(CONFIG_STE_DMA40) += ste_dma40.o ste_dma40_ll.o
>  obj-$(CONFIG_TEGRA20_APB_DMA) += tegra20-apb-dma.o
> +obj-$(CONFIG_S3C24XX_DMAC) += s3c24xx-dma.o
>  obj-$(CONFIG_PL330_DMA) += pl330.o
>  obj-$(CONFIG_PCH_DMA) += pch_dma.o
>  obj-$(CONFIG_AMBA_PL08X) += amba-pl08x.o
> diff --git a/drivers/dma/s3c24xx-dma.c b/drivers/dma/s3c24xx-dma.c
> new file mode 100644
> index 0000000..66cd20b
> --- /dev/null
> +++ b/drivers/dma/s3c24xx-dma.c
> @@ -0,0 +1,1285 @@
> +/*
> + * S3C24XX DMA handling
> + *
> + * Copyright (c) 2013 Heiko Stuebner <heiko@xxxxxxxxx>
> + *
> + * based on amba-pl08x.c
> + *
> + * Copyright (c) 2006 ARM Ltd.
> + * Copyright (c) 2010 ST-Ericsson SA
> + *
> + * Author: Peter Pearse <peter.pearse@xxxxxxx>
> + * Author: Linus Walleij <linus.walleij@xxxxxxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or modify
> it + * under the terms of the GNU General Public License as published
> by the Free + * Software Foundation; either version 2 of the License,
> or (at your option) + * any later version.
> + *
> + * The DMA controllers in S3C24XX SoCs have a varying number of DMA
> signals + * that can be routed to any of the 4 to 8 hardware-channels.
> + *
> + * Therefore on these DMA controllers the number of channels
> + * and the number of incoming DMA signals are two totally different
> things. + * It is usually not possible to theoretically handle all
> physical signals, + * so a multiplexing scheme with possible denial of
> use is necessary. + *
> + * Open items:
> + * - bursts
> + */
> +
> +#include <linux/platform_device.h>
> +#include <linux/types.h>
> +#include <linux/dmaengine.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/interrupt.h>
> +#include <linux/clk.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/platform_data/dma-s3c24xx.h>
> +
> +#include "dmaengine.h"
> +#include "virt-dma.h"
> +
> +#define MAX_DMA_CHANNELS	8
> +
> +#define S3C24XX_DISRC			(0x00)
> +#define S3C24XX_DISRCC			(0x04)

nit: You don't have to use parentheses for simple numbers.

> +#define S3C24XX_DISRCC_INC_INCREMENT	(0 << 0)
> +#define S3C24XX_DISRCC_INC_FIXED	(1 << 0)

nit: You could use BIT() macro to define bits.

> +#define S3C24XX_DISRCC_LOC_AHB		(0 << 1)
> +#define S3C24XX_DISRCC_LOC_APB		(1 << 1)
> +
> +#define S3C24XX_DIDST			(0x08)
> +#define S3C24XX_DIDSTC			(0x0C)

nit: Lower case is prefered for hex numbers.

> +#define S3C24XX_DIDSTC_INC_INCREMENT	(0 << 0)
> +#define S3C24XX_DIDSTC_INC_FIXED	(1 << 0)
> +#define S3C24XX_DIDSTC_LOC_AHB		(0 << 1)
> +#define S3C24XX_DIDSTC_LOC_APB		(1 << 1)
> +#define S3C24XX_DIDSTC_INT_TC0		(0 << 2)
> +#define S3C24XX_DIDSTC_INT_RELOAD	(1 << 2)
> +
> +#define S3C24XX_DCON			(0x10)
> +
> +#define S3C24XX_DCON_TC_MASK		0xfffff
> +#define S3C24XX_DCON_DSZ_BYTE		(0 << 20)
> +#define S3C24XX_DCON_DSZ_HALFWORD	(1 << 20)
> +#define S3C24XX_DCON_DSZ_WORD		(2 << 20)
> +#define S3C24XX_DCON_DSZ_MASK		(3 << 20)
> +#define S3C24XX_DCON_DSZ_SHIFT		20
> +#define S3C24XX_DCON_AUTORELOAD		(0 << 22)
> +#define S3C24XX_DCON_NORELOAD		(1 << 22)
> +#define S3C24XX_DCON_HWTRIG		(1 << 23)
> +#define S3C24XX_DCON_HWSRC_SHIFT	24
> +#define S3C24XX_DCON_SERV_SINGLE	(0 << 27)
> +#define S3C24XX_DCON_SERV_WHOLE		(1 << 27)
> +#define S3C24XX_DCON_TSZ_UNIT		(0 << 28)
> +#define S3C24XX_DCON_TSZ_BURST4		(1 << 28)
> +#define S3C24XX_DCON_INT		(1 << 29)
> +#define S3C24XX_DCON_SYNC_PCLK		(0 << 30)
> +#define S3C24XX_DCON_SYNC_HCLK		(1 << 30)
> +#define S3C24XX_DCON_DEMAND		(0 << 31)
> +#define S3C24XX_DCON_HANDSHAKE		(1 << 31)
> +
> +#define S3C24XX_DSTAT			(0x14)
> +#define S3C24XX_DSTAT_STAT_BUSY		(1 << 20)
> +#define S3C24XX_DSTAT_CURRTC_MASK	0xfffff
> +
> +#define S3C24XX_DMASKTRIG		(0x20)
> +#define S3C24XX_DMASKTRIG_STOP		(1 << 2)
> +#define S3C24XX_DMASKTRIG_ON		(1 << 1)
> +#define S3C24XX_DMASKTRIG_SWTRIG	(1 << 0)
> +
> +#define S3C24XX_DMAREQSEL		(0x24)
> +#define S3C24XX_DMAREQSEL_HW		(1 << 0)
> +
> +/*
> + * S3C2410, S3C2440 and S3C2442 SoCs cannot select any physical channel
> + * for a DMA source. Instead only specific channels are valid. + * All
> of these SoCs have 4 physical channels and the number of request + *
> source bits is 3. Additionally we also need 1 bit to mark the channel +
> * as valid.
> + * Therefore we separate the chansel element of the channel data into 4
> + * parts of 4 bits each, to hold the information if the channel is
> valid + * and the hw request source to use.
> + *
> + * Example:
> + * SDI is valid on channels 0, 2 and 3 - with varying hw request
> sources. + * For it the chansel field would look like
> + *
> + * ((BIT(3) | 1) << 3 * 4) | // channel 3, with request source 1
> + * ((BIT(3) | 2) << 2 * 4) | // channel 2, with request source 2
> + * ((BIT(3) | 2) << 0 * 4)   // channel 0, with request source 2
> + */
> +#define S3C24XX_CHANSEL_WIDTH		4
> +#define S3C24XX_CHANSEL_VALID		BIT(3)
> +#define S3C24XX_CHANSEL_REQ_MASK	7
> +
> +/*
> + * struct soc_data - vendor-specific config parameters for individual
> SoCs + * @stride: spacing between the registers of each channel
> + * @has_reqsel: does the controller use the newer requestselection
> mechanism + * @has_clocks: are controllable dma-clocks present
> + */
> +struct soc_data {
> +	int stride;
> +	bool has_reqsel;
> +	bool has_clocks;
> +};
> +
> +/*
> + * enum s3c24xx_dma_chan_state - holds the virtual channel states
> + * @S3C24XX_DMA_CHAN_IDLE: the channel is idle
> + * @S3C24XX_DMA_CHAN_RUNNING: the channel has allocated a physical
> transport + * channel and is running a transfer on it
> + * @S3C24XX_DMA_CHAN_WAITING: the channel is waiting for a physical
> transport + * channel to become available (only pertains to memcpy
> channels) + */
> +enum s3c24xx_dma_chan_state {
> +	S3C24XX_DMA_CHAN_IDLE,
> +	S3C24XX_DMA_CHAN_RUNNING,
> +	S3C24XX_DMA_CHAN_WAITING,
> +};
> +
> +/*
> + * struct s3c24xx_sg - structure containing data per sg
> + * @src_addr: src address of sg
> + * @dst_addr: dst address of sg
> + * @len: transfer len in bytes
> + * @node: node for txd's dsg_list
> + */
> +struct s3c24xx_sg {
> +	dma_addr_t src_addr;
> +	dma_addr_t dst_addr;
> +	size_t len;
> +	struct list_head node;
> +};
> +
> +/*
> + * struct s3c24xx_txd - wrapper for struct dma_async_tx_descriptor
> + * @vd: virtual DMA descriptor
> + * @dsg_list: list of children sg's
> + * @at: sg currently being transfered
> + * @width: transfer width
> + * @disrcc: value for source control register
> + * @didstc: value for destination control register
> + * @dcon: base value for dcon register
> + */
> +struct s3c24xx_txd {
> +	struct virt_dma_desc vd;
> +	struct list_head dsg_list;
> +	struct list_head *at;
> +	u8 width;
> +	u32 disrcc;
> +	u32 didstc;
> +	u32 dcon;
> +};
> +
> +struct s3c24xx_dma_chan;
> +
> +/*
> + * struct s3c24xx_dma_phy - holder for the physical channels
> + * @id: physical index to this channel
> + * @valid: does the channel have all required elements
> + * @base: virtual memory base (remapped) for the this channel
> + * @irq: interrupt for this channel
> + * @clk: clock for this channel
> + * @lock: a lock to use when altering an instance of this struct
> + * @serving: virtual channel currently being served by this
> physicalchannel + * @host: a pointer to the host (internal use)
> + */
> +struct s3c24xx_dma_phy {
> +	unsigned int			id;
> +	bool				valid;
> +	void __iomem			*base;
> +	unsigned int			irq;
> +	struct clk			*clk;
> +	spinlock_t			lock;
> +	struct s3c24xx_dma_chan		*serving;
> +	struct s3c24xx_dma_engine	*host;
> +};
> +
> +/*
> + * struct s3c24xx_dma_chan - this structure wraps a DMA ENGINE channel
> + * @id: the id of the channel
> + * @name: name of the channel
> + * @vc: wrappped virtual channel
> + * @phy: the physical channel utilized by this channel, if there is one
> + * @runtime_addr: address for RX/TX according to the runtime config +
> * @at: active transaction on this channel
> + * @lock: a lock for this channel data
> + * @host: a pointer to the host (internal use)
> + * @state: whether the channel is idle, running etc
> + * @slave: whether this channel is a device (slave) or for memcpy
> + */
> +struct s3c24xx_dma_chan {
> +	int id;
> +	const char *name;
> +	struct virt_dma_chan vc;
> +	struct s3c24xx_dma_phy *phy;
> +	struct dma_slave_config cfg;
> +	struct s3c24xx_txd *at;
> +	struct s3c24xx_dma_engine *host;
> +	enum s3c24xx_dma_chan_state state;
> +	bool slave;
> +};
> +
> +/*
> + * struct s3c24xx_dma_engine - the local state holder for the S3C24XX
> + * @pdev: the corresponding platform device
> + * @pdata: platform data passed in from the platform/machine
> + * @base: virtual memory base (remapped)
> + * @slave: slave engine for this instance
> + * @memcpy: memcpy engine for this instance
> + * @phy_chans: array of data for the physical channels
> + */
> +struct s3c24xx_dma_engine {
> +	struct platform_device			*pdev;
> +	const struct s3c24xx_dma_platdata	*pdata;
> +	struct soc_data				*sdata;
> +	void __iomem				*base;
> +	struct dma_device			slave;
> +	struct dma_device			memcpy;
> +	struct s3c24xx_dma_phy			*phy_chans;
> +};
> +
> +/*
> + * Physical channel handling
> + */
> +
> +/*
> + * Check whether a certain channel is busy or not.
> + */
> +static int s3c24xx_dma_phy_busy(struct s3c24xx_dma_phy *phy)
> +{
> +	unsigned int val = readl(phy->base + S3C24XX_DSTAT);
> +	return val & S3C24XX_DSTAT_STAT_BUSY;
> +}
> +
> +static bool s3c24xx_dma_phy_valid(struct s3c24xx_dma_chan *s3cchan,
> +				  struct s3c24xx_dma_phy *phy)
> +{
> +	struct s3c24xx_dma_engine *s3cdma = s3cchan->host;
> +	const struct s3c24xx_dma_platdata *pdata = s3cdma->pdata;
> +	struct s3c24xx_dma_channel *cdata = &pdata->channels[s3cchan->id];
> +	int phyvalid;
> +
> +	/* every phy is valid for memcopy channels */
> +	if (!s3cchan->slave)
> +		return true;
> +
> +	/* On newer variants all phys can be used for all virtual channels 
*/
> +	if (s3cdma->sdata->has_reqsel)
> +		return true;
> +
> +	phyvalid = (cdata->chansel >> (phy->id * S3C24XX_CHANSEL_WIDTH));
> +	return (phyvalid & S3C24XX_CHANSEL_VALID) ? true : false;
> +}
> +
> +/*
> + * Allocate a physical channel for a virtual channel
> + *
> + * Try to locate a physical channel to be used for this transfer. If
> all + * are taken return NULL and the requester will have to cope by
> using + * some fallback PIO mode or retrying later.
> + */
> +static
> +struct s3c24xx_dma_phy *s3c24xx_dma_get_phy(struct s3c24xx_dma_chan
> *s3cchan) +{
> +	struct s3c24xx_dma_engine *s3cdma = s3cchan->host;
> +	const struct s3c24xx_dma_platdata *pdata = s3cdma->pdata;
> +	struct s3c24xx_dma_channel *cdata;
> +	struct s3c24xx_dma_phy *phy = NULL;
> +	unsigned long flags;
> +	int i;
> +	int ret;
> +
> +	if (s3cchan->slave)
> +		cdata = &pdata->channels[s3cchan->id];
> +
> +	for (i = 0; i < s3cdma->pdata->num_phy_channels; i++) {
> +		phy = &s3cdma->phy_chans[i];
> +
> +		if (!phy || !phy->valid)

Hmm, is it even possible here for phy to be NULL? This would happen only 
at i == 0 and s3cdma->phy_chans == NULL.

> +			continue;
> +
> +		if (!s3c24xx_dma_phy_valid(s3cchan, phy))
> +			continue;
> +
> +		spin_lock_irqsave(&phy->lock, flags);
> +
> +		if (!phy->serving) {
> +			phy->serving = s3cchan;
> +			spin_unlock_irqrestore(&phy->lock, flags);
> +			break;
> +		}
> +
> +		spin_unlock_irqrestore(&phy->lock, flags);
> +	}
> +
> +	/* No physical channel available, cope with it */
> +	if (i == s3cdma->pdata->num_phy_channels) {
> +		dev_warn(&s3cdma->pdev->dev, "no phy channel 
available\n");
> +		return NULL;
> +	}
> +
> +	/* start the phy clock */
> +	if (s3cdma->sdata->has_clocks) {
> +		ret = clk_enable(phy->clk);
> +		if (ret) {

nit: Some error message could be printed here.

> +			phy->serving = NULL;
> +			return NULL;
> +		}
> +	}
> +
> +	return phy;
> +}
> +
> +/*
> + * Mark the physical channel as free.
> + *
> + * This drops the link between the physical and virtual channel.
> + */
> +static inline void s3c24xx_dma_put_phy(struct s3c24xx_dma_phy *phy)
> +{
> +	struct s3c24xx_dma_engine *s3cdma = phy->host;
> +
> +	if (s3cdma->sdata->has_clocks)
> +		clk_disable(phy->clk);
> +
> +	phy->serving = NULL;
> +}
> +
> +/*
> + * Stops the channel by writing the stop bit.
> + * This should not be used for an on-going transfer, but as a method of
> + * shutting down a channel (eg, when it's no longer used) or
> terminating a + * transfer.
> + */
> +static void s3c24xx_dma_terminate_phy(struct s3c24xx_dma_phy *phy)
> +{
> +	writel(S3C24XX_DMASKTRIG_STOP, phy->base + S3C24XX_DMASKTRIG);
> +}
> +
> +/*
> + * Virtual channel handling
> + */
> +
> +static inline
> +struct s3c24xx_dma_chan *to_s3c24xx_dma_chan(struct dma_chan *chan)
> +{
> +	return container_of(chan, struct s3c24xx_dma_chan, vc.chan);
> +}
> +
> +static u32 s3c24xx_dma_getbytes_chan(struct s3c24xx_dma_chan *s3cchan)
> +{
> +	struct s3c24xx_dma_phy *phy = s3cchan->phy;
> +	struct s3c24xx_txd *txd = s3cchan->at;
> +	u32 tc = readl(phy->base + S3C24XX_DSTAT) & 
S3C24XX_DSTAT_CURRTC_MASK;
> +
> +	return tc * txd->width;
> +}
> +
> +static int s3c24xx_dma_set_runtime_config(struct s3c24xx_dma_chan
> *s3cchan, +				  struct dma_slave_config *config)
> +{
> +	if (!s3cchan->slave)
> +		return -EINVAL;
> +
> +	/* Reject definitely invalid configurations */
> +	if (config->src_addr_width == DMA_SLAVE_BUSWIDTH_8_BYTES ||
> +	    config->dst_addr_width == DMA_SLAVE_BUSWIDTH_8_BYTES)
> +		return -EINVAL;
> +
> +	s3cchan->cfg = *config;
> +
> +	return 0;
> +}
> +
> +/*
> + * Transfer handling
> + */
> +
> +static inline
> +struct s3c24xx_txd *to_s3c24xx_txd(struct dma_async_tx_descriptor *tx)
> +{
> +	return container_of(tx, struct s3c24xx_txd, vd.tx);
> +}
> +
> +static struct s3c24xx_txd *s3c24xx_dma_get_txd(void)
> +{
> +	struct s3c24xx_txd *txd = kzalloc(sizeof(*txd), GFP_NOWAIT);
> +
> +	if (txd) {
> +		INIT_LIST_HEAD(&txd->dsg_list);
> +		txd->dcon = S3C24XX_DCON_INT | S3C24XX_DCON_NORELOAD;
> +	}
> +
> +	return txd;
> +}
> +
> +static void s3c24xx_dma_free_txd(struct s3c24xx_txd *txd)
> +{
> +	struct s3c24xx_sg *dsg, *_dsg;
> +
> +	list_for_each_entry_safe(dsg, _dsg, &txd->dsg_list, node) {
> +		list_del(&dsg->node);
> +		kfree(dsg);
> +	}
> +
> +	kfree(txd);
> +}
> +
> +static void s3c24xx_dma_start_next_sg(struct s3c24xx_dma_chan *s3cchan,
> +				       struct s3c24xx_txd *txd)
> +{
> +	struct s3c24xx_dma_engine *s3cdma = s3cchan->host;
> +	struct s3c24xx_dma_phy *phy = s3cchan->phy;
> +	const struct s3c24xx_dma_platdata *pdata = s3cdma->pdata;
> +	struct s3c24xx_sg *dsg = list_entry(txd->at, struct s3c24xx_sg, 
node);
> +	u32 dcon = txd->dcon;
> +	u32 val;
> +
> +	/* transfer-size and -count from len and width */
> +	switch (txd->width) {
> +	case 1:
> +		dcon |= S3C24XX_DCON_DSZ_BYTE | dsg->len;
> +		break;
> +	case 2:
> +		dcon |= S3C24XX_DCON_DSZ_HALFWORD | (dsg->len / 2);
> +		break;
> +	case 4:
> +		dcon |= S3C24XX_DCON_DSZ_WORD | (dsg->len / 4);
> +		break;
> +	}
> +
> +	if (s3cchan->slave) {
> +		struct s3c24xx_dma_channel *cdata =
> +					&pdata->channels[s3cchan->id];

Coding style: A blank line should be present between variable declarations 
and code.

> +		if (s3cdma->sdata->has_reqsel) {
> +			writel_relaxed((cdata->chansel << 1) |
> +							
S3C24XX_DMAREQSEL_HW,
> +					phy->base + S3C24XX_DMAREQSEL);
> +		} else {
> +			int csel = cdata->chansel >> (phy->id *
> +							
S3C24XX_CHANSEL_WIDTH);

Ditto.

> +			csel &= S3C24XX_CHANSEL_REQ_MASK;
> +			dcon |= csel << S3C24XX_DCON_HWSRC_SHIFT;
> +			dcon |= S3C24XX_DCON_HWTRIG;
> +		}
> +	} else {
> +		if (s3cdma->sdata->has_reqsel)
> +			writel_relaxed(0, phy->base + S3C24XX_DMAREQSEL);
> +	}
> +
> +	writel_relaxed(dsg->src_addr, phy->base + S3C24XX_DISRC);
> +	writel_relaxed(txd->disrcc, phy->base + S3C24XX_DISRCC);
> +	writel_relaxed(dsg->dst_addr, phy->base + S3C24XX_DIDST);
> +	writel_relaxed(txd->didstc, phy->base + S3C24XX_DIDSTC);
> +	writel_relaxed(dcon, phy->base + S3C24XX_DCON);
> +
> +	val = readl_relaxed(phy->base + S3C24XX_DMASKTRIG);
> +	val &= ~S3C24XX_DMASKTRIG_STOP;
> +	val |= S3C24XX_DMASKTRIG_ON;
> +
> +	/* trigger the dma operation for memcpy transfers */
> +	if (!s3cchan->slave)
> +		val |= S3C24XX_DMASKTRIG_SWTRIG;
> +
> +	writel(val, phy->base + S3C24XX_DMASKTRIG);
> +}
> +
> +/*
> + * Set the initial DMA register values and start first sg.
> + */
> +static void s3c24xx_dma_start_next_txd(struct s3c24xx_dma_chan
> *s3cchan) +{
> +	struct s3c24xx_dma_phy *phy = s3cchan->phy;
> +	struct virt_dma_desc *vd = vchan_next_desc(&s3cchan->vc);
> +	struct s3c24xx_txd *txd = to_s3c24xx_txd(&vd->tx);
> +
> +	list_del(&txd->vd.node);
> +
> +	s3cchan->at = txd;
> +
> +	/* Wait for channel inactive */
> +	while (s3c24xx_dma_phy_busy(phy))
> +		cpu_relax();
> +
> +	/* point to the first element of the sg list */
> +	txd->at = txd->dsg_list.next;
> +	s3c24xx_dma_start_next_sg(s3cchan, txd);
> +}
> +
> +static void s3c24xx_dma_free_txd_list(struct s3c24xx_dma_engine
> *s3cdma, +				struct s3c24xx_dma_chan *s3cchan)
> +{
> +	LIST_HEAD(head);
> +
> +	vchan_get_all_descriptors(&s3cchan->vc, &head);
> +	vchan_dma_desc_free_list(&s3cchan->vc, &head);
> +}
> +
> +/*
> + * Try to allocate a physical channel.  When successful, assign it to
> + * this virtual channel, and initiate the next descriptor.  The
> + * virtual channel lock must be held at this point.
> + */
> +static void s3c24xx_dma_phy_alloc_and_start(struct s3c24xx_dma_chan
> *s3cchan) +{
> +	struct s3c24xx_dma_engine *s3cdma = s3cchan->host;
> +	struct s3c24xx_dma_phy *phy;
> +
> +	phy = s3c24xx_dma_get_phy(s3cchan);
> +	if (!phy) {
> +		dev_dbg(&s3cdma->pdev->dev, "no physical channel available 
for xfer
> on %s\n", +			s3cchan->name);
> +		s3cchan->state = S3C24XX_DMA_CHAN_WAITING;
> +		return;
> +	}
> +
> +	dev_dbg(&s3cdma->pdev->dev, "allocated physical channel %d for 
xfer on
> %s\n", +		phy->id, s3cchan->name);
> +
> +	s3cchan->phy = phy;
> +	s3cchan->state = S3C24XX_DMA_CHAN_RUNNING;
> +
> +	s3c24xx_dma_start_next_txd(s3cchan);
> +}
> +
> +static void s3c24xx_dma_phy_reassign_start(struct s3c24xx_dma_phy *phy,
> +	struct s3c24xx_dma_chan *s3cchan)
> +{
> +	struct s3c24xx_dma_engine *s3cdma = s3cchan->host;
> +
> +	dev_dbg(&s3cdma->pdev->dev, "reassigned physical channel %d for 
xfer
> on %s\n", +		phy->id, s3cchan->name);
> +
> +	/*
> +	 * We do this without taking the lock; we're really only concerned
> +	 * about whether this pointer is NULL or not, and we're guaranteed
> +	 * that this will only be called when it _already_ is non-NULL.
> +	 */
> +	phy->serving = s3cchan;
> +	s3cchan->phy = phy;
> +	s3cchan->state = S3C24XX_DMA_CHAN_RUNNING;
> +	s3c24xx_dma_start_next_txd(s3cchan);
> +}
> +
> +/*
> + * Free a physical DMA channel, potentially reallocating it to another
> + * virtual channel if we have any pending.
> + */
> +static void s3c24xx_dma_phy_free(struct s3c24xx_dma_chan *s3cchan)
> +{
> +	struct s3c24xx_dma_engine *s3cdma = s3cchan->host;
> +	struct s3c24xx_dma_chan *p, *next;
> +
> +retry:
> +	next = NULL;
> +
> +	/* Find a waiting virtual channel for the next transfer. */
> +	list_for_each_entry(p, &s3cdma->memcpy.channels, 
vc.chan.device_node)
> +		if (p->state == S3C24XX_DMA_CHAN_WAITING) {
> +			next = p;
> +			break;
> +		}
> +
> +	if (!next) {
> +		list_for_each_entry(p, &s3cdma->slave.channels,
> +				    vc.chan.device_node)
> +			if (p->state == S3C24XX_DMA_CHAN_WAITING &&
> +				      s3c24xx_dma_phy_valid(p, s3cchan-
>phy)) {
> +				next = p;
> +				break;
> +			}
> +	}
> +
> +	/* Ensure that the physical channel is stopped */
> +	s3c24xx_dma_terminate_phy(s3cchan->phy);
> +
> +	if (next) {
> +		bool success;
> +
> +		/*
> +		 * Eww.  We know this isn't going to deadlock
> +		 * but lockdep probably doesn't.
> +		 */
> +		spin_lock(&next->vc.lock);
> +		/* Re-check the state now that we have the lock */
> +		success = next->state == S3C24XX_DMA_CHAN_WAITING;
> +		if (success)
> +			s3c24xx_dma_phy_reassign_start(s3cchan->phy, 
next);
> +		spin_unlock(&next->vc.lock);
> +
> +		/* If the state changed, try to find another channel */
> +		if (!success)
> +			goto retry;
> +	} else {
> +		/* No more jobs, so free up the physical channel */
> +		s3c24xx_dma_put_phy(s3cchan->phy);
> +	}
> +
> +	s3cchan->phy = NULL;
> +	s3cchan->state = S3C24XX_DMA_CHAN_IDLE;
> +}
> +
> +static void s3c24xx_dma_unmap_buffers(struct s3c24xx_txd *txd)
> +{
> +	struct device *dev = txd->vd.tx.chan->device->dev;
> +	struct s3c24xx_sg *dsg;
> +
> +	if (!(txd->vd.tx.flags & DMA_COMPL_SKIP_SRC_UNMAP)) {
> +		if (txd->vd.tx.flags & DMA_COMPL_SRC_UNMAP_SINGLE)
> +			list_for_each_entry(dsg, &txd->dsg_list, node)
> +				dma_unmap_single(dev, dsg->src_addr, dsg-
>len,
> +						DMA_TO_DEVICE);
> +		else {
> +			list_for_each_entry(dsg, &txd->dsg_list, node)
> +				dma_unmap_page(dev, dsg->src_addr, dsg-
>len,
> +						DMA_TO_DEVICE);
> +		}
> +	}
> +
> +	if (!(txd->vd.tx.flags & DMA_COMPL_SKIP_DEST_UNMAP)) {
> +		if (txd->vd.tx.flags & DMA_COMPL_DEST_UNMAP_SINGLE)
> +			list_for_each_entry(dsg, &txd->dsg_list, node)
> +				dma_unmap_single(dev, dsg->dst_addr, dsg-
>len,
> +						DMA_FROM_DEVICE);
> +		else
> +			list_for_each_entry(dsg, &txd->dsg_list, node)
> +				dma_unmap_page(dev, dsg->dst_addr, dsg-
>len,
> +						DMA_FROM_DEVICE);
> +	}
> +}
> +
> +static void s3c24xx_dma_desc_free(struct virt_dma_desc *vd)
> +{
> +	struct s3c24xx_txd *txd = to_s3c24xx_txd(&vd->tx);
> +	struct s3c24xx_dma_chan *s3cchan = to_s3c24xx_dma_chan(vd-
>tx.chan);
> +
> +	if (!s3cchan->slave)
> +		s3c24xx_dma_unmap_buffers(txd);
> +
> +	s3c24xx_dma_free_txd(txd);
> +}
> +
> +static irqreturn_t s3c24xx_dma_irq(int irq, void *data)
> +{
> +	struct s3c24xx_dma_phy *phy = data;
> +	struct s3c24xx_dma_chan *s3cchan = phy->serving;
> +	struct s3c24xx_txd *txd;
> +
> +	dev_dbg(&phy->host->pdev->dev, "interrupt on channel %d\n", phy-
>id);
> +
> +	/*
> +	 * Interrupts happen to notify the completion of a transfer and 
the
> +	 * channel should have moved into its stop state already on its 
own.
> +	 * Therefore interrupts on channels not bound to a virtual channel
> +	 * should never happen. Nevertheless send a terminate command to 
the
> +	 * channel if the unlikely case happens.
> +	 */
> +	if (unlikely(!s3cchan)) {
> +		dev_err(&phy->host->pdev->dev, "interrupt on unused 
channel %d\n",
> +			phy->id);
> +
> +		s3c24xx_dma_terminate_phy(phy);
> +
> +		return IRQ_HANDLED;
> +	}
> +
> +	spin_lock(&s3cchan->vc.lock);
> +	txd = s3cchan->at;
> +	if (txd) {
> +		/* when more sg's are in this txd, start the next one */
> +		if (!list_is_last(txd->at, &txd->dsg_list)) {
> +			txd->at = txd->at->next;
> +			s3c24xx_dma_start_next_sg(s3cchan, txd);
> +		} else {
> +			s3cchan->at = NULL;
> +			vchan_cookie_complete(&txd->vd);
> +
> +			/*
> +			 * And start the next descriptor (if any),
> +			 * otherwise free this channel.
> +			 */
> +			if (vchan_next_desc(&s3cchan->vc))
> +				s3c24xx_dma_start_next_txd(s3cchan);
> +			else
> +				s3c24xx_dma_phy_free(s3cchan);
> +		}
> +	}
> +	spin_unlock(&s3cchan->vc.lock);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +/*
> + * The DMA ENGINE API
> + */
> +
> +static int s3c24xx_dma_control(struct dma_chan *chan, enum dma_ctrl_cmd
> cmd, +			 unsigned long arg)
> +{
> +	struct s3c24xx_dma_chan *s3cchan = to_s3c24xx_dma_chan(chan);
> +	struct s3c24xx_dma_engine *s3cdma = s3cchan->host;
> +	unsigned long flags;
> +	int ret = 0;
> +
> +	/* Controls applicable to inactive channels */
> +	if (cmd == DMA_SLAVE_CONFIG)
> +		return s3c24xx_dma_set_runtime_config(s3cchan,
> +					      (struct dma_slave_config 
*)arg);
> +
> +	/*
> +	 * Anything succeeds on channels with no physical allocation and
> +	 * no queued transfers.
> +	 */
> +	spin_lock_irqsave(&s3cchan->vc.lock, flags);
> +	if (!s3cchan->phy && !s3cchan->at) {
> +		spin_unlock_irqrestore(&s3cchan->vc.lock, flags);
> +		return 0;
> +	}
> +
> +	switch (cmd) {
> +	case DMA_TERMINATE_ALL:
> +		s3cchan->state = S3C24XX_DMA_CHAN_IDLE;
> +
> +		 /* Mark physical channel as free */
> +		if (s3cchan->phy)
> +			s3c24xx_dma_phy_free(s3cchan);
> +
> +		/* Dequeue current job */
> +		if (s3cchan->at) {
> +			s3c24xx_dma_desc_free(&s3cchan->at->vd);
> +			s3cchan->at = NULL;
> +		}
> +
> +		/* Dequeue jobs not yet fired as well */
> +		s3c24xx_dma_free_txd_list(s3cdma, s3cchan);
> +		break;
> +	default:
> +		/* Unknown command */
> +		ret = -ENXIO;
> +		break;
> +	}
> +
> +	spin_unlock_irqrestore(&s3cchan->vc.lock, flags);
> +
> +	return ret;
> +}
> +
> +static int s3c24xx_dma_alloc_chan_resources(struct dma_chan *chan)
> +{
> +	return 0;
> +}
> +
> +static void s3c24xx_dma_free_chan_resources(struct dma_chan *chan)
> +{
> +	/* Ensure all queued descriptors are freed */
> +	vchan_free_chan_resources(to_virt_chan(chan));
> +}
> +
> +static enum dma_status s3c24xx_dma_tx_status(struct dma_chan *chan,
> +		dma_cookie_t cookie, struct dma_tx_state *txstate)
> +{
> +	struct s3c24xx_dma_chan *s3cchan = to_s3c24xx_dma_chan(chan);
> +	struct virt_dma_desc *vd;
> +	unsigned long flags;
> +	enum dma_status ret;
> +	size_t bytes = 0;
> +
> +	ret = dma_cookie_status(chan, cookie, txstate);
> +	if (ret == DMA_SUCCESS)
> +		return ret;
> +
> +	/*
> +	 * There's no point calculating the residue if there's
> +	 * no txstate to store the value.
> +	 */
> +	if (!txstate)
> +		return ret;
> +
> +	spin_lock_irqsave(&s3cchan->vc.lock, flags);
> +	ret = dma_cookie_status(chan, cookie, txstate);
> +	if (ret != DMA_SUCCESS) {
> +		struct s3c24xx_txd *txd;
> +		struct s3c24xx_sg *dsg;
> +
> +		vd = vchan_find_desc(&s3cchan->vc, cookie);
> +		if (vd) {
> +			/* On the issued list, so hasn't been processed 
yet */
> +			txd = to_s3c24xx_txd(&vd->tx);
> +
> +			list_for_each_entry(dsg, &txd->dsg_list, node)
> +				bytes += dsg->len;
> +		} else {
> +			/*
> +			 * Currently running, so sum over the pending sg's 
and
> +			 * the currently active one.
> +			 */
> +			txd = s3cchan->at;
> +
> +			dsg = list_entry(txd->at, struct s3c24xx_sg, 
node);
> +			list_for_each_entry_from(dsg, &txd->dsg_list, 
node);
> +				bytes += dsg->len;
> +
> +			bytes += s3c24xx_dma_getbytes_chan(s3cchan);
> +		}
> +	}
> +	spin_unlock_irqrestore(&s3cchan->vc.lock, flags);
> +
> +	/*
> +	 * This cookie not complete yet
> +	 * Get number of bytes left in the active transactions and queue
> +	 */
> +	dma_set_residue(txstate, bytes);
> +
> +	/* Whether waiting or running, we're in progress */
> +	return ret;
> +}
> +
> +/*
> + * Initialize a descriptor to be used by memcpy submit
> + */
> +static struct dma_async_tx_descriptor *s3c24xx_dma_prep_memcpy(
> +		struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
> +		size_t len, unsigned long flags)
> +{
> +	struct s3c24xx_dma_chan *s3cchan = to_s3c24xx_dma_chan(chan);
> +	struct s3c24xx_dma_engine *s3cdma = s3cchan->host;
> +	struct s3c24xx_txd *txd;
> +	struct s3c24xx_sg *dsg;
> +
> +	dev_dbg(&s3cdma->pdev->dev, "prepare memcpy of %d bytes from 
%s\n",
> +			len, s3cchan->name);
> +
> +	if ((len & S3C24XX_DCON_TC_MASK) != len) {
> +		dev_err(&s3cdma->pdev->dev, "memcpy size %d to large\n", 
len);
> +		return NULL;
> +	}
> +
> +	txd = s3c24xx_dma_get_txd();
> +	if (!txd)
> +		return NULL;
> +
> +	dsg = kzalloc(sizeof(struct s3c24xx_sg), GFP_NOWAIT);
> +	if (!dsg) {
> +		s3c24xx_dma_free_txd(txd);
> +		return NULL;
> +	}
> +	list_add_tail(&dsg->node, &txd->dsg_list);
> +
> +	dsg->src_addr = src;
> +	dsg->dst_addr = dest;
> +	dsg->len = len;
> +
> +	txd->width = 1;

Hmm, should memcpy transfers be really 1-byte wide? Not that it would be 
used by anything anyway, as the only users of DMA on Samsung platforms 
currently are SPI and ASoC...

> +	txd->disrcc = S3C24XX_DISRCC_LOC_AHB | 
S3C24XX_DISRCC_INC_INCREMENT;
> +	txd->didstc = S3C24XX_DIDSTC_LOC_AHB | 
S3C24XX_DIDSTC_INC_INCREMENT;
> +	txd->dcon |= S3C24XX_DCON_DEMAND | S3C24XX_DCON_SYNC_HCLK |
> +		     S3C24XX_DCON_SERV_WHOLE;
> +
> +	return vchan_tx_prep(&s3cchan->vc, &txd->vd, flags);
> +}
> +
> +static struct dma_async_tx_descriptor *s3c24xx_dma_prep_slave_sg(
> +		struct dma_chan *chan, struct scatterlist *sgl,
> +		unsigned int sg_len, enum dma_transfer_direction 
direction,
> +		unsigned long flags, void *context)
> +{
> +	struct s3c24xx_dma_chan *s3cchan = to_s3c24xx_dma_chan(chan);
> +	struct s3c24xx_dma_engine *s3cdma = s3cchan->host;
> +	const struct s3c24xx_dma_platdata *pdata = s3cdma->pdata;
> +	struct s3c24xx_dma_channel *cdata = &pdata->channels[s3cchan->id];
> +	struct s3c24xx_txd *txd;
> +	struct s3c24xx_sg *dsg;
> +	struct scatterlist *sg;
> +	dma_addr_t slave_addr;
> +	u32 hwcfg = 0;
> +	int tmp;
> +
> +	dev_dbg(&s3cdma->pdev->dev, "prepare transaction of %d bytes from
> %s\n", +			sg_dma_len(sgl), s3cchan->name);
> +
> +	txd = s3c24xx_dma_get_txd();
> +	if (!txd)
> +		return NULL;
> +
> +	if (cdata->handshake)
> +		txd->dcon |= S3C24XX_DCON_HANDSHAKE;
> +
> +	switch (cdata->bus) {
> +	case S3C24XX_DMA_APB:
> +		txd->dcon |= S3C24XX_DCON_SYNC_PCLK;
> +		hwcfg |= S3C24XX_DISRCC_LOC_APB;
> +		break;
> +	case S3C24XX_DMA_AHB:
> +		txd->dcon |= S3C24XX_DCON_SYNC_HCLK;
> +		hwcfg |= S3C24XX_DISRCC_LOC_AHB;
> +		break;
> +	}
> +
> +	/* always assume our peripheral desintation is a fixed
> +	 * address in memory. */

coding style: Multiline comments should start and end with one empty line.

> +	hwcfg |= S3C24XX_DISRCC_INC_FIXED;
> +
> +	/* individual dma operations are requested by the slave,
> +	 * so serve only single atomic operations 
(S3C24XX_DCON_SERV_SINGLE).
> +	 */

Ditto.

> +	txd->dcon |= S3C24XX_DCON_SERV_SINGLE;
> +
> +	if (direction == DMA_MEM_TO_DEV) {
> +		txd->disrcc = S3C24XX_DISRCC_LOC_AHB |
> +			      S3C24XX_DISRCC_INC_INCREMENT;
> +		txd->didstc = hwcfg;
> +		slave_addr = s3cchan->cfg.dst_addr;
> +		txd->width = s3cchan->cfg.dst_addr_width;
> +	} else if (direction == DMA_DEV_TO_MEM) {
> +		txd->disrcc = hwcfg;
> +		txd->didstc = S3C24XX_DIDSTC_LOC_AHB |
> +			      S3C24XX_DIDSTC_INC_INCREMENT;
> +		slave_addr = s3cchan->cfg.src_addr;
> +		txd->width = s3cchan->cfg.src_addr_width;
> +	} else {
> +		s3c24xx_dma_free_txd(txd);
> +		dev_err(&s3cdma->pdev->dev,
> +			"direction %d unsupported\n", direction);
> +		return NULL;
> +	}
> +
> +	for_each_sg(sgl, sg, sg_len, tmp) {
> +		dsg = kzalloc(sizeof(struct s3c24xx_sg), GFP_NOWAIT);
> +		if (!dsg) {
> +			s3c24xx_dma_free_txd(txd);
> +			return NULL;
> +		}
> +		list_add_tail(&dsg->node, &txd->dsg_list);
> +
> +		dsg->len = sg_dma_len(sg);
> +		if (direction == DMA_MEM_TO_DEV) {
> +			dsg->src_addr = sg_dma_address(sg);
> +			dsg->dst_addr = slave_addr;
> +		} else { /* DMA_DEV_TO_MEM */
> +			dsg->src_addr = slave_addr;
> +			dsg->dst_addr = sg_dma_address(sg);
> +		}
> +		break;
> +	}
> +
> +	return vchan_tx_prep(&s3cchan->vc, &txd->vd, flags);
> +}
> +
> +/*
> + * Slave transactions callback to the slave device to allow
> + * synchronization of slave DMA signals with the DMAC enable
> + */
> +static void s3c24xx_dma_issue_pending(struct dma_chan *chan)
> +{
> +	struct s3c24xx_dma_chan *s3cchan = to_s3c24xx_dma_chan(chan);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&s3cchan->vc.lock, flags);
> +	if (vchan_issue_pending(&s3cchan->vc)) {
> +		if (!s3cchan->phy && s3cchan->state != 
S3C24XX_DMA_CHAN_WAITING)
> +			s3c24xx_dma_phy_alloc_and_start(s3cchan);
> +	}
> +	spin_unlock_irqrestore(&s3cchan->vc.lock, flags);
> +}
> +
> +/*
> + * Bringup and teardown
> + */
> +
> +/*
> + * Initialise the DMAC memcpy/slave channels.
> + * Make a local wrapper to hold required data
> + */
> +static int s3c24xx_dma_init_virtual_channels(struct s3c24xx_dma_engine
> *s3cdma, +		struct dma_device *dmadev, unsigned int channels, 
bool
> slave) +{
> +	struct s3c24xx_dma_chan *chan;
> +	int i;
> +
> +	INIT_LIST_HEAD(&dmadev->channels);
> +
> +	/*
> +	 * Register as many many memcpy as we have physical channels,
> +	 * we won't always be able to use all but the code will have
> +	 * to cope with that situation.
> +	 */
> +	for (i = 0; i < channels; i++) {
> +		chan = devm_kzalloc(dmadev->dev, sizeof(*chan), 
GFP_KERNEL);
> +		if (!chan) {
> +			dev_err(dmadev->dev,
> +				"%s no memory for channel\n", __func__);
> +			return -ENOMEM;
> +		}
> +
> +		chan->id = i;
> +		chan->host = s3cdma;
> +		chan->state = S3C24XX_DMA_CHAN_IDLE;
> +
> +		if (slave) {
> +			chan->slave = true;
> +			chan->name = kasprintf(GFP_KERNEL, "slave%d", i);
> +			if (!chan->name)
> +				return -ENOMEM;
> +		} else {
> +			chan->name = kasprintf(GFP_KERNEL, "memcpy%d", i);
> +			if (!chan->name)
> +				return -ENOMEM;
> +		}
> +		dev_dbg(dmadev->dev,
> +			 "initialize virtual channel \"%s\"\n",
> +			 chan->name);
> +
> +		chan->vc.desc_free = s3c24xx_dma_desc_free;
> +		vchan_init(&chan->vc, dmadev);
> +	}
> +	dev_info(dmadev->dev, "initialized %d virtual %s channels\n",
> +		 i, slave ? "slave" : "memcpy");
> +	return i;
> +}
> +
> +static void s3c24xx_dma_free_virtual_channels(struct dma_device
> *dmadev) +{
> +	struct s3c24xx_dma_chan *chan = NULL;
> +	struct s3c24xx_dma_chan *next;
> +
> +	list_for_each_entry_safe(chan,
> +				 next, &dmadev->channels, 
vc.chan.device_node)
> +		list_del(&chan->vc.chan.device_node);
> +}
> +
> +/* s3c2412 and s3c2413 have a 0x40 stride and dmareqsel mechanism */
> +static struct soc_data soc_s3c2412 = {
> +	.stride = 0x40,
> +	.has_reqsel = true,
> +	.has_clocks = true,
> +};
> +
> +/* s3c2443 and following have a 0x100 stride and dmareqsel mechanism */
> +static struct soc_data soc_s3c2443 = {
> +	.stride = 0x100,
> +	.has_reqsel = true,
> +	.has_clocks = true,
> +};
> +
> +static struct platform_device_id s3c24xx_dma_driver_ids[] = {
> +	{
> +		.name		= "s3c2412-dma",
> +		.driver_data	= (kernel_ulong_t)&soc_s3c2412,
> +	}, {
> +		.name		= "s3c2443-dma",
> +		.driver_data	= (kernel_ulong_t)&soc_s3c2443,
> +	},
> +	{ },
> +};
> +
> +static struct soc_data *s3c24xx_dma_get_soc_data(struct platform_device
> *pdev) +{
> +	return (struct soc_data *)
> +			 platform_get_device_id(pdev)->driver_data;
> +}
> +
> +static int s3c24xx_dma_probe(struct platform_device *pdev)
> +{
> +	const struct s3c24xx_dma_platdata *pdata =
> dev_get_platdata(&pdev->dev); +	struct soc_data *sdata;
> +	struct s3c24xx_dma_engine *s3cdma;
> +	struct resource *res;
> +	int ret;
> +	int i;
> +
> +	if (!pdata) {
> +		dev_err(&pdev->dev, "platform data missing\n");
> +		return -ENODEV;
> +	}
> +
> +	/* Basic sanity check */
> +	if (pdata->num_phy_channels > MAX_DMA_CHANNELS) {
> +		dev_err(&pdev->dev, "to many dma channels %d, max %d\n",
> +			pdata->num_phy_channels, MAX_DMA_CHANNELS);
> +		return -EINVAL;
> +	}
> +
> +	sdata = s3c24xx_dma_get_soc_data(pdev);
> +	if (!sdata)
> +		return -EINVAL;
> +
> +	s3cdma = devm_kzalloc(&pdev->dev, sizeof(*s3cdma), GFP_KERNEL);
> +	if (!s3cdma)
> +		return -ENOMEM;
> +
> +	s3cdma->pdev = pdev;
> +	s3cdma->pdata = pdata;
> +	s3cdma->sdata = sdata;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	s3cdma->base = devm_request_and_ioremap(&pdev->dev, res);

nit: devm_request_and_ioremap() is deprecated and devm_ioremap_resource() 
should be used instead (remembering that it returns ERR_PTR() not NULL on 
errors).

> +	if (!s3cdma->base) {
> +		dev_err(&pdev->dev, "could not map dma registers\n");
> +		return -EBUSY;
> +	}
> +
> +	s3cdma->phy_chans = devm_kzalloc(&pdev->dev,
> +					      sizeof(struct 
s3c24xx_dma_phy) *
> +							pdata-
>num_phy_channels,
> +					      GFP_KERNEL);
> +	if (!s3cdma->phy_chans)
> +		return -ENOMEM;
> +
> +	/* aquire irqs and clocks for all physical channels */
> +	for (i = 0; i < pdata->num_phy_channels; i++) {
> +		struct s3c24xx_dma_phy *phy = &s3cdma->phy_chans[i];
> +		char clk_name[6];
> +
> +		phy->id = i;
> +		phy->base = s3cdma->base + (i * sdata->stride);
> +		phy->host = s3cdma;
> +
> +		sprintf(clk_name, "dma.%d", i);
> +		phy->clk = devm_clk_get(&pdev->dev, clk_name);
> +		if (IS_ERR(phy->clk) && sdata->has_clocks) {
> +			dev_err(&pdev->dev, "unable to aquire clock for 
channel %d, error
> %lu", +				i, PTR_ERR(phy->clk));
> +			continue;
> +		}

Shouldn't the above clock getting code be simply moved under the if clause 
below?

> +
> +		if (sdata->has_clocks) {
> +			ret = clk_prepare(phy->clk);
> +			if (ret) {
> +				dev_err(&pdev->dev, "clock for phy %d 
failed, error %d\n",
> +					i, ret);
> +				continue;
> +			}
> +		}
> +
> +		res = platform_get_resource(pdev, IORESOURCE_IRQ, i);
> +		if (res)
> +			phy->irq = res->start;

nit: platform_get_irq() could be used here.

> +		if (!phy->irq) {
> +			dev_err(&pdev->dev, "failed to get irq %d\n", i);
> +			continue;
> +		}
> +
> +		ret = devm_request_irq(&pdev->dev, phy->irq, 
s3c24xx_dma_irq,
> +				       0, pdev->name, phy);
> +		if (ret) {
> +			dev_err(&pdev->dev, "Unable to request irq for 
channel %d, error
> %d\n", +				i, ret);
> +			continue;
> +		}
> +
> +		spin_lock_init(&phy->lock);
> +		phy->valid = true;
> +
> +		dev_dbg(&pdev->dev, "physical channel %d is %s\n",
> +			i, s3c24xx_dma_phy_busy(phy) ? "BUSY" : "FREE");
> +	}
> +
> +	/* Initialize memcpy engine */
> +	dma_cap_set(DMA_MEMCPY, s3cdma->memcpy.cap_mask);
> +	dma_cap_set(DMA_PRIVATE, s3cdma->memcpy.cap_mask);
> +	s3cdma->memcpy.dev = &pdev->dev;
> +	s3cdma->memcpy.device_alloc_chan_resources =
> +					s3c24xx_dma_alloc_chan_resources;
> +	s3cdma->memcpy.device_free_chan_resources =
> +					s3c24xx_dma_free_chan_resources;
> +	s3cdma->memcpy.device_prep_dma_memcpy = s3c24xx_dma_prep_memcpy;
> +	s3cdma->memcpy.device_tx_status = s3c24xx_dma_tx_status;
> +	s3cdma->memcpy.device_issue_pending = s3c24xx_dma_issue_pending;
> +	s3cdma->memcpy.device_control = s3c24xx_dma_control;
> +
> +	/* Initialize slave engine for SoC internal dedicated peripherals 
*/
> +	dma_cap_set(DMA_SLAVE, s3cdma->slave.cap_mask);
> +	dma_cap_set(DMA_PRIVATE, s3cdma->slave.cap_mask);
> +	s3cdma->slave.dev = &pdev->dev;
> +	s3cdma->slave.device_alloc_chan_resources =
> +					s3c24xx_dma_alloc_chan_resources;
> +	s3cdma->slave.device_free_chan_resources =
> +					s3c24xx_dma_free_chan_resources;
> +	s3cdma->slave.device_tx_status = s3c24xx_dma_tx_status;
> +	s3cdma->slave.device_issue_pending = s3c24xx_dma_issue_pending;
> +	s3cdma->slave.device_prep_slave_sg = s3c24xx_dma_prep_slave_sg;
> +	s3cdma->slave.device_control = s3c24xx_dma_control;
> +
> +	/* Register as many memcpy channels as there are physical channels 
*/
> +	ret = s3c24xx_dma_init_virtual_channels(s3cdma, &s3cdma->memcpy,
> +						pdata->num_phy_channels, 
false);
> +	if (ret <= 0) {
> +		dev_warn(&pdev->dev,
> +			 "%s failed to enumerate memcpy channels - %d\n",
> +			 __func__, ret);
> +		goto err_memcpy;
> +	}
> +
> +	/* Register slave channels */
> +	ret = s3c24xx_dma_init_virtual_channels(s3cdma, &s3cdma->slave,
> +				pdata->num_channels, true);
> +	if (ret <= 0) {
> +		dev_warn(&pdev->dev,
> +			"%s failed to enumerate slave channels - %d\n",
> +				__func__, ret);
> +		goto err_slave;
> +	}
> +
> +	ret = dma_async_device_register(&s3cdma->memcpy);
> +	if (ret) {
> +		dev_warn(&pdev->dev,
> +			"%s failed to register memcpy as an async device - 
%d\n",
> +			__func__, ret);
> +		goto err_memcpy_reg;
> +	}
> +
> +	ret = dma_async_device_register(&s3cdma->slave);
> +	if (ret) {
> +		dev_warn(&pdev->dev,
> +			"%s failed to register slave as an async device - 
%d\n",
> +			__func__, ret);
> +		goto err_slave_reg;
> +	}
> +
> +	platform_set_drvdata(pdev, s3cdma);
> +	dev_info(&pdev->dev, "Loaded dma driver with %d physical 
channels\n",
> +		 pdata->num_phy_channels);
> +
> +	return 0;
> +
> +err_slave_reg:
> +	dma_async_device_unregister(&s3cdma->memcpy);
> +err_memcpy_reg:
> +	s3c24xx_dma_free_virtual_channels(&s3cdma->slave);
> +err_slave:
> +	s3c24xx_dma_free_virtual_channels(&s3cdma->memcpy);
> +err_memcpy:
> +
> +	return ret;
> +}
> +
> +static struct platform_driver s3c24xx_dma_driver = {
> +	.driver		= {

Hmm, what about .owner field?

> +		.name	= "s3c24xx-dma",
> +	},
> +	.id_table = s3c24xx_dma_driver_ids,
> +};
> +
> +bool s3c24xx_dma_filter(struct dma_chan *chan, void *param)
> +{
> +	struct s3c24xx_dma_chan *s3cchan;
> +
> +	if (chan->device->dev->driver != &s3c24xx_dma_driver.driver)
> +		return false;
> +
> +	s3cchan = to_s3c24xx_dma_chan(chan);
> +
> +	return s3cchan->id == (int)param;
> +}
> +EXPORT_SYMBOL(s3c24xx_dma_filter);
> +
> +static int __init s3c24xx_dma_module_init(void)
> +{
> +	return platform_driver_probe(&s3c24xx_dma_driver, 
s3c24xx_dma_probe);

Hmm, I don't really see any reason to not allow this driver to be compiled 
as a module. IMHO DMA is not necessary for basic system start-up and you 
might want to load DMA driver as a module along with any DMA consumer 
drivers.

Otherwise the driver looks pretty good.

Best regards,
Tomasz

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