On 07/31/2013 04:59 AM, Felipe Contreras wrote: > 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. I'm not sure of this. Remember the days when we switch the hard disk driver from IDE to SCSI? The block device name changed from hdx to sdx. Is this 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*. That depends on how you see it. I believe 0 also turns off the screen in v3.10 if we are talking about the same driver(intel_backlight). -Aaron > >> 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 > -- 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
