linux-kernel - Re: [PATCH v3] sound/soc/adi/axi-spdif.c: Support programmable master clock

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Date:	Thu, 18 Dec 2014 16:07:53 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Mike Looijmans <mike.looijmans@...ic.nl>
CC:	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] sound/soc/adi/axi-spdif.c: Support programmable master
 clock

On 12/11/2014 08:44 AM, Mike Looijmans wrote:
> If the master clock supports programmable rates, program it to generate
> the desired frequency. Only apply constraints when the clock is fixed.
> This allows proper clock generation for both 44100 and 48000 Hz based
> sampling rates if the platform supports it.
>
> The clock frequency must be set before enabling it. Enabling the clock
> was done in "startup", but that occurs before "hw_params" where the rate
> is known. Enabling a programmable clock without first setting a valid
> frequency may harm the system. Move the clock start to the hw_params
> routine, and keep track of whether the clock has been started, because
> shutdown may be called without having called hw_params first, and
> hw_params may be called multiple times.
> Starting the clock and enabling the SPDIF output AFTER programming the
> dividers is a more logical order anyway.
>
> To detect if the source clock is fixed, the driver calls clk_round_rate
> for two frequencies. If the results are equal, or if the call returns
> an error, the driver assumes the clock is fixed.
>
> Signed-off-by: Mike Looijmans <mike.looijmans@...ic.nl>

Acked-by: Lars-Peter Clausen <lars@...afoo.de>

Thanks.
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