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

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Message-ID: <alpine.DEB.2.22.394.2210070807340.2155700@rhweight-WRK1>
Date:   Fri, 7 Oct 2022 08:10:34 -0700 (PDT)
From:   matthew.gerlach@...ux.intel.com
To:     Andy Shevchenko <andriy.shevchenko@...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 Fri, 7 Oct 2022, Andy Shevchenko wrote:

> 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.

In the Kconfig, I think the driver fits into the section, Misc. 
options/drivers.  Within this section, I think SERIAL_8250_DFL should go 
before SERIAL_8250_DW to approximate alphabetical ordering.  Similarly, I 
think 8250_dfl.o should go above 8250_dw.o in the 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
>
>
>