On Tuesday, July 30, 2013 01:57:55 PM Aaron Lu wrote: > On 07/30/2013 01:51 PM, Aaron Lu wrote: > > On 07/30/2013 11:44 AM, Felipe Contreras wrote: > >> On Mon, Jul 29, 2013 at 10:11 PM, Aaron Lu <aaron.lwe@xxxxxxxxx> wrote: > >>> On 07/30/2013 03:20 AM, Felipe Contreras wrote: > >>>> Since v3.7 the acpi backlight driver doesn't work at all on this machine > >>>> because presumably the ACPI code contains stub code when Windows 8 OSI is > >>>> reported. > >>>> > >>>> The commit ea45ea7 (in v3.11-rc2) tried to fix this problem by using the intel > >>>> backlight driver, however, on this machine it turns the backlight completely > >>>> off when it reaches level 0%, after which the user might have a lot trouble > >>>> trying to bring it back. > >>> > >>> What do you mean by a lot of trouble? If you press hotkey to increase > >>> backlight brightness level, does it work? > >> > >> I guess so, *if* there is indeed a user-space power manager handling > >> that, *and* the keyboard has such keys, *or* the user has set custom > >> hotkeys. > > > > Right, for a GUI environment this may not be a big problem(user uses Fn > > key to decrease brightness level and then hit the black screen, it's > > natural he will use Fn key to increase brightness level). > > > >> > >>> If so, the screen should not > >>> be black any more, it's not that user has to blindly enter some command > >>> to get out of the black screen. > >>> > >>> And I'm not sure if this is a bug of intel_backlight(setting a low level > >>> makes the screen almost off), I see different models with different > >>> vendors having this behavior. > >> > >> I mean, the screen is completely off, I cannot see absolutely > >> anything. I don't see this behavior with the ACPI backlight driver, > >> nor do I see that in Windows 7. > >> > >>> If this is deemed a bug, then I'm afraid > >>> intel_backlight interface is useless for a lot of systems...perhaps we > >>> can only say, intel_backlight's interpretation of low levels are > >>> different with ACPI video's, and that's probably why its type is named > >>> as raw :-) > >> > >> Well, a bug is defined as unexpected behavior -- as a user, if I'm > >> changing the brightness of the screen, I certainly don't expect the > >> screen to turn off, and I think that's the expectation from most > >> people. It's the first time I see something like that. > > > > I agree this is kind of un-expected. At the same time, this seems to be > > the normal behavior for intel_backlight. I don't know what the correct > > thing to do here if this is something we want to avoid - modify intel > > backlight handling code not to set too low value or change the user > > space tool not to set a too low value if they are interacting with a > > raw type interface. Neither of them sounds cool... Or, users may get > > used to it, I for example, don't find this to be very annoying, but > > maybe I'm already used to it. > > BTW, for the complete screen off problem, I don't see there is anything > wrong with it from code's point of view. It's not that there is an error > in code or this is a broken hardware that caused the screen off when > setting a very low or 0 brightness level, it is simply the expected > behavior of what this interface can provide. It can really set the > brightness level to minimum(zero) or maximum. Don't get me wrong, I > didn't mean this is a good user experience, I don't know that. I just > don't think this is a program bug, and I don't know if this should be > fixed or not - obviously this interface did what it is asked to do, > correctly. Precisely, user space asks for 0 and the kernel delivers. And there are reasons why 0 should be "screen off", like power management (when you have a policy to dim the screen completely after a period of inactivity, for example). So in my opinion, if that's a problem for anyone, it has to be addressed in user space and if there are any vendors who try to address *that* in their ACPI tables, that's one more reason to avoid using ACPI for backlight control. Thanks, Rafael -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center. -- 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
