OS: Arch Linux (64 bit) Laptop model: Dell Studio 1555 Graphics card: Radeon HD 4570 HDMI audio stopped working since upgrade to linux kernel 4.0. Reverting to 3.19.3 fixes the issue for me. Tried James's patch from bug 90777 (revert commit 8ffea8570d5a7e9dd3c10349ebc3bd79487ae30b) on kernel 4.1 and it did not help. Tried using the mainline 4.2rc3 kernel and the bug persists.
Make sure your kernel has this patch: https://bugs.freedesktop.org/attachment.cgi?id=116221
Seems I did something wrong last week. Tested again with the same mainline 4.2rc3 and it works.
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