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

[Ville Syrjälä]

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.

-- 
Ville Syrjälä
Intel OTC