[PATCH v2 11/29] drm/i915: Call acpi_video_register_backlight() (v2)

[Hans de Goede <hdegoede@redhat.com>]

On machins without an i915 opregion the acpi_video driver immediately
probes the ACPI video bus and used to also immediately register
acpi_video# backlight devices when supported.

Once the drm/kms driver then loaded later and possibly registered
a native backlight device then the drivers/acpi/video_detect.c code
unregistered the acpi_video0 device to avoid there being 2 backlight
devices (when acpi_video_get_backlight_type()==native).

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() after the i915 calls
acpi_video_register() (after setting up the i915 opregion) so that the
acpi_video backlight devices get registered on systems where the i915
native backlight device is not registered.

Changes in v2:
-Only call acpi_video_register_backlight() when a panel is detected

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/gpu/drm/i915/display/intel_display.c | 8 ++++++++
 drivers/gpu/drm/i915/display/intel_panel.c   | 3 +++
 drivers/gpu/drm/i915/i915_drv.h              | 2 ++
 3 files changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index a0f84cbe974f..6e120de83c0f 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -9086,6 +9086,14 @@ void intel_display_driver_register(struct drm_i915_private *i915)
 	/* Must be done after probing outputs */
 	intel_opregion_register(i915);
 	acpi_video_register();
+	/*
+	 * Only call this if i915 is driving the internal panel. If the internal
+	 * panel is not driven by i915 then another GPU driver may still register
+	 * a native backlight driver later and this should only be called after
+	 * any native backlights have been registered.
+	 */
+	if (i915->have_panel)
+		acpi_video_register_backlight();
 
 	intel_audio_init(i915);
 
diff --git a/drivers/gpu/drm/i915/display/intel_panel.c b/drivers/gpu/drm/i915/display/intel_panel.c
index 237a40623dd7..4536c527f50c 100644
--- a/drivers/gpu/drm/i915/display/intel_panel.c
+++ b/drivers/gpu/drm/i915/display/intel_panel.c
@@ -646,8 +646,11 @@ intel_panel_mode_valid(struct intel_connector *connector,
 
 int intel_panel_init(struct intel_connector *connector)
 {
+	struct drm_i915_private *dev_priv = to_i915(connector->base.dev);
 	struct intel_panel *panel = &connector->panel;
 
+	dev_priv->have_panel = true;
+
 	intel_backlight_init_funcs(panel);
 
 	drm_dbg_kms(connector->base.dev,
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index d25647be25d1..be6e8c6d8f73 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -756,6 +756,8 @@ struct drm_i915_private {
 
 	bool ipc_enabled;
 
+	bool have_panel;
+
 	struct intel_audio_private audio;
 
 	struct i915_pmu pmu;
-- 
2.36.0