On 5/24/19 2:58 AM, Takashi Iwai wrote:
On Fri, 24 May 2019 01:39:45 +0200,
Pierre-Louis Bossart wrote:
This is the second take on same problem of detecting when the HDaudio
legacy driver can be used and when the SST or SOF drivers are
required.
The previous attempt based on a the PCI Class information was a
resounding failure and broke audio on Linus' laptop, so we need
additional information to avoid enabling a DSP-based driver without a
good reason to do so.
This patchset suggests the use of the NHLT information which *in
theory* exposes DMIC endpoints. The legacy HDaudio driver cannot
handle DMICs and will not provide any capture capabilities. Since it's
typically the first one to probe due to the Makefile order, aborting
the probe will let the PCI subsystem look for the next driver which
hopefully will support this capability.
I tested this patch on 5 devices (SKL, KBL, APL, GLK, WHL), three
without DMICs and two with, and the detection seems to work as
planned. I would appreciate it if HDaudio integrators and folks at
Google/Canonical/Endless can give this a try. As usual I expect that
we will have to use quirks and work-arounds, but it'd be a better idea
than a build-time mutual exclusion. We could also make this optional
(Kconfig and/or module parameters) if people prefer to muck with
blacklists.
Feedback and comments welcome!
The general idea and suggested implementation look almost good to me.
Of course we have to provide a way to override the default behavior in
case of buggy BIOS (I bet a drink for the existence of such :)
I am not sure if it's a good idea to enable this by default, the
experience of the first round showed it's risky to make assumptions on
what BIOS vendors implemented.
I'd rather make this an opt-in solution for distros that have to deal
with this conflict and don't want to use blacklists, and provide both a
Kconfig and kernel parameter to either statically or dynamically enable
this capability. Also this is really needed mostly with WHL+ platforms
where a lot of vendors use DMICs, for previous generations there are
only Chromebooks and a single-digit number of KBL devices.
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