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

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Date:   Fri,  4 Feb 2022 13:05:04 -0500
From:   Lyude Paul <lyude@...hat.com>
To:     nouveau@...ts.freedesktop.org
Cc:     dri-devel@...ts.freedesktop.org, stable@...r.kernel.org,
        Ben Skeggs <bskeggs@...hat.com>,
        Karol Herbst <kherbst@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        linux-kernel@...r.kernel.org (open list)
Subject: [PATCH] drm/nouveau/backlight: Fix LVDS backlight detection on some laptops

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.

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