linux-kernel - Re: [PATCH] drm/nouveau/backlight: Fix LVDS backlight detection on some laptops

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Date:   Tue, 8 Feb 2022 13:21:12 +0100
From:   Karol Herbst <kherbst@...hat.com>
To:     Lyude Paul <lyude@...hat.com>
Cc:     nouveau <nouveau@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        stable@...r.kernel.org, Ben Skeggs <bskeggs@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/nouveau/backlight: Fix LVDS backlight detection on
 some laptops

On Fri, Feb 4, 2022 at 7:05 PM Lyude Paul <lyude@...hat.com> wrote:
>
> It seems that some laptops will report having both an eDP and LVDS
> connector, even though only the LVDS connector is actually hooked up. This
> can lead to issues with backlight registration if the eDP connector ends up
> getting registered before the LVDS connector, as the backlight device will
> then be registered to the eDP connector instead of the LVDS connector.
>
> So, fix this by only registering the backlight on connectors that are
> reported as being connected.
>

I think the patch might risk breaking muxed systems where we have two
GPUs, but.. the systems I know of have different ways of controlling
the backlight anyway. So unless there is something I missed this is

Reviewed-by: Karol Herbst <kherbst@...hat.com>

> Signed-off-by: Lyude Paul <lyude@...hat.com>
> Fixes: 6eca310e8924 ("drm/nouveau/kms/nv50-: Add basic DPCD backlight support for nouveau")
> Bugzilla: https://gitlab.freedesktop.org/drm/nouveau/-/issues/137
> Cc: <stable@...r.kernel.org> # v5.15+
> ---
>  drivers/gpu/drm/nouveau/nouveau_backlight.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c b/drivers/gpu/drm/nouveau/nouveau_backlight.c
> index ae2f2abc8f5a..6af12dc99d7f 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c
> @@ -294,7 +294,8 @@ nv50_backlight_init(struct nouveau_backlight *bl,
>         struct nouveau_drm *drm = nouveau_drm(nv_encoder->base.base.dev);
>         struct nvif_object *device = &drm->client.device.object;
>
> -       if (!nvif_rd32(device, NV50_PDISP_SOR_PWM_CTL(ffs(nv_encoder->dcb->or) - 1)))
> +       if (!nvif_rd32(device, NV50_PDISP_SOR_PWM_CTL(ffs(nv_encoder->dcb->or) - 1)) ||
> +           nv_conn->base.status != connector_status_connected)
>                 return -ENODEV;
>
>         if (nv_conn->type == DCB_CONNECTOR_eDP) {
> --
> 2.34.1
>