On Sat, Aug 08, 2020 at 09:09:00AM -0300, Melissa Wen wrote:
> VKMS needs vblank interrupts enabled to capture CRC. When vblank is
> disabled, tests like kms_cursor_crc and kms_pipe_crc_basic getting stuck
> waiting for a capture that will not occur until vkms wakes up. This patch
> adds a helper to set composer and ensure that vblank remains enabled as
> long as the CRC capture is needed.
>
> It clears the execution of the following kms_cursor_crc subtests:
> 1. pipe-A-cursor-[size,alpha-opaque, NxN-(on-screen, off-screen, sliding,
> random, fast-moving])] - successful when running individually.
> 2. pipe-A-cursor-dpms passes again
> 3. pipe-A-cursor-suspend also passes
>
> The issue was initially tracked in the sequential execution of IGT
> kms_cursor_crc subtests: when running the test sequence or one of its
> subtests twice, the odd execs complete and the pairs get stuck in an
> endless wait. In the IGT code, calling a wait_for_vblank on preparing for
> CRC capture prevented the busy-wait. But the problem persisted in the
> pipe-A-cursor-dpms and -suspend subtests.
>
> Checking the history, the pipe-A-cursor-dpms subtest was successful when,
> in vkms_atomic_commit_tail, instead of using the flip_done op, it used
> wait_for_vblanks. Another way to prevent blocking was wait_one_vblank when
> enabling crtc. However, in both cases, pipe-A-cursor-suspend persisted
> blocking in the 2nd start of CRC capture, which may indicate that
> something got stuck in the step of CRC setup. Indeed, wait_one_vblank in
> the crc setup was able to sync things and free all kms_cursor_crc
> subtests. Besides, other alternatives to force enabling vblanks or prevent
> disabling them such as calling drm_crtc_put_vblank or modeset_enables
> before commit_planes + offdelay = 0, also unlock all subtests executions.
>
> Finally, due to vkms's dependence on vblank interruptions to perform
> tasks, this patch uses refcount to ensure that vblanks happen when
> enabling composer and while crc capture is needed.
>
> Cc: Rodrigo Siqueira <rodrigosiqueiramelo@xxxxxxxxx>
> Cc: Haneen Mohammed <hamohammed.sa@xxxxxxxxx>
>
> Co-debugged-by: Sidong Yang <realwakka@xxxxxxxxx>
> Signed-off-by: Sidong Yang <realwakka@xxxxxxxxx>
> Signed-off-by: Melissa Wen <melissa.srw@xxxxxxxxx>
> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
>
> ---
>
> v2:
> - extract a vkms_set_composer helper
> - fix vblank refcounting for the disabling case
>
> v3:
> - make the vkms_set_composer helper static
> - review the credit tags
Thanks a lot for your work here, patch merged to drm-misc-next.
I've kept the changelog in the commit message, I often find that quite
useful. But that's a bit a drm peculiarity, most other subsystems prefer
it like you've done it.
Cheers, Daniel
>
> ---
> drivers/gpu/drm/vkms/vkms_composer.c | 20 +++++++++++++++++---
> 1 file changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
> index b8b060354667..4f3b07a32b60 100644
> --- a/drivers/gpu/drm/vkms/vkms_composer.c
> +++ b/drivers/gpu/drm/vkms/vkms_composer.c
> @@ -233,6 +233,22 @@ int vkms_verify_crc_source(struct drm_crtc *crtc, const char *src_name,
> return 0;
> }
>
> +static void vkms_set_composer(struct vkms_output *out, bool enabled)
> +{
> + bool old_enabled;
> +
> + if (enabled)
> + drm_crtc_vblank_get(&out->crtc);
> +
> + spin_lock_irq(&out->lock);
> + old_enabled = out->composer_enabled;
> + out->composer_enabled = enabled;
> + spin_unlock_irq(&out->lock);
> +
> + if (old_enabled)
> + drm_crtc_vblank_put(&out->crtc);
> +}
> +
> int vkms_set_crc_source(struct drm_crtc *crtc, const char *src_name)
> {
> struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
> @@ -241,9 +257,7 @@ int vkms_set_crc_source(struct drm_crtc *crtc, const char *src_name)
>
> ret = vkms_crc_parse_source(src_name, &enabled);
>
> - spin_lock_irq(&out->lock);
> - out->composer_enabled = enabled;
> - spin_unlock_irq(&out->lock);
> + vkms_set_composer(out, enabled);
>
> return ret;
> }
> --
> 2.27.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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