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From:   Daniel Vetter <daniel@ffwll.ch>
Date:   Fri, 23 Jul 2021 11:24:32 +0200
Message-ID: <CAKMK7uHG0T7kgHzrkxoGj+Cv1-5f=GaH1CviunoZd_wEL5G4YQ@mail.gmail.com>
Subject: Re: [PATCH] drm/nouveau/kms/nv50-: fix build failure with CONFIG_BACKLIGHT=n
To:     Arnd Bergmann <arnd@kernel.org>
Cc:     Ben Skeggs <bskeggs@redhat.com>, David Airlie <airlied@linux.ie>,
        Lyude Paul <lyude@redhat.com>, Arnd Bergmann <arnd@arndb.de>,
        =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= <ville.syrjala@linux.intel.com>,
        Nikola Cornij <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>
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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

> ---
>  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
>


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