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From:   Karol Herbst <kherbst@redhat.com>
Date:   Fri, 23 Jul 2021 18:34:39 +0200
Message-ID: <CACO55ttjQO5kUeEA7opvGLAwT+a1t0vAguncKDhB4bdy96K7LA@mail.gmail.com>
Subject: Re: [PATCH] drm/nouveau/kms/nv50-: fix build failure with CONFIG_BACKLIGHT=n
To:     Randy Dunlap <rdunlap@infradead.org>
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>
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On Fri, Jul 23, 2021 at 6:31 PM Randy Dunlap <rdunlap@infradead.org> wrote:
>
> 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.
>

sure, I was just curious if there was a specific use case or just
something random as you mentioned.