[alsa-devel] HD-Audio: How to reduce driver initializaton time if multiple codecs present on the bus?

David Henningsson david.henningsson at canonical.com
Fri Nov 29 08:31:59 CET 2013

2013-11-29 14:40, Takashi Iwai skrev:
> At Fri, 29 Nov 2013 14:30:48 +0800,
> David Henningsson wrote:
>> 2013-11-28 22:57, Lin, Mengdong skrev:
>>> Hi Takashi,
>>> We're trying to reduce the HD-A driver initialization time when more than one codecs are connected to the bus, but are blocked.
>>> Would you please share some advices on this?
>>> Usually, there is one HD-A controller connecting to two codecs: one on-board codec and one integrated display codec.
>>> During initialization, the codecs are created and configured in a serial way.
>>> Creating a codec may cost 6~20ms, and then building controls make cost about 15~30ms.
>> Sorry for interrupting, but I just wonder - I assume you have a maximum
>> of 4 CPUs. Can't the other 3 CPUs be used to load other non-audio
>> hardware in parallel instead? It sounds you're going to run into lock
>> contention instead if you try to modify the same card from two threads
>> simultaneously.
> IIRC, PCI device probes are done sequentially because asynchronous
> probe caused too many troubles.  And if it's a module, it's anyway
> more strictly serialized.

Okay. It just seems to me that from a bird's eye view that parallelizing 
module loading and pci probing would give us much bigger benefits than 
trying to parallellize internally in the snd-hda-intel driver.

Btw, using a deferred azx_probe_continue (like we do if there's a 
firmware file), would one get more parallelization with other drivers? 
If so we could consider making that the default.

David Henningsson, Canonical Ltd.

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