Hi On Sat, Jan 17, 2015 at 1:32 PM, Topi Miettinen <toiwo...@gmail.com> wrote: > On 01/17/15 12:19, David Herrmann wrote: >> Hi >> >> On Sat, Jan 17, 2015 at 1:10 PM, Topi Miettinen <toiwo...@gmail.com> wrote: >>> On 01/17/15 12:03, David Herrmann wrote: >>>> Hi >>>> >>>> On Sat, Jan 17, 2015 at 1:01 PM, Topi Miettinen <toiwo...@gmail.com> wrote: >>>>> On 01/17/15 11:38, David Herrmann wrote: >>>>>> Hi >>>>>> >>>>>> On Sat, Jan 17, 2015 at 12:28 PM, Topi Miettinen <toiwo...@gmail.com> >>>>>> wrote: >>>>>>> On my computer, the minimum brightness enforced by clamping in >>>>>>> backlight is too bright. >>>>>> >>>>>> How can 5% of the backlight be "too bright"? Can you give some >>>>>> information on your backlight device? (type, max_brightness, >>>>>> actual_brightness and so on). >>>>> >>>>> Well, my eyes start to hurt with level 1, 0 is OK. Max_brightness is 9, >>>>> actual_brightness always matches brightness. This is cheap old Acer >>>>> Aspire 8530 laptop with Mobility Radeon HD 3200, I don't know beyond >>>>> that what handles backlight. >>>> >>>> Which backlight driver is active? acpi? Or the native radeon driver? >>> >>> The device path is >>> /sys/devices/pci0000\:00/0000\:00\:01.0/0000\:01\:05.0/backlight/acpi_video0/brightness, >>> does that mean acpi? >> >> The problem here is, there're 2 types of backlight drivers in the kernel: >> >> 1) backlight==0 is interpreted as 'off' >> 2) backlight==0 is interpreted as 'lowest level that is not "off"' >> >> There is a second switch called 'bl_power' which allows to actually >> power the backlight off or on. This works on all devices the same way. >> However, if we want to figure out the lowest backlight level, we >> really cannot use '0' as we have no idea how the driver will interpret >> it. > > I see. Here, setting bl_power to 0 does nothing,
Sure, if the hardware does not support power-down, it will not work. >> >> We discussed this at the last XDC but haven't really come to a >> conclusion. This is definitely a kernel bug, as user-space has no >> chance of setting a backlight generically to "lowest level". If there >> were a property called "min_brightness" that exposes the minimal >> brightness level supported (which is not 'off'), we could parse it. >> However, we don't want to write per-driver workarounds in userspace if >> kernel people could just fix it. >> >> Conclusion: Lets try getting kernel backlight people to solve this mess. > > That may be the proper long term path, but because there's already a > clamping workaround which does not do the right thing for all hardware, > this override would be useful for such cases until the kernel is fixed. > After the kernel is fixed, the clamping (along this override) should not > be applied anymore. No, we still need clamping! In case your hardware has 256 brightness levels, we really don't want a brightness of 1 as it would still be far too dark. Thanks David _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
