On Tue, Jul 30, 2013 at 8:42 AM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: > 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). There is another interface the turn the screen off. If 0 turns the screen off with the intel driver, 0 should turn the screen off with the ACPI driver, having inconsistent behavior depending on which driver is used is a bug. If 0 did not turn off the screen in v3.10, 0 should not turn off the screen in v3.11, to do so would be a *regression*. > 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. If you think it's the user-space responsibility to deal with kernel bugs, I think it's only a matter of time before you receive one of these [1]. "If a change results in user programs breaking, it's a bug in the kernel. We never EVER blame the user programs. How hard can this be to understand?" "WE DO NOT BREAK USERSPACE!" [1] https://lkml.org/lkml/2012/12/23/75 -- Felipe Contreras -- 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
