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

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Message-ID: <Yz/uTGeNaOP4Btli@smile.fi.intel.com>
Date:   Fri, 7 Oct 2022 12:15:56 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     matthew.gerlach@...ux.intel.com
Cc:     hao.wu@...el.com, yilun.xu@...el.com, russell.h.weight@...el.com,
        basheer.ahmed.muddebihal@...el.com, trix@...hat.com,
        mdf@...nel.org, linux-fpga@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        tianfei.zhang@...el.com, corbet@....net,
        gregkh@...uxfoundation.org, linux-serial@...r.kernel.org,
        jirislaby@...nel.org, geert+renesas@...der.be,
        niklas.soderlund+renesas@...natech.se, macro@...am.me.uk,
        johan@...nel.org, lukas@...ner.de,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v3 4/4] tty: serial: 8250: add DFL bus driver for Altera
 16550.

On Thu, Oct 06, 2022 at 03:24:16PM -0700, matthew.gerlach@...ux.intel.com wrote:
> On Thu, 6 Oct 2022, Andy Shevchenko wrote:
> > On Thu, Oct 06, 2022 at 10:00:43AM -0700, matthew.gerlach@...ux.intel.com wrote:
> > > On Tue, 4 Oct 2022, Andy Shevchenko wrote:
> > > > On Tue, Oct 04, 2022 at 07:37:18AM -0700, matthew.gerlach@...ux.intel.com wrote:

...

> > > > > Reported-by: kernel test robot <lkp@...el.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
> > > > 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?
> > 
> > What's yours take from the above documentation?
> 
> Since the kernel test robot did find a bug. The tag should stay.

I suggest otherwise because of the last sentence in the cited excerpt: "please
do not use it to credit feature requests". To distinguish "feature request" you
can ask yourself "Am I fixing _existing_ code or adding a new one?" And the
answer here is crystal clear (at least to me).

...

> > > > > +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
> > 
> > My point is that user who will run `make menuconfig` will read this and have
> > no clue after the kernel build if the module was built or not. Look into other
> > (recent) sections of the Kconfig for drivers in the kernel for how they inform
> > user about the module name (this more or less standard pattern you just need
> > to copy'n'paste'n'edit carefully).
> 
> I think this should be added:
>           To compile this driver as a module, chose M here: the
>           module will be called 8250_dfl.

Looks good to me!


> > > > >  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.
> > 
> > The Makefile is a bit chaotic, but try to find the sorted (more or less)
> > group of drivers that are not 4 ports and squeeze your entry there
> > (I expect somewhere between the LPSS/MID lines).
> > 
> > It will help to sort out that mess in the future.
> 
> I will move 8250_dfl between LPSS and MID lines in the Makefile.  Should I
> move the definition in Kconfig to be between LPSS and MID to be consistent?

D is not ordered if put between L and M, I meant not to literally put it there
but think about it a bit.

Kconfig is another story because it has different approach in ordering (seems
so), try to find the best compromise there.

> > > > >  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