Hi Hans,
Thank you for warning about the potential regressions that could happen due to the backlight changes in the Linux kernel.
Sorry if this reply sounds a bit scatterbrained, it is very late.
On Tue, Nov 1, 2022 at 7:11 PM Hans de Goede hdegoede@redhat.com wrote:
Just wondering. I'm happy to see coreboot adjusted to make the kernels heuristics work. OTOH though coreboot BIOS users really should not need to upgrade their BIOS to stop things breaking with a new kernel.
I'm not entirely sure what the right balance is.
It is true that firmware updates are risky, and that having to deal with things breaking after an OS update is unpleasant. However, one of the good things about coreboot is that firmware bugs can be fixed (at least most of them). Maximizing compatibility is important, but so is getting firmware bugs fixed. Maybe the right balance is to work around coreboot bugs in the kernel (if necessary) in a way that allows them to be fixed in coreboot, and of course communicate with coreboot (this email is a good example). One of the worst things that could happen is for coreboot to have to work around OSes' workarounds for coreboot because coreboot was broken and the OSes' workarounds are too inflexible for coreboot to start doing the right things: effectively, it would be a deadlock.
Note that I plan to submit a revert for the patch which hides: /sys/class/backlight/intel_backlight when the acpi_video_get_backlight_type() heuristics say that another backlight interface should be used, since it seems that this will break quite a few (mostly older, beginning of Intel x86_64 era) laptops.
Do you have any examples? coreboot supports several older Intel x86_64 platforms, including laptops, that could be affected too.
So with the final 6.1 /sys/class/backlight/intel_backlight should stay around, but I do want to try again later since I really want to get rid of the having multiple /sys/class/backlight/ entries for a single panel and then let userspace choose shenanigans.
Agreed. Having multiple backlight entries is confusing, especially when using the same OS install on a bunch of different machines.
I've some ideas on how to change the heuristics which will hopefully fix the beginning of Intel x86_64 era laptops, but I don't think those will help on the coreboot using System76 laptops case...
Well, there's a firmware bug anyway, because brightness controls don't work on Alder Lake when using Windows. And it doesn't look like Windows will accept pull requests anytime soon...
An idea (which may be impractical to implement) would be to not expose intel_backlight if ACPI backlight control is available.
Regards,
Hans
Best regards,
Angel