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

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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@xxxxxxxxxxx>
---
  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



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