Re: video: X sets brightness to zero after resume

[Aaron Lu <aaron.lu@intel.com>]

On 06/12/2014 08:42 PM, Kalle Valo wrote:
> Hi Aaron,
> 
> after your commit 0e9f81d3b7c ("ACPI / video: Add systems that should
> favour native backlight interface") I have had an regression that every
> time after resume the display brightness has been set to zero and I need
> to manually set it to non-zero to see something again.
> 
> Finally I started to investigate this more closely and it seems that X
> sets it to zero for some reason. I added a WARN_ON() and few printks to
> brightness_store() in drivers/video/backlight/backlight.c and this is
> what I see during resume:
> 
> [   49.228221] ------------[ cut here ]------------
> [   49.228229] WARNING: CPU: 1 PID: 1133 at
> drivers/video/backlight/backlight.c:173 brightness_store+0x3c/0x120(
> )
> [   49.228230] Modules linked in: ctr ccm uvcvideo videobuf2_core
> videodev videobuf2_vmalloc videobuf2_memops fu
> se arc4 iwldvm sha256_generic kvm_intel kvm mac80211 snd_hda_codec_hdmi
> snd_hda_codec_realtek snd_hda_codec_gene
> ric iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 snd_hda_intel
> snd_hda_controller nf_nat_ipv4 nf_nat snd_hda_cod
> ec nf_conntrack snd_hwdep snd_pcm_oss iwlwifi snd_mixer_oss snd_pcm
> ip_tables x_tables thinkpad_acpi snd_seq_dum
> my snd_seq_oss snd_seq_midi snd_rawmidi snd_seq_midi_event snd_seq
> cfg80211 snd_timer snd_seq_device snd bnep rfcomm bluetooth psmouse
> soundcore nvram ehci_pci ehci_hcd rfkill wmi binfmt_misc ext4 jbd2
> mbcache sd_mod fbcon tileblit font bitblit softcursor i915
> drm_kms_helper drm cfbcopyarea i2c_algo_bit intel_gtt agpgart i2c_core
> video xhci_hcd cfbimgblt cfbfillrect e1000e sdhci_pci sdhci ptp pps_core
> mmc_core ahci libahci
> [   49.228281] CPU: 1 PID: 1133 Comm: Xorg Tainted: G        W
> 3.15.0-rc7-wl-ath+ #259
> [   49.228282] Hardware name: LENOVO 2324JB2/2324JB2, BIOS G2ET82WW
> (2.02 ) 09/11/2012
> [   49.228283]  0000000000000000 ffffffff817e4000 ffffffff814cbee3
> 0000000000000000
> [   49.228285]  ffffffff810493bc ffff88020e2d1c98 ffff880213bc9f10
> 0000000000000002
> [   49.228287]  ffff8800c5dfc198 ffff88020d7cbf50 ffffffff81290a1c
> ffff88020e792800
> [   49.228288] Call Trace:
> [   49.228293]  [<ffffffff814cbee3>] ? dump_stack+0x41/0x51
> [   49.228296]  [<ffffffff810493bc>] ? warn_slowpath_common+0x8c/0xc0
> [   49.228298]  [<ffffffff81290a1c>] ? brightness_store+0x3c/0x120
> [   49.228301]  [<ffffffff811d7242>] ? kernfs_fop_write+0x112/0x170
> [   49.228304]  [<ffffffff8116791b>] ? vfs_write+0xcb/0x1f0
> [   49.228306]  [<ffffffff81167e20>] ? SyS_write+0x50/0xb0
> [   49.228308]  [<ffffffff814dd312>] ? system_call_fastpath+0x16/0x1b
> [   49.228309] ---[ end trace a1f60d12df64bdbe ]---
> [   49.228310] brightness=0
> [   49.228310] set brightness to 0
> 
> And this is PID 1133:
> 
> root      1133  0.7  0.2 131504 20192 tty7     Ss+  15:16   0:00
> /usr/bin/X :0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7
> -novtswitch -background none
> 
> If I set video.use_native_backlight=0 in kernel command line the problem
> goes away. Or if I revert your commit 0e9f81d3b7c the problem also goes
> away. Any ideas?

Not really...
I've added i915 people maybe they have an idea.

BTW, there is a simpler way to see who did the brightness store:
# echo 'module backlight +pft' > /sys/kernel/debug/dynamic_debug/control

Thanks,
Aaron

> 
> My setup is:
> 
> Thinkpad X230
> Ubuntu 12.04 64-bit
> i3 window manager
> xserver-xorg 1:7.6+12ubuntu2
>