Re: [PATCH v4 4/4] tty: serial: 8250: add DFL bus driver for Altera 16550.

[Xu Yilun]

On 2022-10-20 at 14:26:10 -0700, matthew.gerlach@xxxxxxxxxxxxxxx wrote:
> From: Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx>
> 
> Add a Device Feature List (DFL) bus driver for the Altera
> 16550 implementation of UART.
> 
> Signed-off-by: Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx>
> ---
> v4: use dev_err_probe() everywhere that is appropriate
>     clean up noise
>     change error messages to use the word, unsupported
>     tried again to sort Makefile and KConfig better
>     reorder probe function for easier error handling
>     use new dfh_find_param API
> 
> v3: use passed in location of registers
>     use cleaned up functions for parsing parameters
> 
> v2: clean up error messages
>     alphabetize header files
>     fix 'missing prototype' error by making function static
>     tried to sort Makefile and Kconfig better
> ---
>  drivers/tty/serial/8250/8250_dfl.c | 149 +++++++++++++++++++++++++++++
>  drivers/tty/serial/8250/Kconfig    |  12 +++
>  drivers/tty/serial/8250/Makefile   |   1 +
>  3 files changed, 162 insertions(+)
>  create mode 100644 drivers/tty/serial/8250/8250_dfl.c
> 
> diff --git a/drivers/tty/serial/8250/8250_dfl.c b/drivers/tty/serial/8250/8250_dfl.c
> new file mode 100644
> index 000000000000..f02f0ba2a565
> --- /dev/null
> +++ b/drivers/tty/serial/8250/8250_dfl.c
> @@ -0,0 +1,149 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Driver for FPGA UART
> + *
> + * Copyright (C) 2022 Intel Corporation, Inc.
> + *
> + * Authors:
> + *   Ananda Ravuri <ananda.ravuri@xxxxxxxxx>
> + *   Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx>
> + */
> +
> +#include <linux/bitfield.h>
> +#include <linux/dfl.h>
> +#include <linux/io-64-nonatomic-lo-hi.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/serial.h>
> +#include <linux/serial_8250.h>
> +
> +struct dfl_uart {
> +	int line;
> +};
> +
> +static int dfl_uart_get_params(struct dfl_device *dfl_dev, struct uart_8250_port *uart)
> +{
> +	struct device *dev = &dfl_dev->dev;
> +	u64 v, fifo_len, reg_width;
> +	u64 *p;
> +
> +	p = dfh_find_param(dfl_dev, DFHv1_PARAM_ID_CLK_FRQ);
> +	if (!p)
> +		return dev_err_probe(dev, -EINVAL, "missing CLK_FRQ param\n");
> +
> +	uart->port.uartclk = *p;
> +	dev_dbg(dev, "UART_CLK_ID %u Hz\n", uart->port.uartclk);
> +
> +	p = dfh_find_param(dfl_dev, DFHv1_PARAM_ID_FIFO_LEN);
> +	if (!p)
> +		return dev_err_probe(dev, -EINVAL, "missing FIFO_LEN param\n");
> +
> +	fifo_len = *p;
> +	dev_dbg(dev, "UART_FIFO_ID fifo_len %llu\n", fifo_len);
> +
> +	switch (fifo_len) {
> +	case 32:
> +		uart->port.type = PORT_ALTR_16550_F32;
> +		break;
> +
> +	case 64:
> +		uart->port.type = PORT_ALTR_16550_F64;
> +		break;
> +
> +	case 128:
> +		uart->port.type = PORT_ALTR_16550_F128;
> +		break;
> +
> +	default:
> +		return dev_err_probe(dev, -EINVAL, "unsupported fifo_len %llu\n", fifo_len);
> +	}
> +
> +	p = dfh_find_param(dfl_dev, DFHv1_PARAM_ID_REG_LAYOUT);
> +	if (!p)
> +		return dev_err_probe(dev, -EINVAL, "missing REG_LAYOUT param\n");
> +
> +	v = *p;
> +	uart->port.regshift = FIELD_GET(DFHv1_PARAM_ID_REG_SHIFT, v);
> +	reg_width = FIELD_GET(DFHv1_PARAM_ID_REG_WIDTH, v);

I have concern that the raw layout inside the parameter block is
still exposed to drivers and need to be parsed by each driver.

How about we define HW agnostic IDs for parameter specific fields like:

PARAM_ID		FIELD_ID
================================
MSIX			STARTV
			NUMV
--------------------------------
CLK			FREQ
--------------------------------
FIFO			LEN
--------------------------------
REG_LAYOUT		WIDTH
			SHIFT

And define like u64 dfl_find_param(struct dfl_device *, int param_id, int field_id)

Think further, if we have to define HW agnostic property - value pairs,
why don't we just use "Software nodes for the firmware node", see
drivers/base/swnode.c. I think this may be a better choice.

Thanks,
Yilun