Santa doesn't forget about old cards (R6xx/R7xx HDMI audio)

Since ever few radeon HDMI audio testers were reporting problems with their TVs not displaying anything at all. Enabling audio support resulted in invalid signal or similar error.

Thanks to great help from Nirbheek Chauhan, I've finally found the source of this issue. It appears we calculate checksum of HDMI infoframe incorrectly. Some TVs don't care about this, but others really do, refusing to display or play anything.

I've just posted:
[PATCH] drm/radeon/kms: workaround invalid AVI infoframe checksum
with suggestion of backporting this patch to stable releases. Just a one another Christmas gift from me.

Merry Christmas everyone who celebrate it :)