Re: [PATCH v3 4/4] tty: serial: 8250: add DFL bus driver for Altera 16550.

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Tue, Oct 04, 2022 at 07:37:18AM -0700, matthew.gerlach@linux.intel.com wrote:
> From: Matthew Gerlach <matthew.gerlach@linux.intel.com>
> 
> Add a Device Feature List (DFL) bus driver for the Altera
> 16550 implementation of UART.

...

> Reported-by: kernel test robot <lkp@intel.com>

https://docs.kernel.org/process/submitting-patches.html?highlight=reported#using-reported-by-tested-by-reviewed-by-suggested-by-and-fixes

"The Reported-by tag gives credit to people who find bugs and report them and it
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feature requests."


...

> +	if (!dfhv1_has_params(dfh_base)) {
> +		dev_err(dev, "missing required DFH parameters\n");
> +		return -EINVAL;
> +	}

Why not use dev_err_probe() everywhere since this is called only at ->probe()
stage?

...

> +	off = dfhv1_find_param(dfh_base, max, DFHv1_PARAM_ID_CLK_FRQ);
> +	if (off < 0) {
> +		dev_err(dev, "missing CLK_FRQ param\n");

> +		return -EINVAL;

Why error code is being shadowed?

> +	}

...

> +	off = dfhv1_find_param(dfh_base, max, DFHv1_PARAM_ID_FIFO_LEN);
> +	if (off < 0) {
> +		dev_err(dev, "missing FIFO_LEN param\n");
> +		return -EINVAL;

Ditto.

> +	}

...

> +	off = dfhv1_find_param(dfh_base, max, DFHv1_PARAM_ID_REG_LAYOUT);
> +	if (off < 0) {
> +		dev_err(dev, "missing REG_LAYOUT param\n");
> +		return -EINVAL;
> +	}

Ditto.

...

> +	dev_dbg(dev, "UART_LAYOUT_ID width %lld shift %d\n",
> +		FIELD_GET(DFHv1_PARAM_ID_REG_WIDTH, v), (int)uart->port.regshift);

Casting in printf() in kernel in 99% shows the wrong specifier in use. Try to
select the best suitable one.

...

> +	dfh_base = devm_ioremap_resource(dev, &dfl_dev->mmio_res);
> +	if (IS_ERR(dfh_base))
> +		return PTR_ERR(dfh_base);
> +
> +	res_size = resource_size(&dfl_dev->mmio_res);
> +
> +	ret = dfl_uart_get_params(dev, dfh_base, res_size, &uart);

> +	devm_iounmap(dev, dfh_base);
> +	devm_release_mem_region(dev, dfl_dev->mmio_res.start, res_size);

If it's temporary, may be you shouldn't even consider devm_ioremap_resource()
to begin with? The devm_* release type of functions in 99% of the cases
indicate of the abusing devm_.

> +	if (ret < 0)
> +		return dev_err_probe(dev, ret, "failed uart feature walk\n");

...

> +	dev_info(dev, "serial8250_register_8250_port %d\n", dfluart->line);

Why do we need this noise?

...

> +	if (dfluart->line >= 0)

When this can be false?

> +		serial8250_unregister_port(dfluart->line);

...

> +config SERIAL_8250_DFL
> +	tristate "DFL bus driver for Altera 16550 UART"
> +	depends on SERIAL_8250 && FPGA_DFL
> +	help
> +	  This option enables support for a Device Feature List (DFL) bus
> +	  driver for the Altera 16650 UART.  One or more Altera 16650 UARTs
> +	  can be instantiated in a FPGA and then be discovered during
> +	  enumeration of the DFL bus.

When m, what be the module name?

...

>  obj-$(CONFIG_SERIAL_8250_FOURPORT)	+= 8250_fourport.o
>  obj-$(CONFIG_SERIAL_8250_ACCENT)	+= 8250_accent.o
>  obj-$(CONFIG_SERIAL_8250_BOCA)		+= 8250_boca.o
> +obj-$(CONFIG_SERIAL_8250_DFL)		+= 8250_dfl.o

This group of drivers for the 4 UARTs on the board or so, does FPGA belong to
it? (Same Q, btw, for the Kconfig section. And yes, I know that some of the
entries are not properly placed there and in Makefile.)

>  obj-$(CONFIG_SERIAL_8250_EXAR_ST16C554)	+= 8250_exar_st16c554.o
>  obj-$(CONFIG_SERIAL_8250_HUB6)		+= 8250_hub6.o
>  obj-$(CONFIG_SERIAL_8250_FSL)		+= 8250_fsl.o

-- 
With Best Regards,
Andy Shevchenko