On Mon 08 Apr 2024 at 20:15, Jerome Brunet <jbrunet@xxxxxxxxxxxx> wrote:
> On Mon 08 Apr 2024 at 19:49, Dmitry Rokosov <ddrokosov@xxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxx>
>> ---
>> 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
