Re: [PATCH v2] ASoC: generic: keep fallback dai_name stable across rebind

[Cássio Gabriel Monteiro Pires]

On 3/27/26 01:11, Cássio Gabriel wrote:
> simple_parse_dai() and graph_util_parse_dai() first try to identify a
> DAI via dai_args. When that works the card can rebind without relying on
> dlc->dai_name.
> 
> The fallback path still calls snd_soc_get_dlc(), which returns a
> borrowed dai_name pointer. If the CPU or codec component is unbound
> while the sound card stays registered, the generic card keeps that
> pointer and the next rebind may compare stale memory while matching the
> DAI.
> 
> Stage the fallback result in a temporary dai_link_component and move
> only a card-owned copy of dai_name into the live link component. Use
> devm_kstrdup_const() so static names are reused and dynamic ones remain
> valid for the lifetime of the card device.
> 
> Signed-off-by: Cássio Gabriel <cassiogabrielcontato@xxxxxxxxx>
> Acked-by: Kuninori Morimoto <kuninori.morimoto.gx@xxxxxxxxxxx>
> ---
> Changes in v2:
> - Rework simple_parse_dai() and graph_util_parse_dai() to use if/else
>   instead of a non-error goto.
> - Move the fallback snd_soc_get_dlc() handling into the else branch.
> - Link to v1: https://patch.msgid.link/20260326-asoc-generic-fallback-dai-name-rebind-v1-1-ac9da3cbd606@xxxxxxxxx
> ---
>  sound/soc/generic/simple-card-utils.c | 52 ++++++++++++++++-------------------
>  sound/soc/generic/simple-card.c       | 46 ++++++++++++++-----------------
>  2 files changed, 44 insertions(+), 54 deletions(-)
> 
> diff --git a/sound/soc/generic/simple-card-utils.c b/sound/soc/generic/simple-card-utils.c
> index da6353594d61..e5cb602fd248 100644
> --- a/sound/soc/generic/simple-card-utils.c
> +++ b/sound/soc/generic/simple-card-utils.c
> @@ -1128,7 +1128,9 @@ int graph_util_parse_dai(struct simple_util_priv *priv, struct device_node *ep,
>  	struct device *dev = simple_priv_to_dev(priv);
>  	struct device_node *node;
>  	struct of_phandle_args args = {};
> +	struct snd_soc_dai_link_component resolved_dlc = {};
>  	struct snd_soc_dai *dai;
> +	const char *fallback_dai_name;
>  	int ret;
>  
>  	if (!ep)
> @@ -1152,39 +1154,31 @@ int graph_util_parse_dai(struct simple_util_priv *priv, struct device_node *ep,
>  		dlc->of_node  = node;
>  		dlc->dai_name = dai_name;
>  		dlc->dai_args = dai_args;
> +	} else {
> +		/* Get dai->name */
> +		args.np		= node;
> +		args.args[0]	= graph_get_dai_id(ep);
> +		args.args_count	= (of_graph_get_endpoint_count(node) > 1);
>  
> -		goto parse_dai_end;
> -	}
> +		ret = snd_soc_get_dlc(&args, &resolved_dlc);
> +		if (ret < 0)
> +			goto err;
>  
> -	/* Get dai->name */
> -	args.np		= node;
> -	args.args[0]	= graph_get_dai_id(ep);
> -	args.args_count	= (of_graph_get_endpoint_count(node) > 1);
> +		/* Keep fallback dai_name valid across component rebind */
> +		fallback_dai_name = resolved_dlc.dai_name;
> +		if (fallback_dai_name) {
> +			fallback_dai_name = devm_kstrdup_const(dev, fallback_dai_name,
> +							       GFP_KERNEL);
> +			ret = -ENOMEM;
> +			if (!fallback_dai_name)
> +				goto err;
> +		}
>  
> -	/*
> -	 * FIXME
> -	 *
> -	 * Here, dlc->dai_name is pointer to CPU/Codec DAI name.
> -	 * If user unbinded CPU or Codec driver, but not for Sound Card,
> -	 * dlc->dai_name is keeping unbinded CPU or Codec
> -	 * driver's pointer.
> -	 *
> -	 * If user re-bind CPU or Codec driver again, ALSA SoC will try
> -	 * to rebind Card via snd_soc_try_rebind_card(), but because of
> -	 * above reason, it might can't bind Sound Card.
> -	 * Because Sound Card is pointing to released dai_name pointer.
> -	 *
> -	 * To avoid this rebind Card issue,
> -	 * 1) It needs to alloc memory to keep dai_name eventhough
> -	 *    CPU or Codec driver was unbinded, or
> -	 * 2) user need to rebind Sound Card everytime
> -	 *    if he unbinded CPU or Codec.
> -	 */
> -	ret = snd_soc_get_dlc(&args, dlc);
> -	if (ret < 0)
> -		goto err;
> +		dlc->of_node = resolved_dlc.of_node;
> +		dlc->dai_name = fallback_dai_name;
> +		dlc->dai_args = resolved_dlc.dai_args;
> +	}
>  
> -parse_dai_end:
>  	if (is_single_link)
>  		*is_single_link = of_graph_get_endpoint_count(node) == 1;
>  	ret = 0;
> diff --git a/sound/soc/generic/simple-card.c b/sound/soc/generic/simple-card.c
> index 9937a991846e..b24ba1330896 100644
> --- a/sound/soc/generic/simple-card.c
> +++ b/sound/soc/generic/simple-card.c
> @@ -69,7 +69,9 @@ static int simple_parse_dai(struct simple_util_priv *priv,
>  {
>  	struct device *dev = simple_priv_to_dev(priv);
>  	struct of_phandle_args args;
> +	struct snd_soc_dai_link_component resolved_dlc = {};
>  	struct snd_soc_dai *dai;
> +	const char *fallback_dai_name;
>  	int ret;
>  
>  	if (!node)
> @@ -94,34 +96,28 @@ static int simple_parse_dai(struct simple_util_priv *priv,
>  		dlc->dai_args = snd_soc_copy_dai_args(dev, &args);
>  		if (!dlc->dai_args)
>  			goto end;
> +	} else {
> +		ret = snd_soc_get_dlc(&args, &resolved_dlc);
> +		if (ret < 0)
> +			goto end;
>  
> -		goto parse_dai_end;
> -	}
> +		/* Keep fallback dai_name valid across component rebind */
> +		fallback_dai_name = resolved_dlc.dai_name;
> +		if (fallback_dai_name) {
> +			fallback_dai_name = devm_kstrdup_const(dev, fallback_dai_name,
> +							       GFP_KERNEL);
> +			ret = -ENOMEM;
> +			if (!fallback_dai_name) {
> +				of_node_put(resolved_dlc.of_node);
> +				goto end;
> +			}
> +		}
>  
> -	/*
> -	 * FIXME
> -	 *
> -	 * Here, dlc->dai_name is pointer to CPU/Codec DAI name.
> -	 * If user unbinded CPU or Codec driver, but not for Sound Card,
> -	 * dlc->dai_name is keeping unbinded CPU or Codec
> -	 * driver's pointer.
> -	 *
> -	 * If user re-bind CPU or Codec driver again, ALSA SoC will try
> -	 * to rebind Card via snd_soc_try_rebind_card(), but because of
> -	 * above reason, it might can't bind Sound Card.
> -	 * Because Sound Card is pointing to released dai_name pointer.
> -	 *
> -	 * To avoid this rebind Card issue,
> -	 * 1) It needs to alloc memory to keep dai_name eventhough
> -	 *    CPU or Codec driver was unbinded, or
> -	 * 2) user need to rebind Sound Card everytime
> -	 *    if he unbinded CPU or Codec.
> -	 */
> -	ret = snd_soc_get_dlc(&args, dlc);
> -	if (ret < 0)
> -		goto end;
> +		dlc->of_node = resolved_dlc.of_node;
> +		dlc->dai_name = fallback_dai_name;
> +		dlc->dai_args = resolved_dlc.dai_args;
> +	}
>  
> -parse_dai_end:
>  	if (is_single_link)
>  		*is_single_link = !args.args_count;
>  	ret = 0;
> 
> ---
> base-commit: d084fd53a2fd5748d4317635b1c1a7dba7edf583
> change-id: 20260326-asoc-generic-fallback-dai-name-rebind-6381a1c807fd
> 
> Best regards,
> --  
> Cássio Gabriel <cassiogabrielcontato@xxxxxxxxx>
> 

I forgot to add the 'Suggested-by' tag attributing
the suggestion made by Kuninori. I apologize.

Should I send a v3 patch adding the tag?

-- 
Thanks,
Cássio