On Sun, Mar 31, 2013 at 09:04:21AM +0200, Danny Baumann wrote: > Hi, > > Artem Savkov <artem.savkov@xxxxxxxxx> schrieb: > > >On Sun, Mar 31, 2013 at 08:15:14AM +0200, Danny Baumann wrote: > >> Artem Savkov <artem.savkov@xxxxxxxxx> schrieb: > >> >acpi_video_device_lcd_get_level_current() called > >> >acpi_video_bqc_value_to_level() > >> >with "*level" as a second argument, resulting in level being > >returned > >> >based on > >> >initial input, not current brightness, breaking backlight controls. > >> I don't think this change is correct. As level was passed as > >parameter into the evaluation of _BQC, *level contains the AML returned > >brightness level afterwards, so it's correct to use it as an input to > >acpi_video_bqc_value_to_level(). Actually, the whole point of > >acpi_video_device_lcd_get_level_current() is to update > >device->brightness->curr, so it doesn't make sense to me to use it in > >that function. > >> > >> What's the exact problem this patch tries to solve? > > > >I'm running a -next kernel on my laptop and couple of days ago keyboard > >backlight controls stopped working: only 2 lower brightness levels. > >I've > >debugged it a bit and found out that acpi_video_switch_brightness() > >calls > >acpi_video_device_lcd_get_level_current() with level uninitialized and > >always gets lowest posible value. > > The point is: after the acpi_evaluate_object call, *level must contain the current brightness level, otherwise your BIOS is broken (this happens: e.g. my laptop always returns 100 from _BQC in Windows 8 mode). You can verify this easily by initializing level_current to some invalid value and checking it again after the call to _get_level_current. I'd be pretty surprised if the value didn't change. Also, if you look at [1], you'll see that the code operated on *level before as well. > This problem may have been obscured by the fact that the brightness device wasn't initialized properly before my patches went in. Does acpi_video_switch_brightness actually do anything for you when reverting the 3 newest commits of video.c? Yes, you are right. Both my patch and the version before your patches result in initial acpi_video_device_lcd_get_level_current call ending with invalid level being returned and bqc disabled, so they both just use *level = brightness->curr after that. -- Regards, Artem -- 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
