backlight not adjustable after screen turns off and then back on

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This change was made by a bot.

I've tested with the latest upstream kernel.

test@test-Dell-System-XPS-L322X:~$ uname -a
Linux test-Dell-System-XPS-L322X 3.9.0-030900rc4-generic #201303232035 SMP Sun Mar 24 00:36:21 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

This issue appears to be an upstream bug, since you tested the latest upstream kernel. Would it be possible for you to open an upstream bug report[0]? That will allow the upstream Developers to examine the issue, and may provide a quicker resolution to the bug.

Please follow the instructions on the wiki page[0]. The first step is to email the appropriate mailing list. If no response is received, then a bug may be opened on bugzilla.kernel.org.

[0] https://wiki.ubuntu.com/Bugs/Upstream/kernel

Also, was there a prior kernel version that did not exhibit this bug?

Yes, Ubuntu 12.04 does not have this issue.

Actually, I see that 3.9-rc5 was released yesterday, and it contains this change:
Revert "drm/i915: write backlight harder"
http://permalink.gmane.org/gmane.linux.kernel.commits.head/372554

Right now, someone else is using the L322X I was testing with, so I can't check rc5 at the moment.

It would be great if you could test rc5[0] and post the results.

Thanks in advance!

[0] http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.9-rc5-raring/

If the bug still exists in 3.9-rc5, we can perform a bisect to identify the commit that introduced this regression.

@jsalisbury, I think I know the code that's causing the trouble, and will look into the issue here; no bisect is necessary.

Tested the kernel in raring-proposed today and things are much better. After letting the screen turn off and then back on I no longer lose the ability to adjust screen brightness. I can still adjust screen brightness after suspend / resume, too. This is on an L322X.

Thanks for the confirmation, Kent.

This problem is fixed (for the old and new Dell XPS 13 models) in the next Raring kernel (3.8.0-18.28), which is available now in raring-proposed (see https://wiki.ubuntu.com/Testing/EnableProposed ).

This bug was fixed in the package linux - 3.8.0-18.28

---------------
linux (3.8.0-18.28) raring; urgency=low

  [ Andy Whitcroft ]

  * (debian) fix internal linkage for separated header packages
    - LP: #1165259

  [ Gavin Guo ]

  * SAUCE: Bluetooth: Add support for Broadcom 413c:8143
    - LP: #1166113

  [ John Johansen ]

  * SAUCE: (no-up) apparmor: Fix quieting of audit messages for network
    mediation
    - LP: #1163259

  [ Kamal Mostafa ]

  * SAUCE: (no-up) drm/i915: quirk no PCH_PWM_ENABLE for Dell XPS13
    backlight
    - LP: #1162026, #1163720

  [ Leann Ogasawara ]

  * [Config] Disable CONFIG_PARPORT_PC_FIFO
    - LP: #339752

  [ Martin Pitt ]

  * SAUCE: (no-up) mac80211_hwsim: Register and bind to driver
    - LP: #1166250

  [ Paolo Pisati ]

  * [Config] RTC_DRV_PL031=y

  [ Stefan Bader ]

  * (debian) Abort build on unresolved symbols
    - LP: #1166197

  [ Tim Gardner ]

  * [Config] Add libceph to inclusion list
  * [Config] Drop all inclusion list modules with unsatisfied dependencies
  * SAUCE: (no-up) Remove emi62 files duplicated in linux-firmware
  * SAUCE: (no-up) Remove emi26 files duplicated in linux-firmware
  * SAUCE: (no-up) Remove whiteheat files duplicated in linux-firmware
  * Release Tracking Bug
    - LP: #1168040

  [ Upstream Kernel Changes ]

  * TTY: do not update atime/mtime on read/write
    - LP: #1097680
    - CVE-2013-0160
  * KVM: x86: Convert MSR_KVM_SYSTEM_TIME to use gfn_to_hva_cache functions
    (CVE-2013-1797)
    - LP: #1158258
    - CVE-2013-1797
  * KVM: Fix bounds checking in ioapic indirect register reads
    (CVE-2013-1798)
    - LP: #1158262
    - CVE-2013-1798
  * drm/i915: HDMI/DP - ELD info refresh support for Haswell
    - LP: #1011438
  * ALSA - HDA: New PCI ID for Haswell ULT
    - LP: #1011438
  * ALSA: hda - Support rereading widgets under the function group
    - LP: #1011438
  * ALSA: hda - Add fixup for Haswell to enable all pin and convertor
    widgets
    - LP: #1011438
  * libata: fix DMA to stack in reading devslp_timing parameters
    - LP: #1031173
  * dmaengine: dw_dmac: remove CLK dependency
    - LP: #1031163
  * dmaengine: dw_dmac: Enhance device tree support
    - LP: #1031163
  * dmaengine: dw_dmac: amend description and indentation
    - LP: #1031163
  * dw_dmac: change dev_printk() to corresponding macros
    - LP: #1031163
  * dw_dmac: don't call platform_get_drvdata twice
    - LP: #1031163
  * dw_dmac: change dev_crit to dev_WARN in dwc_handle_error
    - LP: #1031163
  * dw_dmac: introduce to_dw_desc() macro
    - LP: #1031163
  * dw_dmac: absence of pdata isn't critical when autocfg is set
    - LP: #1031163
  * dw_dmac: check for mapping errors
    - LP: #1031163
  * dw_dmac: remove redundant check
    - LP: #1031163
  * dw_dmac: update tx_node_active in dwc_do_single_block
    - LP: #1031163
  * dma: dw_dmac: add dwc_chan_pause and dwc_chan_resume
    - LP: #1031163
  * dmaengine: introduce is_slave_direction function
    - LP: #1031163
  * dmaengine: add possibility for cyclic transfers
    - LP: #1031163
  * dma: dw_dmac: check direction properly in dw_dma_cyclic_prep
    - LP: #1031163
  * dma: ep93xx_dma: reuse is_slave_direction helpe...

With 3.8.0-18 kernel, brightness control is not working on my XPS13 with raring. Blacklight is on but at minimum, brightness keys do nothin.
Blacklight is perfectly working with kernel 3.8.0-17 and maybe before: on waking from suspend, brightness is restored as before suspending and is adjustable.
So this fix seems to solve the bug for someone, but introduced a new bug for me that I had no problems before.
My laptop is an XPS 13 last model, with full-hd display. I installed raring from scratch and it is booting with uefi.

@Marco, thanks for reporting this. Could I ask you to file a new Launchpad bug against linux 3.8.0-18 for this, so that we can capture the hardware profile for that XPS13 model? Please assign the new bug to me.

@Marco, actually this existing bug matches the problem: LP: #1169376. We'll track the problem there.

The verification of this Stable Release Update has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regresssions.

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed' to 'verification-done'.

If verification is not done by one week from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

Re-verified:
Quantal 3.5.0-40.62
Raring 3.8.0-30.44

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-precise' to 'verification-done-precise'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

Verified fixed:
Precise 3.2.0-55.85