On 04/04/2013 08:35 PM, Seth Forshee wrote: > On Thu, Apr 04, 2013 at 07:44:04PM +0800, Aaron Lu wrote: >> On 03/08/2013 03:39 AM, Seth Forshee wrote: >>> Windows 8 requires that all backlights report 101 brightness levels. >>> When Lenovo updated the firmware for some machines for Windows 8 they >>> met this requirement my making _BCL return a larger set of values for >>> Windows 8 than for other OSes. However, only the values in the smaller >>> set actually change the brightness at all. The rest of the values are >>> silently discarded. >>> >>> As a workaround, change acpi_video to set all intermediate backlight >>> levels when setting the brightness. This isn't perfect, but it will mean >>> that most brightness changes done by common userspace utilities will hit >>> at least one valid brightness value. >>> >>> [1] http://msdn.microsoft.com/en-us/library/windows/hardware/jj128256.aspx >>> >>> Signed-off-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx> >>> --- >>> drivers/acpi/video.c | 51 ++++++++++++++++++++++++++++++++++++++++---------- >>> 1 file changed, 41 insertions(+), 10 deletions(-) >>> >>> diff --git a/drivers/acpi/video.c b/drivers/acpi/video.c >>> index edfcd74..b83fbbd 100644 >>> --- a/drivers/acpi/video.c >>> +++ b/drivers/acpi/video.c >>> @@ -352,25 +352,56 @@ acpi_video_device_lcd_query_levels(struct acpi_video_device *device, >>> static int >>> acpi_video_device_lcd_set_state(struct acpi_video_device *device, int state) >>> { >>> - int level = device->brightness->levels[state]; >>> union acpi_object arg0 = { ACPI_TYPE_INTEGER }; >>> struct acpi_object_list args = { 1, &arg0 }; >>> + int curr_state, offset; >>> acpi_status status; >>> + int result = 0; >>> >>> - arg0.integer.value = level; >>> + curr_state = device->brightness->curr_state; >>> >>> - status = acpi_evaluate_object(device->dev->handle, "_BCM", >>> - &args, NULL); >>> - if (ACPI_FAILURE(status)) { >>> - ACPI_ERROR((AE_INFO, "Evaluating _BCM failed")); >>> - return -EIO; >>> + /* >>> + * Some Lenovo firmware has a broken backlight implementation >>> + * for Windows 8 where _BCL returns 101 backlight levels but >>> + * only 16 or so levels actually change the brightness at all. >>> + * As a workaround for these machines we set every intermediate >>> + * value between the old and new brightness levels whenever the >>> + * system has made the Windows 8 OSI call, hoping that at least >>> + * one of them will cause a change in brightness. >>> + */ >>> + if (acpi_osi_windows_version() == ACPI_OSI_WIN_8) { >> >> What do you think of testing br->count > 100 instead of OSI version? It >> looks like only win8 systems will try to claim so many brightness levels. > > I agree that it would be roughly the same set of machines today. But if > we assume Microsoft will keep the same requirement in the future then it > begins to expand beyond Windows 8. Right, and the br->count > 100 test should also work, so it seems to be a better condition check than OSI version. > > If anything I'd prefer reducing the number of machines we apply this > workaround to. Like say limiting it to Lenovo Win8 machines, if we can > reasonably assume that Lenovo will be the only vendor with this > ridiculous implementation. This is probably not the case. I saw a Dell system also claims to have 100 levels in win8 mode: https://bugzilla.kernel.org/show_bug.cgi?id=55071 Thanks, Aaron -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
