On Wednesday 24 September 2014 10:19:38 Hans de Goede wrote: > Hi, > > On 09/23/2014 10:44 PM, Pali Rohár wrote: > > On Tuesday 23 September 2014 22:31:31 you wrote: > >> Hi, > >> > >> On 09/23/2014 10:06 PM, Pali Rohár wrote: > >>> Hello, > >>> > >>> after big changes in acpi video/i915 code I cannot change > >>> display brightness on my Dell Latitude E6440 with kernel > >>> 3.17-rc6. With kernel 3.13 everything worked fine. > >>> > >>> More information about this problem: > >>> > >>> For configuring brightness on Dell laptops there are 4 > >>> ways: 1) via acpi video driver > >>> 2) via dell-laptop driver > >>> 3) via i915 drm driver > >>> 4) from userspace with special dell SMI call > >>> > >>> (e.g with program dellLcdBrightness from libsmbios > >>> package) > >>> > >>> Methods 2) and 4) are same, both making special SMI call > >>> and Bios handing this request (just 2 is from kernel and > >>> 4 from userspace) > >>> > >>> Method 1) via acpi video driver working, but is not > >>> perfect. Driver can be used to change brightness (but > >>> only some levels, probably this depends on acpi/DSDT > >>> tables), but cannot be used to retrieve current > >>> brightness (when BIOS/SMI change brightness acpi driver > >>> report old incorrect value). So I prefer dell-laptop > >>> driver instead acpi video. > >>> > >>> Method 3) working even with 3.17-rc6 kernel but because > >>> that backlight device exported by i915 is marked as raw, > >>> desktop programs prefer to use other devices. > >>> > >>> Moreover it looks like that methods 1) 2) and 4) just > >>> forward request to method 3). So in any cased brightness > >>> is changed by i915 drm driver. > >>> > >>> I'm not sure (correct me if I'm wrong!) but I think that > >>> intel i915 drm driver accept changes (file > >>> intel_opregion.c) only if acpi function > >>> acpi_video_verify_backlight_support() returns true. > >>> > >>> Function acpi_video_verify_backlight_support() returns > >>> true iff: function acpi_video_backlight_support() returns > >>> true AND at least one of these functions returns false: > >>> acpi_osi_is_win8() > >>> acpi_video_use_native_backlight() > >>> backlight_device_registered(BACKLIGHT_RAW) > >>> > >>> On my notebook acpi_osi_is_win8() returns true (as is win8 > >>> compliant), backlight_device_registered(BACKLIGHT_RAW) > >>> returns true as I'm using intel i915 drm driver with raw > >>> backlight device and acpi_video_use_native_backlight() > >>> returns true/false depending on > >>> "video.use_native_backlight" kernel param. Default is > >>> true. > >>> > >>> So if I want to have working acpi video driver with > >>> display brightness support I need to boot kernel with > >>> param: "video.use_native_backlight=0". I tested it with > >>> kernel 3.17-rc6 and this param really enabled display > >>> brightness support via acpi video driver -- which is > >>> good. > >>> > >>> Driver dell-laptop creating backligh device for brightness > >>> control only if acpi_video_backlight_support() returns > >>> false. There is complicated condition for it and when > >>> kernel is booted with "video.use_native_backlight=0" that > >>> function returns true. > >>> > >>> So conclusion is: With current code in kernel 3.17-rc6 it > >>> is not possible to control brightness of display with > >>> native driver dell-laptop on Dell Latitude E6440 (and > >>> probably on others too)!!! > >>> > >>> And Because laptop is win8 compliant and you create > >>> decision to use native driver (instead acpi one) it is > >>> not possible to control display brightness without tweeks > >>> in kernel cmdline. > >>> > >>> As I wrote I would rather to use native dell-laptop driver > >>> for controlling brightness, but it is not possible. > >>> > >>> So how to solve this problem? > >>> > >>> Quick solution would be to set use_native_backlight false > >>> for some Dell laptops which means, that acpi video will be > >>> used and in this case intel i915 driver will *not* drop > >>> backlight change request. > >>> > >>> Another solution could be to disable check in dell_laptop > >>> driver and add use_native_backlight=0 to hooks. But this > >>> create two backlight interfaces (which is not good), but > >>> only way (for now) how to make dell_laptop working again. > >>> > >>> Better and maybe only one proper solution would be to > >>> teach intel drm i915 driver to not drop backlight change > >>> request for Dell laptops (or all??). (This allows to work > >>> both acpi video and dell_laptop drivers without any > >>> change and with *any* value in param > >>> use_native_backlight). I think that problematic code is > >>> in function asle_set_backlight() in file intel_opregion.c > >>> (but I'm not sure). My idea is that "drop" event function > >>> it is caused by this commit > >>> 0b9f7d93ca6109048a4eb06332b666b6e29df4fe (but I'm not > >>> sure). > >>> > >>> At least something must be done as I think that I'm not > >>> only one who has Dell laptop and brightness configuration > >>> is really important... > >> > >> I don't understand your problem, the kernel is selecting > >> the i915 backlight driver, making that the only one > >> available to userspace, so the one problem you state with > >> the i915 driver, that it is "raw" is not an issue, as > >> userspace will pick it when it is the only one. > > > > It is not only one. > > Are you sure, if you do not specify any commandline > parameters, then neither dell-laptop nor acpi-video should > register a backlight interface. > > dell-laptop.c has: > > #ifdef CONFIG_ACPI > /* In the event of an ACPI backlight being available, > don't * register the platform controller. > */ > if (acpi_video_backlight_support()) > return 0; > #endif > > And acpi_video_backlight_support() will (normally) return true > on acpi-backlight capable systems independent of > use_native_backlight. > > And drivers/acpi/video.c has this: > > /* no warning message if acpi_backlight=vendor or a > quirk is used */ if (!acpi_video_verify_backlight_support()) > return; > > ... > > bool acpi_video_verify_backlight_support(void) > { > if (acpi_osi_is_win8() && > acpi_video_use_native_backlight() && > backlight_device_registered(BACKLIGHT_RAW)) return false; > return acpi_video_backlight_support(); > } > > So unlike the check in dell-laptop this one does depend on the > use_native_backlight setting. > It depends (see my previous mail). Here is code: static bool acpi_video_use_native_backlight(void) { if (use_native_backlight_param != -1) return use_native_backlight_param; else return use_native_backlight_dmi; } > I've just checked 3.17 on my E6430 and there this works as it > should, I only get the intel_backlight in > /sys/class/backlight > > > Also dell-laptop (or acpi video) backlight > > interface is created (depends on use_native_backlight > > param). And userspace will pick dell-laptop (or acpi video) > > to use (which cannot change brightness). > > > >> Why would you want to use dell-laptop despite the i915 > >> driver working fine ? > > > > i915 working only if I compile kernel without acpi video > > dell- laptop support (distributions compile kernel with > > these drivers) and i915 is not good for usage. First it > > provides more then thousand brightness levels and lot of > > (with low numbers) completely turn display off. And if > > userspace map these thousand levels into 5-10 levels (as > > nobody want to press brightness key up/down 1000x) two > > lowest levels cause display off. > > More and more laptops will only have working backlight control > at all when using i915, so userspace will need to learn to > better deal with backlight controls with these ranges. And > low pwm levels turning the backlight of is normal for raw > interfaces, if userspace does not want this, then they should > not go so low. > So then kernel should report which low levels turn backlight off so userspace will know which levels should avoid. But this is not implemented yet. > I suggest that you file a bug against your desktop environment > that it is not using the backlight controls in an optimal > manner, from the kernel pov everything is working fine. > Once I will know which levels should not DE use I can report bug. > > With acpi > > video and dell-laptop driver levels are mapped into small > > level space in perfect way. So this is reason I want to use > > dell-laptop for controlling brightness. > > If you want to use dell-laptop, specify acpi_backlight=vendor > on the kernel commandline, that will give you dell_laptop + > intel_backlight as backlight interfaces, and userspace should > prefer dell_laptop. With acpi_backlight=vendor dell-laptop is not working, see my previous mail. In this case intel i915 drm driver ignore bios events for changing brightness. And userspace prefer to use dell_laptop which do nothing! > But IMHO it would be better to file a bug > with your desktop environment, and get that fixed to work > properly with intel_backlight (or with raw backlight > interfaces in general). > > Regards, > > Hans > > >> Regards, > >> > >> Hans -- Pali Rohár pali.rohar@xxxxxxxxx
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