linux-kernel - Re: [PATCH v3] firmware: coreboot: Don't register a pdev if screen

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Message-ID: <a6a994b0-5021-49e5-b853-a1b2abe3af2f@suse.de>
Date: Mon, 16 Sep 2024 10:59:51 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Javier Martinez Canillas <javierm@...hat.com>,
 kernel test robot <lkp@...el.com>, linux-kernel@...r.kernel.org
Cc: llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
 Julius Werner <jwerner@...omium.org>, Hugues Bruant
 <hugues.bruant@...il.com>, intel-gfx@...ts.freedesktop.org,
 Brian Norris <briannorris@...omium.org>, dri-devel@...ts.freedesktop.org,
 Borislav Petkov <bp@...en8.de>, chrome-platform@...ts.linux.dev,
 Tzung-Bi Shih <tzungbi@...nel.org>
Subject: Re: [PATCH v3] firmware: coreboot: Don't register a pdev if
 screen_info data is present

Hi Javier

Am 16.09.24 um 10:36 schrieb Javier Martinez Canillas:
> Thomas Zimmermann <tzimmermann@...e.de> writes:
>
> Hello Thomas and Tzung-Bi,
>
>> Hi
>>
>> Am 15.09.24 um 09:44 schrieb kernel test robot:
>>> Hi Javier,
>>>
>>> kernel test robot noticed the following build errors:
>>>
>>> [auto build test ERROR on chrome-platform/for-next]
>>> [also build test ERROR on chrome-platform/for-firmware-next linus/master v6.11-rc7 next-20240913]
>>> [If your patch is applied to the wrong git tree, kindly drop us a note.
>>> And when submitting patch, we suggest to use '--base' as documented in
>>> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>>>
>>> url:    https://github.com/intel-lab-lkp/linux/commits/Javier-Martinez-Canillas/firmware-coreboot-Don-t-register-a-pdev-if-screen_info-data-is-present/20240914-053323
>>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/chrome-platform/linux.git for-next
>>> patch link:    https://lore.kernel.org/r/20240913213246.1549213-1-javierm%40redhat.com
>>> patch subject: [PATCH v3] firmware: coreboot: Don't register a pdev if screen_info data is present
>>> config: riscv-randconfig-001-20240915 (https://download.01.org/0day-ci/archive/20240915/202409151528.CIWZRPBq-lkp@intel.com/config)
>>> compiler: clang version 15.0.7 (https://github.com/llvm/llvm-project 8dfdcc7b7bf66834a761bd8de445840ef68e4d1a)
>>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240915/202409151528.CIWZRPBq-lkp@intel.com/reproduce)
>>>
>>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>>> the same patch/commit), kindly add following tags
>>> | Reported-by: kernel test robot <lkp@...el.com>
>>> | Closes: https://lore.kernel.org/oe-kbuild-all/202409151528.CIWZRPBq-lkp@intel.com/
>>>
>>> All errors (new ones prefixed by >>):
>>>
>>>>> ld.lld: error: undefined symbol: screen_info
>>>      >>> referenced by framebuffer-coreboot.c:27 (drivers/firmware/google/framebuffer-coreboot.c:27)
>>>      >>>               drivers/firmware/google/framebuffer-coreboot.o:(framebuffer_probe) in archive vmlinux.a
>>>      >>> referenced by framebuffer-coreboot.c:27 (drivers/firmware/google/framebuffer-coreboot.c:27)
>>>      >>>               drivers/firmware/google/framebuffer-coreboot.o:(framebuffer_probe) in archive vmlinux.a
>> Not all platforms define screen_info. Maybe fix this by following
> Yes, after reading the build errors reported by the robot I remembered
> that we had similar issues with sysfb, for example commit 1260b9a7020
> ("drivers/firmware: fix SYSFB depends to prevent build failures") fixed
> one of those.
>
>> Tzung-Bi's advice of removing the local variables and then guard the
>> test by CONFIG_SYSFB. If SYSFB has been defined, screen_info has to be
>> there. It's not a super pretty solution, though.
>>
> If possible I would prefer to avoid the ifdefery in the driver. I also
> believe that the local variables makes the code easier to read. But if
> you folks think that's better to drop them, I can do it in the next rev.
>
> Another option is to restrict the architectures where this driver could
> be build. As far as I understand it is mainly for x86 and ARM64 arches.
>
> These two have a screen_info defined so the driver will build correctly.
> I can include a preparatory patch that adds a "depends on x86 || ARM64".

That feels arbitrary, as the dependency is not really in coreboot, but 
in sysbf. What you'd want is a HAVE_SCREEN_INFO define on the 
architectures that provide it. IIRC earlier attempts to add this have 
failed. :/

If you don't want the ifdef-ery in coreboot.c, you could add a helper to 
sysfb. Let's say

   bool sysfb_handles_screen_info(void)

returns the result of the test. If you put it next to sysfb_disable(), 
you could add an empty wrapper into the sysfb.h header as well. [1]

(There's still the possibility that screen_info is available, but sysfb 
has been disabled. But that's not different from how it currently works.)

[1] 
https://elixir.bootlin.com/linux/v6.10.10/source/include/linux/sysfb.h#L65

Best regards
Thomas

>
>> Best regards
>> Thomas
>>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)