Re: ACPI/i915: Cannot configure display brightness on Dell Latitude E6440

Pali Rohár
2014-09-24T12:53:46Z

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On Wednesday 24 September 2014 14:04:36 Hans de Goede wrote:
> Hi,
>
> On 09/24/2014 11:14 AM, Pali Rohár wrote:
> > On Wednesday 24 September 2014 10:59:41 Pali Rohár wrote:
> >> 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;
> >>
> >> }
>
> Not sure what you're trying to say here, the default for
> this is 1, so if you don't specify anything, then this:
>
> 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();
> }
>
> Will return false, and you won't get an acpi_video0 backlight
> interface, only the intel_backlight one, and everything
> should just work (except for the turning off on low
> settings).
>

When I do not specify param acpi_video_verify_backlight_support()
will return false because acpi_osi_is_win8() returns true.

> Have you tried not using any kernel commandline options? What
> happens?
>

Yes, then kernel create two backlight devices: one raw from i915
module and one normal from dell-laptop module. Userspace will
pick dell-laptop for using. And due to commit 0b9f7d93 (which
disabling events when acpi_video_verify_backlight_support returns
false) dell-laptop backlight not working. So controlling
brightness from userspace does not work.

> >>> 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!
> >
> > Ok, that problematic commit is:
> >
> > ACPI / i915: ignore firmware requests for backlight change
> > 0b9f7d93ca6109048a4eb06332b666b6e29df4fe
> >
> > When I reverted it acpi_backlight=vendor started working
> > again (via dell_laptop). Without reverting that commit
> > dell_laptop simply do nothing.
> >
> > Tested and on my laptop Dell Latitude E6440 driver
> > dell_laptop does not work with above commit.
>
> Hmm, interesting, so when dell-laptop registers and makes a
> few calls using the dell-laptop acpi interface,

No, dell-laptop is *not* acpi driver. See my first mail. It uses
dell dcdbas driver which makes SMI calls for SMBIOS. But it (on
my machine! no idea about other older once) just forward
brightness change to intel driver. And it has useful brightness
levels (no lot of levels which turning display off).

And making SMI calls can be done also from userspace. There is
tool dellLcdBrightness in libsmbios package which for brightness.
And commit 0b9f7d93ca6109048a4eb06332b666b6e29df4fe broke
functionality of that tool.

> then you either stop getting key press events through the
> acpi-video-bus, or dell-laptop is just a shim around the i915
> interface with the firmware calling into itself on these
> models. Given that dell-laptop is ancient, the shim story is
> not that far fetched.
>

Brightness Fn keys are reported by WMI (dell-wmi driver), so they
working without dell-laptop and acpi video drivers perfectly.

> Do you still get an on screen display showing the brightness
> when using a kernel without this patch +
> acpi_backlight=vendor ?
>

Brightness Fn keys are reported to userspace (from WMI input
device) with any combination of video.use_native_backlight and
acpi_backlight kernel params.

> Regards,
>
> Hans

--
Pali Rohár
pali.rohar@gmail.com

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