Re: [alsa-devel] [PATCH] ASoC: rt5640: add master clock handling for rt5640

From: Mark Brown
Date: Thu Feb 25 2016 - 20:09:03 EST

On Wed, Feb 24, 2016 at 10:10:05AM -0600, Pierre-Louis Bossart wrote:
> On 2/23/16 9:32 PM, Mark Brown wrote:

> >That said we really do need x86 to transition to use the clock API
> >in order to integrate with external devices, where the machine driver
> >does manage clocks we want that to move to being done using the clock
> >API rather than custom APIs.

> For Baytrail audio we have a single platform clock that can be turned
> on/off and set to 19.2 MHz or 25 MHz. No other controls are available,
> no multipliers or complicated dependencies on other clocks, parents or
> children and no other users for this clock but the audio subsystem.
> I looked at the clock framework and couldn't figure out how it would simply
> map the hardware so for now the use of the MCLK is only enabled with an
> on/off or set-rate(19.2|25) custom API. I am not an expert here so if this
> clock framework becomes a requirement to upstream code I would appreciate
> any pointers to do the right thing. I really couldn't find a simple example
> with 'Put your code here' comments to use this framework.

There's a lot of helpers like -fixed, -gate and so on - this sounds like
you could probably use those helpers (there should be lots of examples
in the kernel) or just implement a simple provider (see clk-provider.h)
depending on how the control is mapped in. If it's that simple just
open coding a provider ought to do the job. Then set up the client
linkage with clkdev in some way that makes sense for your platform.

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