My rv790 has lost sound over hdmi since -

1518dd8efd47918bb269f1470030592875953f6c is the first bad commit
commit 1518dd8efd47918bb269f1470030592875953f6c
Author: Alex Deucher <alexander.deucher@amd.com>
Date:   Tue Jul 30 17:31:07 2013 -0400

    drm/radeon: fix audio dto calculation on DCE3+ (v3)

    Need to set the wallclock ratio and adjust the phase
    and module registers appropriately.  May fix problems
    with audio timing at certain display timings.

    v2: properly handle clocks below 24mhz
    v3: rebase r600 changes

Tested with 44,1k and 48k source, screen 50Hz.