linux-kernel - Re: [PATCH] drm/nouveau/kms/nv50-: fix build failure with CONFIG

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Date:   Fri, 23 Jul 2021 12:12:47 -0400
From:   Lyude Paul <lyude@...hat.com>
To:     Daniel Vetter <daniel@...ll.ch>, Arnd Bergmann <arnd@...nel.org>
Cc:     Ben Skeggs <bskeggs@...hat.com>, David Airlie <airlied@...ux.ie>,
        Arnd Bergmann <arnd@...db.de>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Nikola Cornij <nikola.cornij@....com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Nouveau Dev <nouveau@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/nouveau/kms/nv50-: fix build failure with
 CONFIG_BACKLIGHT=n

On Fri, 2021-07-23 at 11:24 +0200, Daniel Vetter wrote:
> On Fri, Jul 23, 2021 at 11:15 AM Arnd Bergmann <arnd@...nel.org> wrote:
> > 
> > From: Arnd Bergmann <arnd@...db.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@...db.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?

Yeah - I'm fine with this IMHO, at least for the drivers actually supporting
backlights in some manner (I assume this is most of them though)

> 
> 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
> 
> > ---
> >  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);
> > --
> > 2.29.2
> > 
> 
> 

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat