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

Pali Rohár
2014-09-24T18:21:10Z

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On Wednesday 24 September 2014 16:34:21 Hans de Goede wrote:
> Hi,
>
> On 09/24/2014 02:53 PM, Pali Rohár wrote:
> > 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.
>
> Erm, no it won't, unless you've other kernel commandline
> options active as well. dell-laptop contains this:
>
> #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 still report 1, so
> dell-laptop will not register a backlight interface unless
> your meddling with things / config options.
>

Right, sorry for this. Without *any* kernel cmdline only intel
backlight is registered and userspace will pick up it.

> > 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.
>
> Right, so stop doing whatever you are doing which causes
> dell-laptop to register a backlight interface as by default
> it will not do that, and your problem is gone.
>
> >>>>> 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.
>
> Ok, so the dell-laptop interface is just an obsolete wrapper
> around the i915 opregion code, which shows that the right
> interface to use is the i915 one, which we do if you don't
> specify any kernel commandline parameters, case closed.
>
> Regards,
>
> Hans

Nope, its not closed.

Still i915 interface has problem with setting backlight. It
exports lot of levels which turning display off. Which breaking
exiting applications for configuring display brightness. This is
still big regression as black screen is not want people want to
see.

Driver dell-laptop has exported only few - not thousands level
(which is insane) and only usefull levels (not lot of levels
which turn display off).

So for this reason using i915 backlight interface is not possible
and also Dell (for E6440) set kernel param acpi_backlight=vendor
to use dell_laptop module for controlling brightness.

On my laptop E6440 is better for using dell-laptop and not acpi
or i915.

--
Pali Rohár
pali.rohar@gmail.com

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