Re: [RFC PATCH 10/14] sound: usb: card: Check for support for requested audio format

Wesley Cheng
2022-12-27T21:11:35Z

Hi Greg,

On 12/24/2022 12:59 AM, Greg KH wrote:
> On Fri, Dec 23, 2022 at 03:31:56PM -0800, Wesley Cheng wrote:
>> Allow for checks on a specific USB audio device to see if a requested PCM
>> format is supported. This is needed for support for when playback is
>> initiated by the ASoC USB backend path.
>>
>> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
>> ---
>> sound/usb/card.c | 19 +++++++++++++++++++
>> sound/usb/card.h | 3 +++
>> 2 files changed, 22 insertions(+)
>>
>> diff --git a/sound/usb/card.c b/sound/usb/card.c
>> index 396e5a34e23b..9b8d2ed308c8 100644
>> --- a/sound/usb/card.c
>> +++ b/sound/usb/card.c
>> @@ -133,6 +133,25 @@ int snd_usb_unregister_vendor_ops(void)
>> }
>> EXPORT_SYMBOL_GPL(snd_usb_unregister_vendor_ops);
>>
>> +struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
>> + struct snd_pcm_hw_params *params, int direction)
>> +{
>> + struct snd_usb_stream *as;
>> + struct snd_usb_substream *subs = NULL;
>> + const struct audioformat *fmt;
>> +
>> + if (usb_chip[card_idx] && enable[card_idx]) {
>> + list_for_each_entry(as, &usb_chip[card_idx]->pcm_list, list) {
>> + subs = &as->substream[direction];
>> + fmt = find_substream_format(subs, params);
>> + if (fmt)
>> + return as;
>> + }
>> + }
>
> Where is the locking here? How can you walk a list that can be changed
> as you walk it?
>
> And what about reference counting? You are returning a pointer to a
> structure, who now "owns" it? What happens if it is removed from the
> system after you return it?
>
>> + return 0;
>
> Didn't sparse complain about this? You can't return "0" as a pointer,
> it should be NULL.
>
> Always run basic tools like sparse on code before submitting it so that
> we don't have to find errors like this.
>

Got it...I didn't get a chance to run that, but will do it on future
submissions. Will also address the locking and pointer reference you
mentioned.

Thanks
Wesley Cheng