On Tue, 12 Oct 2021 16:29:35 +0200, Kai Vehmanen wrote:
The snd_hdac_bus_reset_link() contains logic to clear STATESTS register before performing controller reset. This code dates back to an old bugfix in commit e8a7f136f5ed ("[ALSA] hda-intel - Improve HD-audio codec probing robustness"). Originally the code was added to azx_reset().
The code was moved around in commit a41d122449be ("ALSA: hda - Embed bus into controller object") and ended up to snd_hdac_bus_reset_link() and called primarily via snd_hdac_bus_init_chip().
The logic to clear STATESTS is correct when snd_hdac_bus_init_chip() is called when controller is not in reset. In this case, STATESTS can be cleared. This can be useful e.g. when forcing a controller reset to retry codec probe. A normal non-power-on reset will not clear the bits.
However, this old logic is problematic when controller is already in reset. The HDA specification states that controller must be taken out of reset before writing to registers other than GCTL.CRST (1.0a spec, 3.3.7). The write to STATESTS in snd_hdac_bus_reset_link() will be lost if the controller is already in reset per the HDA specification mentioned.
This has been harmless on older hardware. On newer generation of Intel PCIe based HDA controllers, if configured to report issues, this write will emit an unsupported request error. If ACPI Platform Error Interface (APEI) is enabled in kernel, this will end up to kernel log.
Fix the code in snd_hdac_bus_reset_link() to only clear the STATESTS if the function is called when controller is not in reset. Otherwise clearing the bits is not possible and should be skipped.
Signed-off-by: Kai Vehmanen kai.vehmanen@linux.intel.com
Do we have a bug reference? I guess it worth to be pushed to 5.15-rc and Cc-to-stable, if this is hitting already on the recent machines.
thanks,
Takashi