[PATCH v4 01/31] ACPI: video: Add acpi_video_backlight_use_native() helper

Hans de Goede
2022-08-24T12:15:52Z

ATM on x86 laptops where we want userspace to use the acpi_video backlight
device we often register both the GPU's native backlight device and
acpi_video's firmware acpi_video# backlight device. This relies on
userspace preferring firmware type backlight devices over native ones, but
registering 2 backlight devices for a single display really is undesirable.

On x86 laptops where the native GPU backlight device should be used,
the registering of other backlight devices is avoided by their drivers
using acpi_video_get_backlight_type() and only registering their backlight
if the return value matches their type.

acpi_video_get_backlight_type() uses
backlight_device_get_by_type(BACKLIGHT_RAW) to determine if a native
driver is available and will never return native if this returns
false. This means that the GPU's native backlight registering code
cannot just call acpi_video_get_backlight_type() to determine if it
should register its backlight, since acpi_video_get_backlight_type() will
never return native until the native backlight has already registered.

To fix this add a new internal native function parameter to
acpi_video_get_backlight_type(), which when set to true will make
acpi_video_get_backlight_type() behave as if a native backlight has
already been registered.

And add a new acpi_video_backlight_use_native() helper, which sets this
to true, for use in native GPU backlight code.

Changes in v2:
- Replace adding a native parameter to acpi_video_get_backlight_type() with
adding a new acpi_video_backlight_use_native() helper.

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
drivers/acpi/video_detect.c | 24 ++++++++++++++++++++----
include/acpi/video.h | 5 +++++
2 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
index 5d7f38016a24..5f105eaa7d30 100644
--- a/drivers/acpi/video_detect.c
+++ b/drivers/acpi/video_detect.c
@@ -17,8 +17,9 @@
* Otherwise vendor specific drivers like thinkpad_acpi, asus-laptop,
* sony_acpi,... can take care about backlight brightness.
*
- * Backlight drivers can use acpi_video_get_backlight_type() to determine
- * which driver should handle the backlight.
+ * Backlight drivers can use acpi_video_get_backlight_type() to determine which
+ * driver should handle the backlight. RAW/GPU-driver backlight drivers must
+ * use the acpi_video_backlight_use_native() helper for this.
*
* If CONFIG_ACPI_VIDEO is neither set as "compiled in" (y) nor as a module (m)
* this file will not be compiled and acpi_video_get_backlight_type() will
@@ -571,9 +572,10 @@ static int acpi_video_backlight_notify(struct notifier_block *nb,
* Arguably the native on win8 check should be done first, but that would
* be a behavior change, which may causes issues.
*/
-enum acpi_backlight_type acpi_video_get_backlight_type(void)
+static enum acpi_backlight_type __acpi_video_get_backlight_type(bool native)
{
static DEFINE_MUTEX(init_mutex);
+ static bool native_available;
static bool init_done;
static long video_caps;

@@ -593,6 +595,8 @@ enum acpi_backlight_type acpi_video_get_backlight_type(void)
backlight_notifier_registered = true;
init_done = true;
}
+ if (native)
+ native_available = true;
mutex_unlock(&init_mutex);

if (acpi_backlight_cmdline != acpi_backlight_undef)
@@ -604,13 +608,25 @@ enum acpi_backlight_type acpi_video_get_backlight_type(void)
if (!(video_caps & ACPI_VIDEO_BACKLIGHT))
return acpi_backlight_vendor;

- if (acpi_osi_is_win8() && backlight_device_get_by_type(BACKLIGHT_RAW))
+ if (acpi_osi_is_win8() &&
+ (native_available || backlight_device_get_by_type(BACKLIGHT_RAW)))
return acpi_backlight_native;

return acpi_backlight_video;
}
+
+enum acpi_backlight_type acpi_video_get_backlight_type(void)
+{
+ return __acpi_video_get_backlight_type(false);
+}
EXPORT_SYMBOL(acpi_video_get_backlight_type);

+bool acpi_video_backlight_use_native(void)
+{
+ return __acpi_video_get_backlight_type(true) == acpi_backlight_native;
+}
+EXPORT_SYMBOL(acpi_video_backlight_use_native);
+
/*
* Set the preferred backlight interface type based on DMI info.
* This function allows DMI blacklists to be implemented by external
diff --git a/include/acpi/video.h b/include/acpi/video.h
index db8548ff03ce..4705e339c252 100644
--- a/include/acpi/video.h
+++ b/include/acpi/video.h
@@ -56,6 +56,7 @@ extern void acpi_video_unregister(void);
extern int acpi_video_get_edid(struct acpi_device *device, int type,
int device_id, void **edid);
extern enum acpi_backlight_type acpi_video_get_backlight_type(void);
+extern bool acpi_video_backlight_use_native(void);
extern void acpi_video_set_dmi_backlight_type(enum acpi_backlight_type type);
/*
* Note: The value returned by acpi_video_handles_brightness_key_presses()
@@ -77,6 +78,10 @@ static inline enum acpi_backlight_type acpi_video_get_backlight_type(void)
{
return acpi_backlight_vendor;
}
+static inline bool acpi_video_backlight_use_native(void)
+{
+ return true;
+}
static inline void acpi_video_set_dmi_backlight_type(enum acpi_backlight_type type)
{
}
--
2.37.2