On 03/18/2013 05:25 PM, Seth Forshee wrote: > On Thu, Mar 07, 2013 at 01:38:12PM -0600, Seth Forshee wrote: >> On Wed, Feb 13, 2013 at 08:55:58PM +0000, Matthew Garrett wrote: >>> On Wed, Feb 13, 2013 at 02:32:28PM -0600, Seth Forshee wrote: >>>> On Mon, Feb 11, 2013 at 07:09:14PM +0000, Matthew Garrett wrote: >>>>> Right. My concern here is that Windows clearly doesn't trigger the >>>>> issue, and so there's some chance that we'll see similar issues on other >>>>> machines. Disabling Windows 8 compatibility isn't really an option. One >>>>> choice might be to have the ACPI video driver set all intermediate >>>>> values if the system makes the Windows 8 OSI call? >>>> >>>> This turns out to have some problems. The hotkeys on the x230 at least >>>> generate increase/decrease brightness notifications. In response >>>> acpi_video reads the current brightness level via _BQC and decides what >>>> the next value should be. A value adjacent to a working value is never >>>> another working value on this machine, so _BCM does nothing. The next >>>> time a notification comes _BQC returns the same value as it did the >>>> previous time. Obviously this gets us nowhere. >>> >>> Nrgh. Having this logic in the kernel has always been miserable. On the >>> other hand, having _BQC return wrong values is arguably even worse. >>> >>>> The (untested) fix I've come up with is to use the cached value for the >>>> current brightness rather than asking the firmware. I'm assuming though >>>> that acpi_video would be using the cached values already if there wasn't >>>> a chance that their changing without its knowledge? >>> >>> Yeah. What I'd suggest here is calling _BQC after every change, and if >>> it returns the old value throw a firmware bug message and fall back to >>> using a cached one. >>> >>>> The other issue with using the cached value is that the hotkeys on these >>>> machines are still going to end up cycling through 101 brightness levels >>>> with 85% of them leaving the brightness unchanged. When there's that >>>> many levels though maybe it makes sense to jump more than one level at a >>>> time. >>> >>> Right. I'd recommend turning off that functionality and just leaving it >>> up to userspace. We still seem to be carrying a patch to do that in >>> Fedora. I thought I had a patch to make this a config option somewhere, >>> but can't find any sign of it now... >> >> I've had the patches implementing your suggestions written for a while >> now but just got test feedback this week. So here they are. > > Ping. > > Matthew, do these patches look like what you had in mind? Finally got a chance to try these patches out. It seems to perform as expected, exposing levels 0-100 and actually allowing proper changes between them. It's not optimal, though. Using the up/down keys with gnome-settings-daemon, which uses 20 steps, several steps don't actually change the brightness (including the very first one, 100->95). Additionally, the changes are asymmetric: going down, the brightness changes at 95->90, but going up 90->95 has no change, and 95->100 changes it. As a user, I'd definitely consider this a regression compared to the "!Windows 2012" behavior. If you can't remove that OSI or override the _BCL list as a machine-specific quirk, this is probably the best generic behavior possible, though. -Ben -- 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
