[Intel-gfx] [PATCH v4 12/31] drm/nouveau: Register ACPI video backlight when nv_backlight registration fails (v2)

Hans de Goede
2022-08-24T12:18:09Z

Typically the acpi_video driver will initialize before nouveau, which
used to cause /sys/class/backlight/acpi_video0 to get registered and then
nouveau would register its own nv_backlight device later. After which
the drivers/acpi/video_detect.c code unregistered the acpi_video0 device
to avoid there being 2 backlight devices.

This means that userspace used to briefly see 2 devices and the
disappearing of acpi_video0 after a brief time confuses the systemd
backlight level save/restore code, see e.g.:
https://bbs.archlinux.org/viewtopic.php?id=269920

To fix this the ACPI video code has been modified to make backlight class
device registration a separate step, relying on the drm/kms driver to
ask for the acpi_video backlight registration after it is done setting up
its native backlight device.

Add a call to the new acpi_video_register_backlight() when native backlight
device registration has failed / was skipped to ensure that there is a
backlight device available before the drm_device gets registered with
userspace.

Changes in v2:
- Add nouveau_acpi_video_register_backlight() wrapper to avoid unresolved
symbol errors on non X86

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
drivers/gpu/drm/nouveau/nouveau_acpi.c | 5 +++++
drivers/gpu/drm/nouveau/nouveau_acpi.h | 2 ++
drivers/gpu/drm/nouveau/nouveau_backlight.c | 7 +++++++
3 files changed, 14 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.c b/drivers/gpu/drm/nouveau/nouveau_acpi.c
index 1592c9cd7750..8cf096f841a9 100644
--- a/drivers/gpu/drm/nouveau/nouveau_acpi.c
+++ b/drivers/gpu/drm/nouveau/nouveau_acpi.c
@@ -391,3 +391,8 @@ bool nouveau_acpi_video_backlight_use_native(void)
{
return acpi_video_backlight_use_native();
}
+
+void nouveau_acpi_video_register_backlight(void)
+{
+ acpi_video_register_backlight();
+}
diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.h b/drivers/gpu/drm/nouveau/nouveau_acpi.h
index 3c666c30dfca..e39dd8b94b8b 100644
--- a/drivers/gpu/drm/nouveau/nouveau_acpi.h
+++ b/drivers/gpu/drm/nouveau/nouveau_acpi.h
@@ -12,6 +12,7 @@ void nouveau_unregister_dsm_handler(void);
void nouveau_switcheroo_optimus_dsm(void);
void *nouveau_acpi_edid(struct drm_device *, struct drm_connector *);
bool nouveau_acpi_video_backlight_use_native(void);
+void nouveau_acpi_video_register_backlight(void);
#else
static inline bool nouveau_is_optimus(void) { return false; };
static inline bool nouveau_is_v1_dsm(void) { return false; };
@@ -20,6 +21,7 @@ static inline void nouveau_unregister_dsm_handler(void) {}
static inline void nouveau_switcheroo_optimus_dsm(void) {}
static inline void *nouveau_acpi_edid(struct drm_device *dev, struct drm_connector *connector) { return NULL; }
static inline bool nouveau_acpi_video_backlight_use_native(void) { return true; }
+static inline void nouveau_acpi_video_register_backlight(void) {}
#endif

#endif
diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c b/drivers/gpu/drm/nouveau/nouveau_backlight.c
index d2b8f8c13db4..a614582779ca 100644
--- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
+++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c
@@ -436,6 +436,13 @@ nouveau_backlight_init(struct drm_connector *connector)

fail_alloc:
kfree(bl);
+ /*
+ * If we get here we have an internal panel, but no nv_backlight,
+ * try registering an ACPI video backlight device instead.
+ */
+ if (ret == 0)
+ nouveau_acpi_video_register_backlight();
+
return ret;
}

--
2.37.2