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SubjectRe: [PATCH v7 06/33] ASoC: Add SOC USB APIs for adding an USB backend
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Hi Mark,

On 9/27/2023 7:48 AM, Mark Brown wrote:
> On Thu, Sep 21, 2023 at 02:48:16PM -0700, Wesley Cheng wrote:
>
>> +static struct device_node *snd_soc_find_phandle(struct device *dev)
>> +{
>> + struct device_node *node;
>> +
>> + node = of_parse_phandle(dev->of_node, "usb-soc-be", 0);
>
> Very nitpicky but this function possibly wants a _usb_ in the name, not
> that it *super* matters with it being static. Or it could just be
> inlined into the only user and not worry about the naming at all.
>

Thanks for the review! Sure, let me reshuffle things around a bit and
just get rid of this function entirely and inline it to the API below.

>> +/**
>> + * snd_soc_usb_get_priv_data() - Retrieve private data stored
>> + * @dev: device reference
>> + *
>> + * Fetch the private data stored in the USB SND SOC structure.
>> + *
>> + */
>> +void *snd_soc_usb_get_priv_data(struct device *dev)
>> +{
>> + struct snd_soc_usb *ctx;
>> +
>> + ctx = snd_soc_find_usb_ctx(dev);
>> + if (!ctx) {
>> + /* Check if backend device */
>> + mutex_lock(&ctx_mutex);
>> + list_for_each_entry(ctx, &usb_ctx_list, list) {
>> + if (dev->of_node == ctx->dev->of_node) {
>> + mutex_unlock(&ctx_mutex);
>> + goto out;
>> + }
>> + }
>> + mutex_unlock(&ctx_mutex);
>> + ctx = NULL;
>> + }
>
> This seems a lot more expensive than I'd expect for a get_priv_data
> operation, usually it's just a container_of() or other constant time
> pulling out of a pointer rather than a linked list walk - the sort of
> thing that people put at the start of functions and do all the time.
> If we need this I think it needs a name that's more clearly tied to the
> use case.
>
> I didn't actually find the user of this though?

So the end user of this would be the qc_audio_offload driver, within
prepare_qmi_response(). This is to fetch some information about the
DPCM backend during the stream enable request.

Previously, I limited the # of snd_soc_usb ports to be registered to
one, but that would affect the scalability of this layer. Hence, adding
a list instead increased the complexity. Will rename this accordingly.

Thanks
Wesley Cheng

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