drm/nouveau/kms: Fix backlight registration

The nouveau code used to call drm_fb_helper_initial_config() from
nouveau_fbcon_init() before calling drm_dev_register(). This would
probe all connectors so that drm_connector->status could be used during
backlight registration which runs from nouveau_connector_late_register().

After commit 4a16dd9d18a0 ("drm/nouveau/kms: switch to drm fbdev helpers")
the fbdev emulation code, which now is a drm-client, can only run after
drm_dev_register(). So during backlight registration the connectors are
not probed yet and the drm_connector->status == connected check in
nv50_backlight_init() would now always fail.

Replace the drm_connector->status == connected check with
a drm_helper_probe_detect() == connected check to fix nv_backlight
no longer getting registered because of this.

Fixes: 4a16dd9d18a0 ("drm/nouveau/kms: switch to drm fbdev helpers")
Link: https://gitlab.freedesktop.org/drm/nouveau/-/issues/202
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2181941
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230326205433.36485-1-hdegoede@redhat.com

diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c b/drivers/gpu/drm/nouveau/nouveau_backlight.c
index 40409a2..91b5ecc 100644 (file)
--- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
+++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c
@@ -33,6 +33,7 @@
 #include <linux/apple-gmux.h>
 #include <linux/backlight.h>
 #include <linux/idr.h>
+#include <drm/drm_probe_helper.h>
 
 #include "nouveau_drv.h"
 #include "nouveau_reg.h"
@@ -299,8 +300,12 @@ 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;
 
+       /*
+        * Note when this runs the connectors have not been probed yet,
+        * so nv_conn->base.status is not set yet.
+        */
        if (!nvif_rd32(device, NV50_PDISP_SOR_PWM_CTL(ffs(nv_encoder->dcb->or) - 1)) ||
-           nv_conn->base.status != connector_status_connected)
+           drm_helper_probe_detect(&nv_conn->base, NULL, false) != connector_status_connected)
                return -ENODEV;
 
        if (nv_conn->type == DCB_CONNECTOR_eDP) {