[Intel-gfx] [PATCH v2] drm/i915/vlv: enable HDMI audio for Valleyview2

[Daniel Vetter]

On Fri, Nov 01, 2013 at 03:13:17PM +0000, Lin, Mengdong wrote:
> > Maybe we could use the port CRC stuff to make sure that audio is actually
> > working ...
> 
> Would you please clarify what's port CRC stuff?

The hw has a bunch of CRC (checksum) functions. We've just enabled it at
the pipe level, and it's extremely useful to test whether e.g. the cursor
is displaying properly or whether it's not shown at all. We've had a few
bugs where the cursor was disabled but shouldnt have been.

For an example of such a testcase see i-g-t/tests/kms_cursor_crc.c. This
is all really new, so still in flux.

Now the hardware also has checksum support for each port, and afaik that
includes the audio stream. Iirc never platforms even have special CRCs for
the individual audio streams. My idea for a testcase would be to expose
these port CRCs. Then check that the CRC is stable for each display frame
while no audio is playing, and that it changes (and that the right port
starts to change) once we play an audio stream.

We can't test sync issues with that, but routing issues (which seems to
have been the issue here, and I've also seen a few patches for routing
issues in the past) should be testable. And with an automated testcase we
can ensure that no regression creps in.

The other upside of an automated test like that is that it should be easy
to test all port combinations. That's more important for desktop platforms
where we have 3 HDMI/DP ports.

Anyway I've just thought I'll bring this up as an idea to look into for
the next hw enabling project. It was a bit an effort to enable pipe CRCs
for display testing, but I think long-term it will definitely be worth it.
So maybe poke the audio hw engineers/validation ppl a bit and inquire
whether/how exactly they use this? We've had a display micro architect
help us out a bit on the display side.

Cheers, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch