tilcdc: vblank wait timed out

[Bartosz Golaszewski]

2016-12-05 12:01 GMT+01:00 Bartosz Golaszewski <bgolaszewski at baylibre.com>:
> Hi Jyri,
>
> I pulled your recent tilcdc pull request on top of v4.9 and Sekhar's
> davinci branch (+ vga dac DT)[1].
>
> I'm getting "vblank wait timed out" errors when running simple modetest[2].
>
> This error happened before with the drm_bridge series[3], but went
> away at one of the subsequent patch versions.
>
> Could you please verify that you see the same error and advise on what
> could be the reason? I'm investigating on my own as well.
>
> Best regards,
> Bartosz Golaszewski
>
> [1] https://github.com/brgl/linux/tree/tilcdc/modetest_error
> [2] http://pastebin.com/rCM44Uds
> [3] http://www.spinics.net/lists/dri-devel/msg123732.html

This seems like some END_OF_FRAME0 interrupt-related race condition.
Increasing the timeout in drm_atomic_helper_wait_for_vblanks() from 50
to 100 and dropping drm_modeset_lock_crtc()/drm_modeset_unlock_crtc()
in tilcdc_crtc_recover_work() makes the warning disappear. Also:
calling drm_crtc_vblank_off() additionally before locking the crtc in
tilcdc_crtc_recover_work() also seems to fix the issue 90% of times. I
have been unable to figure out a reliable solution today though.

Best regards,
Bartosz Golaszewski