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. Thanks, Aaron > + if (state == curr_state) > + offset = 0; > + else > + offset = state > curr_state ? 1 : -1; > + } else { > + offset = state - curr_state; > } > > - device->brightness->curr_state = state; > + do { > + curr_state += offset; > + arg0.integer.value = device->brightness->levels[curr_state]; > + > + status = acpi_evaluate_object(device->dev->handle, "_BCM", > + &args, NULL); > + if (ACPI_FAILURE(status)) { > + ACPI_ERROR((AE_INFO, "Evaluating _BCM failed")); > + > + /* > + * Change curr_state back to that of last > + * successful _BCM call > + */ > + curr_state -= offset; > + result = -EIO; > + break; > + } > + } while (curr_state != state); > + > + device->brightness->curr_state = curr_state; > if (device->backlight) > - device->backlight->props.brightness = state - 2; > + device->backlight->props.brightness = curr_state - 2; > > - return 0; > + return result; > } > > static int > -- 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
