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

[Cássio Gabriel Monteiro Pires]

On 3/27/26 02:22, Cássio Gabriel Monteiro Pires wrote:
> 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?

I'm going to send a v3 patch with the tag added.

-- 
Thanks,
Cássio