Re: [PATCH i-g-t] tests/kms_plane_multiple: CRC based atomic correctness test

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Oct 17, 2016 at 02:28:37PM +0300, Mika Kahola wrote:
> +	for (int i = 0; i < iterations; i++) {
> +		igt_info("%d/%d: Testing connector %s using pipe %s with %d planes\n",
> +			 i+1, iterations, igt_output_name(output),
> +			 kmstest_pipe_name(pipe), max_planes);
> +
> +		test_init(data, pipe);
> +
> +		test_grab_crc(data, output, pipe, &blue, tiling,
> +			      &test.reference_crc);
> +
> +		test_planes(data, pipe, &blue, tiling, max_planes, output);
> +
> +		if (test_atomic) {
> +			igt_display_commit_atomic(&data->display,
> +						  DRM_MODE_PAGE_FLIP_EVENT,
> +						  &data->display);
> +		} else
> +			igt_display_commit2(&data->display, COMMIT_LEGACY);
> +
> +		igt_pipe_crc_start(data->pipe_crc);
> +		n = igt_pipe_crc_get_crcs(data->pipe_crc, 1, &crc);
> +		igt_assert_eq(n, 1);
> +		igt_pipe_crc_stop(data->pipe_crc);

Comment on testing method here: With atomic we don't just require that the
result looks good at the end, but also that _every_ frame is perfect. That
means you need a slightly different test sequence:

1. Enable crc capture.

2. Create a new atomic state (randomized, whatever) which should in the
end still result in the same screen contents using the punchout box trick.
This depends upon the exact subtest.

3. Commit the state from step 2.

4. Wait to make sure the atomic commit has completed. If you do an async
commit, that means waiting for the flip_event to get signalled (didn't see
code for that anywhere).

5. Fetch all the crc values (if there's not a bug in your code or in the
kernel it should be just 1) and make sure they are _all_ the right value.
Your code here only grabs 1 crc after the atomic commit completed, which
means if there's tearing or underruns you'll miss them. Which means it
won't actually validate the crucial feature for which we've created
atomic!

6. Go back to 2.

7. After enough loops, stop crc capturing.

Note that this is the loop for ALLOW_MODESET==false atomic commits, i.e.
where every atomic commit should take at most 1 vblank interval. If any of
the commits take longer than that, there's a bug in either the kernel or
your testcase. Note that crc_start alone has a few vblank waits (due to
crc bugs on some platforms) which will break this.

Cheers, Daniel

> +
> +		igt_assert_crc_equal(&test.reference_crc, crc);
> +
> +		test_fini(data, output, max_planes);
> +	}
> +}
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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