Re: [PATCH] drm/pl111: add ARM_AMBA dependency

[Arnd Bergmann]

On Mon, May 22, 2017 at 6:23 PM, Eric Anholt <eric@xxxxxxxxxx> wrote:
> Arnd Bergmann <arnd@xxxxxxxx> writes:
>
>> The driver is written in a way to enable compile-testing without CONFIG_ARM_AMBA,
>> but it just causes needless warnings:
>>
>> drivers/gpu/drm/pl111/pl111_drv.c:149:26: error: 'pl111_drm_driver' defined but not used [-Werror=unused-variable]
>> drivers/gpu/drm/pl111/pl111_drv.c:81:12: error: 'pl111_modeset_init' defined but not used [-Werror=unused-function]
>>
>> This removes the #ifdef instead, and adds a dependency on ARM_AMBA to
>> only let us build the driver when the base support is enabled.
>>
>> Unfortunately, this requires removing one redundant 'select ARM_AMBA'
>> line from mach-s3c64xx to avoid a circular dependency.
>>
>> It might be good to allow manually enabling ARM_AMBA when COMPILE_TEST
>> is turned on, but that should be a separate patch and may cause other
>> build regressions.
>
> If I understand the Kconfig, you're effectively disabling the build on
> COMPILE_TEST && !ARM.  I'd rather that we just fix up the warnings, so
> that people can keep build-testing DRM drivers:
>
> https://patchwork.kernel.org/patch/9737857/

That works too. When I tried the same, I thought it was a little too silly to
have a file that effectively compiles into nothing.

My initial approach did two things differently though:

- use __maybe_unused instead of __used, since

- annotate pl111_amba_driver instead of
  pl111_drm_driver/pl111_modeset_init, and keep only
  module_amba_driver() in the #ifdef.

       Arnd