Re: [PATCH v3 3/5] mtd: Add support for HyperBus memory devices

[Sergei Shtylyov]

Hello!

On 04/12/2019 12:29 PM, Vignesh Raghavendra wrote:

> Cypress' HyperBus is Low Signal Count, High Performance Double Data Rate
> Bus interface between a host system master and one or more slave
> interfaces. HyperBus is used to connect microprocessor, microcontroller,
> or ASIC devices with random access NOR flash memory (called HyperFlash)
> or self refresh DRAM (called HyperRAM).
> 
> Its a 8-bit data bus (DQ[7:0]) with  Read-Write Data Strobe (RWDS)
> signal and either Single-ended clock(3.0V parts) or Differential clock
> (1.8V parts). It uses ChipSelect lines to select b/w multiple slaves.
> At bus level, it follows a separate protocol described in HyperBus
> specification[1].
> 
> HyperFlash follows CFI AMD/Fujitsu Extended Command Set (0x0002) similar
> to that of existing parallel NORs. Since HyperBus is x8 DDR bus,
> its equivalent to x16 parallel NOR flash wrt bits per clock cycle. But
> HyperBus operates at >166MHz frequencies.
> HyperRAM provides direct random read/write access to flash memory
> array.
> 
> But, HyperBus memory controllers seem to abstract implementation details
> and expose a simple MMIO interface to access connected flash.
> 
> Add support for registering HyperFlash devices with MTD framework. MTD
> maps framework along with CFI chip support framework are used to support
> communicating with flash.
> 
> Framework is modelled along the lines of spi-nor framework. HyperBus
> memory controller (HBMC) drivers calls hyperbus_register_device() to
> register a single HyperFlash device. HyperFlash core parses MMIO access
> information from DT, sets up the map_info struct, probes CFI flash and
> registers it with MTD framework.
> 
> Some HBMC masters need calibration/training sequence[3] to be carried
> out, in order for DLL inside the controller to lock, by reading a known
> string/pattern. This is done by repeatedly reading CFI Query
> Identification String. Calibration needs to be done before trying to detect
> flash as part of CFI flash probe.
> 
> HyperRAM is not supported at the moment.
> 
> HyperBus specification can be found at[1]
> HyperFlash datasheet can be found at[2]
> 
> [1] https://www.cypress.com/file/213356/download
> [2] https://www.cypress.com/file/213346/download
> [3] http://www.ti.com/lit/ug/spruid7b/spruid7b.pdf
>     Table 12-5741. HyperFlash Access Sequence
> 
> Signed-off-by: Vignesh Raghavendra <vigneshr@xxxxxx>
[...]
> diff --git a/drivers/mtd/hyperbus/Kconfig b/drivers/mtd/hyperbus/Kconfig
> new file mode 100644
> index 000000000000..98147e28caa0
> --- /dev/null
> +++ b/drivers/mtd/hyperbus/Kconfig
> @@ -0,0 +1,11 @@
> +menuconfig MTD_HYPERBUS
> +	tristate "HyperBus support"
> +	select MTD_CFI
> +	select MTD_MAP_BANK_WIDTH_2
> +	select MTD_CFI_AMDSTD
> +	select MTD_COMPLEX_MAPPINGS
> +	help
> +	  This is the framework for the HyperBus which can be used by
> +	  the HyperBus Controller driver to communicate with
> +	  HyperFlash. See Cypress HyperBus specification for more
> +	  details
> diff --git a/drivers/mtd/hyperbus/Makefile b/drivers/mtd/hyperbus/Makefile
> new file mode 100644
> index 000000000000..ca61dedd730d
> --- /dev/null
> +++ b/drivers/mtd/hyperbus/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0
> +
> +obj-$(CONFIG_MTD_HYPERBUS)	+= hyperbus-core.o
> diff --git a/drivers/mtd/hyperbus/hyperbus-core.c b/drivers/mtd/hyperbus/hyperbus-core.c
> new file mode 100644
> index 000000000000..49aeb59742c6
> --- /dev/null
> +++ b/drivers/mtd/hyperbus/hyperbus-core.c
> @@ -0,0 +1,192 @@
> +// SPDX-License-Identifier: GPL-2.0
> +//
> +// Copyright (C) 2019 Texas Instruments Incorporated - http://www.ti.com/
> +// Author: Vignesh Raghavendra <vigneshr@xxxxxx>
[...]
> +/* Default calibration routine for use by HyperBus controller.
> + * Controller is calibrated by repeatedly reading known pattern ("QRY"
> + * string from CFI space)
> + * Lets ensure "QRY" string is read correctly at least 5 times to ensure
> + * stability of the DLL lock.
> + */
> +int hyperbus_calibrate(struct hyperbus_device *hbdev)
> +{
> +	struct map_info *map = &hbdev->map;
> +	struct cfi_private cfi;
> +	int count = HYPERBUS_CALIB_COUNT;
> +	int pass_count = 0;
> +	int ret;
> +
> +	cfi.interleave = 1;
> +	cfi.device_type = CFI_DEVICETYPE_X16;
> +	cfi_send_gen_cmd(0xF0, 0, 0, map, &cfi, cfi.device_type, NULL);
> +	cfi_send_gen_cmd(0x98, 0x55, 0, map, &cfi, cfi.device_type, NULL);
> +
> +	while (count--) {
> +		cfi_qry_present(map, 0, &cfi);
> +		ret = cfi_qry_present(map, 0, &cfi);

   Why call it twice in a row?

> +		if (ret)
> +			pass_count++;
> +		else
> +			pass_count = 0;
> +		if (pass_count == 5)
> +			break;
> +	}
> +
> +	cfi_qry_mode_off(0, map, &cfi);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(hyperbus_calibrate);
[...]
> diff --git a/include/linux/mtd/hyperbus.h b/include/linux/mtd/hyperbus.h
> new file mode 100644
> index 000000000000..19340cc56aa4
> --- /dev/null
> +++ b/include/linux/mtd/hyperbus.h
> @@ -0,0 +1,91 @@
[...]
> +/**
> + * hb_unregister_device - deregister HyperBus slave memory device

   You forgot to update the function name in the kernel-doc. :-)

> + * @hbdev: hyperbus_device to be unregistered
> + *
> + * Return: 0 for success, others for failure.
> + */
> +int hyperbus_unregister_device(struct hyperbus_device *hbdev);
> +
> +#endif /* __LINUX_MTD_HYPERBUS_H__ */

MBR, Sergei