@@ -2182,6 +2182,30 @@ static bool dmi_is_desktop(void)
return false;
}
+/*
+ * We're seeing a lot of bogus backlight interfaces on newer machines
+ * without a LCD such as desktops, servers and HDMI sticks. Checking the
+ * lcd flag fixes this, enable this by default on any machines which are:
+ * 1. Win8 ready (where we also prefer the native backlight driver, so
+ * normally the acpi_video code should not register there anyways); *and*
+ * 2.1 Report a desktop/server DMI chassis-type, or
+ * 2.2 Are an ACPI-reduced-hardware platform (and thus won't use the EC for
+ backlight control)
+ */
+static bool should_check_lcd_flag(void)
+{
+ if (!acpi_osi_is_win8())
+ return false;
+
+ if (dmi_is_desktop())
+ return true;
+
+ if (acpi_reduced_hardware())
+ return true;
+
+ return false;
+}
+
int acpi_video_register(void)
{
int ret = 0;
@@ -2195,19 +2219,8 @@ int acpi_video_register(void)
goto leave;
}
- /*
- * We're seeing a lot of bogus backlight interfaces on newer machines
- * without a LCD such as desktops, servers and HDMI sticks. Checking
- * the lcd flag fixes this, so enable this on any machines which are
- * win8 ready (where we also prefer the native backlight driver, so
- * normally the acpi_video code should not register there anyways).
- */
- if (only_lcd == -1) {
- if (dmi_is_desktop() && acpi_osi_is_win8())
- only_lcd = true;
- else
- only_lcd = false;
- }
+ if (only_lcd == -1)
+ only_lcd = should_check_lcd_flag();
dmi_check_system(video_dmi_table);
Starting with Windows 8, Windows no longer uses the ACPI-video interface for backlight control by default. Instead backlight control is left up to the GPU drivers and these are typically directly accessing the GPU for this instead of going through ACPI. This means that the ACPI video interface is no longer being tested by many vendors, which leads to false-positive /sys/class/backlight entries on devices which don't have a backlight at all such as desktops or top-set boxes. These false-positives causes desktop environments to show a non functional brightness slider in various places. Checking the LCD flag greatly reduces the amount of false-positives, so commit 5928c281524f ("ACPI / video: Default lcd_only to true on Win8-ready and newer machines") enabled the checking of this flag by default on all win8 BIOS-es. But this let to regressions on some models, so the check was made stricter adding a DMI chassis-type check to only enable the LCD flag checking on desktop/server chassis. Unfortunately the chassis-type reported in the DMI strings is not always reliable. One class of devices where this is a problem is Intel Bay Trail-T based top-set boxes / mini PCs / HDMI sticks. These are based on reference designs which were targetets and the reference design BIOS code is often used without changing the chassis-type to something more appropriate. There are many, many Bay Trail-T based devices affected by this, so DMI quirking our way out of this is a bad idea. This patch takes a different approach, Bay Trail-T (unlike regular Bay Trail) is an ACPI-reduced-hw platform and ACPI-reduced-hw platforms generally don't have an embedded-controller and thus will use a native (GPU specific) backlight interface. This patch enables Checking the LCD flag by default on ACPI-reduced-hw platforms with a win8 BIOS independent of the reported chassis-type, fixing the false positive /sys/class/backlight entries on these devices. Note in hindsight I should have never added the DMI chassis-type check when the enabling of LCD flag checking on Windows 8 BIOS-es let to some regressions. Instead I should have added DMI quirks for the (presumably few) models where the LCD flag check let to issues. But I'm afraid that it is too late to change this now, changing this now will likely lead to a bunch of regressions. This patch was tested on a Mele PCG03 mini PC. Signed-off-by: Hans de Goede <hdegoede@redhat.com> --- drivers/acpi/acpi_video.c | 39 ++++++++++++++++++++++++++------------- 1 file changed, 26 insertions(+), 13 deletions(-)