Re: [PATCH] drm/nouveau/kms/nv50-: fix build failure with CONFIG_BACKLIGHT=n

[Harry Wentland <harry.wentland@amd.com>]

On 2021-07-23 3:14 p.m., Cornij, Nikola wrote:
> [AMD Official Use Only]
> 
> +Harry
> 
> -----Original Message-----
> From: Daniel Vetter <daniel@ffwll.ch>
> Sent: Friday, July 23, 2021 11:23 AM
> To: Arnd Bergmann <arnd@kernel.org>
> Cc: Daniel Vetter <daniel@ffwll.ch>; Ben Skeggs <bskeggs@redhat.com>; David Airlie <airlied@linux.ie>; Lyude Paul <lyude@redhat.com>; Arnd Bergmann <arnd@arndb.de>; Ville Syrjälä <ville.syrjala@linux.intel.com>; Cornij, Nikola <Nikola.Cornij@amd.com>; dri-devel <dri-devel@lists.freedesktop.org>; Nouveau Dev <nouveau@lists.freedesktop.org>; Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
> Subject: Re: [PATCH] drm/nouveau/kms/nv50-: fix build failure with CONFIG_BACKLIGHT=n
> 
> On Fri, Jul 23, 2021 at 12:16:31PM +0200, Arnd Bergmann wrote:
>> On Fri, Jul 23, 2021 at 11:25 AM Daniel Vetter <daniel@ffwll.ch> wrote:
>>>
>>> On Fri, Jul 23, 2021 at 11:15 AM Arnd Bergmann <arnd@kernel.org> wrote:
>>>>
>>>> From: Arnd Bergmann <arnd@arndb.de>
>>>>
>>>> When the backlight support is disabled, the driver fails to build:
>>>>
>>>> drivers/gpu/drm/nouveau/dispnv50/disp.c: In function 'nv50_sor_atomic_disable':
>>>> drivers/gpu/drm/nouveau/dispnv50/disp.c:1665:59: error: 'struct nouveau_connector' has no member named 'backlight'
>>>>  1665 |         struct nouveau_backlight *backlight = nv_connector->backlight;
>>>>       |                                                           ^~
>>>> drivers/gpu/drm/nouveau/dispnv50/disp.c:1670:35: error: invalid use of undefined type 'struct nouveau_backlight'
>>>>  1670 |         if (backlight && backlight->uses_dpcd) {
>>>>       |                                   ^~
>>>> drivers/gpu/drm/nouveau/dispnv50/disp.c:1671:64: error: invalid use of undefined type 'struct nouveau_backlight'
>>>>  1671 |                 ret = drm_edp_backlight_disable(aux, &backlight->edp_info);
>>>>       |                                                                ^~
>>>>
>>>> The patch that introduced the problem already contains some #ifdef
>>>> checks, so just add another one that makes it build again.
>>>>
>>>> Fixes: 6eca310e8924 ("drm/nouveau/kms/nv50-: Add basic DPCD
>>>> backlight support for nouveau")
>>>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>>>
>>> Can we just toss the idea that BACKTLIGHT=n is a reasonable config
>>> for drm drivers using backlights, and add depends BACKLIGHT to all
>>> of them?
>>>
>>> I mean this is a perfect source of continued patch streams to keep
>>> us all busy, but beyond that I really don't see the point ... I
>>> frankly have better things to do, and especially with the big
>>> drivers we have making backlight optional saves comparitively nothing.
>>> -Daniel
>>
>> Yes! I'd definitely be in favor of that, I've wasted way too much time
>> trying to sort through dependency loops and other problems with backlight support.
>>
>> Maybe we should leave the drivers/video/fbdev/ drivers untouched in
>> this regard, at least for the moment, but for the drivers/gpu/drm
>> users of backlight that would be a nice simplification, and even the
>> smallest ones are unlikely to be used on systems that are too memory
>> constrained to deal with 4KB extra .text.
> 
> Yeah I think we can do this entirely ad-hoc, i.e. any time the backlight wheel wobbles off again we nail it down for good for that driver with a depends on BACKGLIGHT and remove any lingering #ifdef all over.
> 
> If you want maybe start out with the biggest drm drivers in a series, I think if nouveau/amdgpu/i915 folks ack this you're good to go to just convert as things get in the way.

Sounds like a good idea to me.

Harry

> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch/>>