[alsa-devel] [PATCH 1/4] ASOC: tegra: move AC97 clock defines to the controller node

Stephen Warren swarren at wwwdotorg.org
Tue Jul 23 18:47:34 CEST 2013

On 07/21/2013 02:28 PM, Lucas Stach wrote:
> Different from other Tegra sound controllers drivers, the AC97
> controller driver uses the tegra asoc utils directly to request the
> needed clocks, as they are needed at AC97 init time. Move the DT clock
> defines to the right place.

I'm not convinced this is the correct approach.

The machine driver needs to manage these clocks, so that it can
co-ordinate between different audio paths. For example, consider a
system that supports two different I2S paths. In HW, if both are active
at once, these need to both run at a derivative of 48KHz or both run at
a derivative of 44.1KHz. The machine driver is the central place that
enforces that, and should eventually automatically place constraints on
one stream when another is configured for a specific sample rate. By the
same argument, AC'97 can't be a special case here, in case there's some
system with both AC'97 and I2S hooked up.

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