On Fri, Oct 11, 2013 at 4:27 PM, Rafael J. Wysocki rjw@rjwysocki.net wrote:
On Friday, October 11, 2013 06:01:43 PM Josh Boyer wrote:
On Fri, Oct 11, 2013 at 6:10 PM, Rafael J. Wysocki rjw@rjwysocki.net wrote:
On Friday, October 11, 2013 12:42:43 PM Josh Boyer wrote:
On Fri, Oct 11, 2013 at 9:27 AM, Aaron Lu aaron.lu@intel.com wrote:
v5: 1 Introduce video.use_native_backlight module parameter and set its value to false by default as suggested by Rafael. For Win8 systems which have broken ACPI video backlight control, the parameter can be set to 1 in kernel cmdline to skip registering ACPI video's backlight interface. Due to this change, the acpi_video_verify_backlight_support is moved from video_detect.c to video.c - patch 3/4;
That's a fairly untenable position for distro kernels to be in. They now have to ask every user that reports an issue with the backlight to try setting that option on the command line. While I appreciate the setting breaks things for some people, doesn't the Win8 issue impact far more people? Shouldn't it be defaulted to true?
Well, we have a rule in the kernel not to introduce regressions for users even if they are minority.
If nothing else, can you add a config option for the default so distros can use that to decide which way to default it and then work on fixing the remaining users that have troubles?
The current plan is to create a blacklist of systems where that option should be set. We actually already have one, but it is at the _OSI() level, which is overkill in my view and may affect things beyond backlight. Along with that we will debug systems where setting that option (to true) causes problems to happen, so that we'll be able to drop it going forward (hopefully).
Of course, distro kernels may always change the default to true if they want.
They can, but they'd need to either patch the kernel to do so, or code it in userspace bootloader configs. Having a config option they can set to change the default makes it reasonable and contained within the kernel.
If we are to use a Kconfig option, why don't we use one instead of rather than in addition to a command line option? Say, we have CONFIG_ACPI_VIDEO_WIN8_WORKAROUND and if that is set, the code will work like the previous version of the Aaron's patchset (the one without video.use_native_backlight)?
Opinions?
If you only have a config option, users can't override the distro settings. If you simply have a config option for the default value, the distros can set it without having to carry a patch (the primary benefit), but users can still override that without having to rebuild a kernel.
josh