[Intel-gfx] [PATCH i-g-t 2/2] test/kms_cursor_crc: align the start of the CRC capture to a vblank

[Arkadiusz Hiler]

On Mon, Jun 22, 2020 at 01:38:26PM -0300, Melissa Wen wrote:
> When running subtests in sequence using vkms, the beginning of CRC capture
> process does not match the simulated vblank timing. This mismatch leads to
> an endless busy wait and, consequently, timeout failures for the remaining
> subtests in the test sequence. This patch sets the pace by waiting for
> vblank before starting the CRC capture.
> 
> Signed-off-by: Melissa Wen <melissa.srw at gmail.com>

This one is quite interetesing. The test seems to be working just fine
on the real hardware and causes the endless busy wait on VKMS only...

DRM is bad at describing usage sequences and what's defined and what's
undefined when it comes to behavior. We just try not to break any of the
existing users. On top of that CRC capture is a testing/debug feature
that doesn't have have to be stable - it's not really obvious what's the
correct course of action here.

The vblank wait won't harm anyone, especially in the context presented
above. You have to keep in mind that other implementations of CRC
caputring doesn't have that requirement and you will likely find more
similar instances of this usage pattern. There may be even more of them
introduced over time - there's no CI on VKMS (fingers crossed that this
is going to change).

Have you thought about what's easier here - making the current code work
on the VKMS side or fixing the test? I would like to know your thoughts
on this.

-- 
Cheers,
Arek




> ---
>  tests/kms_cursor_crc.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/tests/kms_cursor_crc.c b/tests/kms_cursor_crc.c
> index 5976df5f..755c34ed 100644
> --- a/tests/kms_cursor_crc.c
> +++ b/tests/kms_cursor_crc.c
> @@ -474,6 +474,7 @@ static void prepare_crtc(data_t *data, igt_output_t *output,
>  		igt_assert(data->batch);
>  	}
>  
> +	igt_wait_for_vblank(data->drm_fd, data->pipe);
>  	igt_pipe_crc_start(data->pipe_crc);
>  }
>  
> -- 
> 2.27.0
> 
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx