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

[matthew . gerlach]

On Tue, 4 Oct 2022, Andy Shevchenko wrote:

> On Tue, Oct 04, 2022 at 07:37:18AM -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.
>
> ...
>
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
>
> 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
> hopefully inspires them to help us again in the future. Please note that if the
> bug was reported in private, then ask for permission first before using the
> Reported-by tag. The tag is intended for bugs; please do not use it to credit
> feature requests."

The kernel test robot did find a bug in my v1 submission.  I was missing 
the static keyword for a function declaration.  Should I remove the tag?

> ...
>
> > +	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?

I wasn't sure if using dev_err_probe() was correct, since the usage is 
technically in a different function.  Since the code is only called from 
->probe(), and it is much cleaner, I'll switch to dev_err_probe() 
everywhere

> > ...
>
> > +	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?

Definitely a mistake.

> > +	}
>
> ...
>
> > +	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.

I will remove the casting and find the correct format specifier.

> ...
>
> > +	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_.

I will change the code to call ioremap() and request_mem_region() directly 
instead of the devm_ versions.

> > +	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?

No, we do not need this noise.

> ...
>
> > +	if (dfluart->line >= 0)
>
> When this can be false?

This can never be false.  I will remove it.

> > +		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?

I see the file, kernel/drivers/tty/serial/8250/8250_dfl.ko, installed 
into /lib/modules/...  I also see "alias dfl:t0000f0024* 8250_dfl" in 
modules.alias


> ...
>
> >  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.)

Since 8250_dfl results in its own module, and my kernel config doesn't 
have FOURPORT, ACCENT, nor BOCA, I guess I don't understand the problem.

> >  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

Thanks for the feedback.


>