On Tue, Jul 30, 2013 at 6:13 PM, Rafael J. Wysocki <rjw@xxxxxxx> wrote: >> 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. > > The ACPI driver simply exposes and interface to interact with the AML methods > in the BIOS directly. No, the ACPI driver is exposing a backlight interface, which has a defined stable API. Documentation/ABI/stable/sysfs-class-backlight Yes, the interface doesn't define what should happen at 0, that is a bug in the interface definition. *How* it achieves that is an implementation detail. > Yes, this is a mistake and shouldn't be designed this way. > > However, incidentally, this makes backlight control work on your machine. > > Anyway, we need all backlight drivers to work consistently and don't tempt me > to rip the ACPI driver entirely from the kernel for what it's worth. Yes, they should work consistently, and go ahead, rip the ACPI driver, *then* you'll see many more people complaining about the Linux kernel breaking user-space, which should never happen. Mistakes happen, but if you do this willingly and knowingly, I think there would be repercussions for you. > Yes, that will break backlight on your system and *then* you can complain to > Linus if you wish. It is already broken in v3.11-rc3, in fact I just booted that to try it out and it booted with the screen completely black (fortunately I knew exactly what to type to change that). Apparently this commit also needs to be reverted: efaa14c (ACPI / video: no automatic brightness changes by win8-compatible firmware). In this machine it makes the backlight work again (without acpi_osi="!Windows 2012"), but by doing so the ACPI driver also turns off the screen completely at level 0. Also, each time I change the backlight level from X, the screen blinks as if going 100%, 0%, and then the desired level. For this particular machine simply applying the attached patch would solve all those regressions, but who knows in other machines, I think it's safer to revert efaa14c. -- 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
