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Subject: Re: [PATCH] drm/nouveau/kms/nv50-: fix build failure with
 CONFIG_BACKLIGHT=n
To:     Karol Herbst <kherbst@redhat.com>
Cc:     Arnd Bergmann <arnd@kernel.org>, Ben Skeggs <bskeggs@redhat.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>, Lyude Paul <lyude@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>,
        nouveau <nouveau@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Nikola Cornij <nikola.cornij@amd.com>
References: <20210723091534.1730564-1-arnd@kernel.org>
 <a618e29a-e4b7-bda4-a3e0-7dfd67d64e92@infradead.org>
 <CACO55tvQoCnjQWRJhrJ+8TzY5MuDDSUSnwd5AU8G1qsQYCSCBg@mail.gmail.com>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <7ddd0c7c-9bdc-9ea3-c635-f1d141d1e870@infradead.org>
Date:   Fri, 23 Jul 2021 09:31:34 -0700
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On 7/23/21 8:15 AM, Karol Herbst wrote:
> On Fri, Jul 23, 2021 at 5:10 PM Randy Dunlap <rdunlap@infradead.org> wrote:
>>
>> On 7/23/21 2:15 AM, Arnd Bergmann 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>
>>> ---
>>>  drivers/gpu/drm/nouveau/dispnv50/disp.c | 11 +++++++----
>>>  1 file changed, 7 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/nouveau/dispnv50/disp.c b/drivers/gpu/drm/nouveau/dispnv50/disp.c
>>> index 093e1f7163b3..fcf53e24db21 100644
>>> --- a/drivers/gpu/drm/nouveau/dispnv50/disp.c
>>> +++ b/drivers/gpu/drm/nouveau/dispnv50/disp.c
>>> @@ -1659,20 +1659,23 @@ static void
>>>  nv50_sor_atomic_disable(struct drm_encoder *encoder, struct drm_atomic_state *state)
>>>  {
>>>       struct nouveau_encoder *nv_encoder = nouveau_encoder(encoder);
>>> -     struct nouveau_drm *drm = nouveau_drm(nv_encoder->base.base.dev);
>>>       struct nouveau_crtc *nv_crtc = nouveau_crtc(nv_encoder->crtc);
>>>       struct nouveau_connector *nv_connector = nv50_outp_get_old_connector(state, nv_encoder);
>>> -     struct nouveau_backlight *backlight = nv_connector->backlight;
>>>       struct drm_dp_aux *aux = &nv_connector->aux;
>>> -     int ret;
>>>       u8 pwr;
>>>
>>> +#ifdef CONFIG_DRM_NOUVEAU_BACKLIGHT
>>> +     struct nouveau_drm *drm = nouveau_drm(nv_encoder->base.base.dev);
>>> +     struct nouveau_backlight *backlight = nv_connector->backlight;
>>> +
>>>       if (backlight && backlight->uses_dpcd) {
>>> -             ret = drm_edp_backlight_disable(aux, &backlight->edp_info);
>>> +             int ret = drm_edp_backlight_disable(aux, &backlight->edp_info);
>>> +
>>>               if (ret < 0)
>>>                       NV_ERROR(drm, "Failed to disable backlight on [CONNECTOR:%d:%s]: %d\n",
>>>                                nv_connector->base.base.id, nv_connector->base.name, ret);
>>>       }
>>> +#endif
>>>
>>>       if (nv_encoder->dcb->type == DCB_OUTPUT_DP) {
>>>               int ret = drm_dp_dpcd_readb(aux, DP_SET_POWER, &pwr);
>>>
>>
>> Hm, only Lyude Paul replied to this patch:
>>
>> https://lore.kernel.org/lkml/20210714171523.413-1-rdunlap@infradead.org/
>>
> 
> what's actually the use case of compiling with
> CONFIG_DRM_NOUVEAU_BACKLIGHT=n anyway?

Dunno. In this case it was just a randconfig. Still, it needs to be
handled in some way - such as the other suggestion in this thread.