[Intel-gfx] i915 warning: WARN_ON_ONCE(!intel_dp->lane_count)

[Daniel Vetter]

On Tue, Dec 13, 2016 at 09:17:50PM +0200, Ville Syrjälä wrote:
> On Tue, Dec 13, 2016 at 11:00:50AM -0800, Linus Torvalds wrote:
> > This isn't new, but I thought I'd report it since it doesn't seem to
> > get fixed on its own..
> > 
> >   [drm] Initialized i915 1.6.0 20161121 for 0000:00:02.0 on minor 0
> >   ------------[ cut here ]------------
> >   WARNING: CPU: 1 PID: 130 at drivers/gpu/drm/i915/intel_dp.c:4018
> > intel_dp_check_link_status+0x1db$
> >   WARN_ON_ONCE(!intel_dp->lane_count)
> >   Modules linked in:
> >    rtsx_pci_sdmmc mmc_core crct10dif_pclmul crc32_pclmul crc32c_intel
> > i915 ghash_clmulni_intel i2c_$
> >   CPU: 1 PID: 130 Comm: kworker/u8:7 Not tainted 4.9.0-04822-g9439b3710df6 #6
> >   Hardware name: Dell Inc. XPS 13 9350/09JHRY, BIOS 1.4.4 06/14/2016
> >   Workqueue: events_unbound async_run_entry_fn
> >   Call Trace:
> >    intel_dp_check_link_status+0x1db/0x200 [i915]
> >    intel_dp_detect+0x697/0xa40 [i915]
> >    drm_helper_probe_single_connector_modes+0x2a3/0x500 [drm_kms_helper]
> >    drm_setup_crtcs+0x7b/0x9c0 [drm_kms_helper]
> >    drm_fb_helper_initial_config+0x79/0x3e0 [drm_kms_helper]
> >    intel_fbdev_initial_config+0x18/0x30 [i915]
> >    async_run_entry_fn+0x37/0x150
> >    process_one_work+0x1f1/0x480
> >    worker_thread+0x48/0x4d0
> >    kthread+0x101/0x140
> >    ret_from_fork+0x22/0x30
> >   ---[ end trace 10162024459bbe32 ]---
> > 
> > That's obviously my XPS13, and it has nothing attached to it, so just
> > the internal laptop display.
> > 
> > This is all intel, with the Skylake Iris Graphics 540 (i7-6560U).
> > 
> > Everything seems to work fine, it's just the ugly warning.
> 
> Yeah, it shouldn't really matter as long as the DP link doesn't fall
> over during boot. If that were to happen we wouldn't be able to
> retrain the link since we didn't copy the link parameters (eg. the
> lane count) to the right place.
> 
> I posted a patch a while back that should fix it, but Daniel didn't
> like it, and it's looking like no one is volunteering to work on it
> further.

Yeah, checked that patch, I still don't like it. I'll throw a patch onto
the pile to remove this WARN_ON and replace it with a FIXME. I'll also
throw a task item onto the new DP team that they need to actually fix this
;-)

Since this isn't a "system on fire" class thing will probably take after
-rc1 (i.e. after holidays) to get through the system.
Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch