linux-kernel - Re: [alsa-devel] [PATCH v3 4/5] ASoC: tda998x: adjust the audio hw parameters from EDID

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Date:	Wed, 05 Feb 2014 10:19:22 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Jean-Francois Moine <moinejf@...e.fr>
CC:	Mark Brown <broonie@...nel.org>, alsa-devel@...a-project.org,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	Rob Clark <robdclark@...il.com>,
	Dave Airlie <airlied@...il.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [alsa-devel] [PATCH v3 4/5] ASoC: tda998x: adjust the audio hw
 parameters from EDID

On 02/05/2014 10:11 AM, Jean-Francois Moine wrote:
> On Tue, 4 Feb 2014 18:06:25 +0000
> Mark Brown <broonie@...nel.org> wrote:
>
>> On Mon, Jan 27, 2014 at 09:48:54AM +0100, Jean-Francois Moine wrote:
>>
>>> +		/* change the snd_soc_pcm_stream values of the driver */
>>> +		stream->rates = rate_mask;
>>> +		stream->channels_max = max_channels;
>>> +		stream->formats = formats;
>>
>>> +	/* copy the DAI driver to a writable area */
>>> +	dai_drv = devm_kzalloc(&pdev->dev, sizeof(tda998x_dai), GFP_KERNEL);
>>> +	if (!dai_drv)
>>> +		return -ENOMEM;
>>> +	memcpy(dai_drv, tda998x_dai, sizeof(tda998x_dai));
>>> +
>>
>> The code should be doing this by setting constraints based on the
>> current setup rather than by editing the data structure - the expecation
>> is very much that the data won't change so this prevents surprises with
>> future work on the core.
>
> As it is done in the soc core, in soc_pcm_open(), the runtime hw_params
> are initialized after the call to the CODEC startup, and the next CODEC
> event is hw_params() when the user has already chosen all the parameters.
>
> So, in the CODEC, I don't see how I could update the parameters
> dictated by the EDID otherwise in changing the DAI driver parameters.
>

The startup function is the right place. But instead of modifying the DAI 
use snd_pcm_hw_constraint_mask64(), snd_pcm_hw_constraint_list(), etc. to 
setup the additional constraints that come from the EDID.

Bonus points for making this a generic helper function that takes a runtime 
and a EDID and then applies the EDID constraints on the runtime.

- Lars
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