[alsa-devel] [PATCH v2 RESEND 2/2] ASOC: tegra: fix AC97 clock handling

Stephen Warren swarren at wwwdotorg.org
Tue Dec 17 23:33:54 CET 2013

On 12/17/2013 03:28 PM, Mark Brown wrote:
> On Tue, Dec 17, 2013 at 03:20:35PM -0700, Stephen Warren wrote:
>> The Tegra clocking architecture has a shared audio PLL that provides
>> clocks to the various IO controllers (I2S, AC'97, S/PDIF). In order to
>> allow multiple IO controllers to be in use at once, a single SW entity
>> has to manage the clocks, so that it can configure the audio PLL, rather
>> than having each individual IO controller attempt to assert ownership on
>> the shared resource. The centralized PLL management needs to switch the
>> PLL rate between 2 different values for 48-/44.1KHz-based audio for
>> example, and deny requests to switch if already-active audio is running
>> at the other rate.
>> So yes, I think doing this all in the machine driver is the best thing.
> How does doing this in the machine driver help here?  The machine driver
> isn't going to be any more coordinated with other machine drivers than
> the controller is.

There would only be one machine driver loaded at a time. It should
provide top-level control over all the audio paths in the Tegra audio

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