linux-kernel - Re: [PATCH v1 2/2] ASoC: meson: implement link-name optional property in meson card utils

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Date: Mon, 08 Apr 2024 20:42:22 +0200
From: Jerome Brunet <jbrunet@...libre.com>
To: Jerome Brunet <jbrunet@...libre.com>
Cc: Dmitry Rokosov <ddrokosov@...utedevices.com>, neil.armstrong@...aro.org,
 lgirdwood@...il.com, broonie@...nel.org, conor+dt@...nel.org,
 robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org, perex@...ex.cz,
 tiwai@...e.com, khilman@...libre.com, martin.blumenstingl@...glemail.com,
 kernel@...utedevices.com, rockosov@...il.com,
 linux-amlogic@...ts.infradead.org, alsa-devel@...a-project.org,
 linux-sound@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v1 2/2] ASoC: meson: implement link-name optional
 property in meson card utils


On Mon 08 Apr 2024 at 20:15, Jerome Brunet <jbrunet@...libre.com> wrote:

> On Mon 08 Apr 2024 at 19:49, Dmitry Rokosov <ddrokosov@...utedevices.com> wrote:
>
>> The 'link-name' property presents an optional DT feature that empowers
>> users to customize the name associated with the DAI link and PCM stream.
>> This functionality reflects the approach often employed in Qualcomm
>> audio cards, providing enhanced flexibility in DAI naming conventions
>> for improved system integration and userspace experience.
>>
>> It allows userspace program to easy determine PCM stream purpose, e.g.:
>>     ~ # cat /proc/asound/pcm
>>     00-00: speaker (*) :  : playback 1
>>     00-01: mics (*) :  : capture 1
>>     00-02: loopback (*) :  : capture 1
>
> The example above is exactly what you should not do with link names, at
> least with the amlogic audio system.
>
> Userspace pcm, otherwise known as DPCM frontend, are merely that:
> frontends. What they do is entirely defined by the routing defined by
> the userspace (amixer and friends)
>
> So naming the interface in DT (the FW describing the HW) after what the
> the userspace SW could possibly set later on is wrong.
>
> Bottom line: I have mixed feeling about this change. It could allow all
> sort of bad names to be set.
>
> The only way it could make sense HW wise is if the only allowed names
> where (fr|to)ddr_[abcd], which could help maps the interface and the
> kcontrol.
>
> Such restriction should be documented in the binding doc.
>

Thinking about it further, even this does not make a lot of sense.
The information is already available from dai_name, prefixes and all.

Please use that instead if you must rename the userspace pcm, not DT.

>>
>> The previous naming approach using auto-generated fe or be strings
>> continues to be utilized as a fallback.
>>
>> Signed-off-by: Dmitry Rokosov <ddrokosov@...utedevices.com>
>> ---
>>  sound/soc/meson/meson-card-utils.c | 12 ++++++++----
>>  1 file changed, 8 insertions(+), 4 deletions(-)
>>
>> diff --git a/sound/soc/meson/meson-card-utils.c b/sound/soc/meson/meson-card-utils.c
>> index ed6c7e2f609c..7bae72905a9b 100644
>> --- a/sound/soc/meson/meson-card-utils.c
>> +++ b/sound/soc/meson/meson-card-utils.c
>> @@ -94,10 +94,14 @@ static int meson_card_set_link_name(struct snd_soc_card *card,
>>  				    struct device_node *node,
>>  				    const char *prefix)
>>  {
>> -	char *name = devm_kasprintf(card->dev, GFP_KERNEL, "%s.%s",
>> -				    prefix, node->full_name);
>> -	if (!name)
>> -		return -ENOMEM;
>> +	const char *name;
>> +
>> +	if (of_property_read_string(node, "link-name", &name)) {
>> +		name = devm_kasprintf(card->dev, GFP_KERNEL, "%s.%s",
>> +				      prefix, node->full_name);
>> +		if (!name)
>> +			return -ENOMEM;
>> +	}
>>  
>>  	link->name = name;
>>  	link->stream_name = name;


-- 
Jerome