Re: [PATCH v3 1/6] ASoC: dmaengine: do not use a NULL prepare_slave_config() callback

[Sascha Hauer <sha@pengutronix.de>]

Hi,

On Mon, Mar 07, 2022 at 02:21:57PM +0200, Codrin Ciubotariu wrote:
> Even if struct snd_dmaengine_pcm_config is used, prepare_slave_config()
> callback might not be set. Check if this callback is set before using it.
> 
> Fixes: fa654e085300 ("ASoC: dmaengine-pcm: Provide default config")
> Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
> ---
> 
> Changes in v2,v3:
>  - none
> 
>  sound/soc/soc-generic-dmaengine-pcm.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/sound/soc/soc-generic-dmaengine-pcm.c b/sound/soc/soc-generic-dmaengine-pcm.c
> index 285441d6aeed..2ab2ddc1294d 100644
> --- a/sound/soc/soc-generic-dmaengine-pcm.c
> +++ b/sound/soc/soc-generic-dmaengine-pcm.c
> @@ -86,10 +86,10 @@ static int dmaengine_pcm_hw_params(struct snd_soc_component *component,
>  
>  	memset(&slave_config, 0, sizeof(slave_config));
>  
> -	if (!pcm->config)
> -		prepare_slave_config = snd_dmaengine_pcm_prepare_slave_config;
> -	else
> +	if (pcm->config && pcm->config->prepare_slave_config)
>  		prepare_slave_config = pcm->config->prepare_slave_config;
> +	else
> +		prepare_slave_config = snd_dmaengine_pcm_prepare_slave_config;
>  
>  	if (prepare_slave_config) {
>  		int ret = prepare_slave_config(substream, params, &slave_config);

I wonder if this patch is correct. There are drivers like
sound/soc/mxs/mxs-pcm.c which call snd_dmaengine_pcm_register() with a
config which has the prepare_slave_config callback unset. For these
drivers dmaengine_pcm_hw_params() previously was a no-op. Now with this
patch snd_dmaengine_pcm_prepare_slave_config() and
dmaengine_slave_config() are called. At least for the mxs-pcm driver
calling dmaengine_slave_config() will return -ENOSYS.

At least the "Check if this callback is set before using it" part is
wrong, the callback is checked before using it with

	if (prepare_slave_config) {
		...
	}

I don't have any mxs hardware at hand to test this. I just stumbled upon
the change of behaviour when rebasing
https://patchwork.kernel.org/project/alsa-devel/patch/20220301122111.1073174-1-s.hauer@pengutronix.de/
on current master.

Sascha

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