ALSA: snd-usb: fix calls to next_packet_size

In order to support devices with implicit feedback streaming models,
packet sizes are now stored with each individual urb, and the PCM
handling code which fills the buffers purely relies on the size fields
now.

However, calling snd_usb_audio_next_packet_size() for all possible
packets in an URB at once, prior to letting the PCM code do its job
does in fact not lead to the same behaviour than what the old code did:
The PCM code will break its loop once a period boundary is reached,
consequently using up less packets that it really could.

As snd_usb_audio_next_packet_size() implements a feedback mechanism to
the endpoints phase accumulator, the number of calls to that function
matters, and when called too often, the data rate runs out of bounds.

Fix this by making the next_packet function public, and call it from the
PCM code as before if the packet data sizes are not defined.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Cc: stable@kernel.org [v3.5+]
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index b896c5559524ba40acf78f4ca2800281816e31d8..d6e2bb49c59c52f01288925fa52461eea510e78a 100644 (file)
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -141,7 +141,7 @@ int snd_usb_endpoint_implict_feedback_sink(struct snd_usb_endpoint *ep)
  *
  * For implicit feedback, next_packet_size() is unused.
  */
-static int next_packet_size(struct snd_usb_endpoint *ep)
+int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep)
 {
        unsigned long flags;
        int ret;
@@ -177,15 +177,6 @@ static void retire_inbound_urb(struct snd_usb_endpoint *ep,
                ep->retire_data_urb(ep->data_subs, urb);
 }
 
-static void prepare_outbound_urb_sizes(struct snd_usb_endpoint *ep,
-                                      struct snd_urb_ctx *ctx)
-{
-       int i;
-
-       for (i = 0; i < ctx->packets; ++i)
-               ctx->packet_size[i] = next_packet_size(ep);
-}
-
 /*
  * Prepare a PLAYBACK urb for submission to the bus.
  */
@@ -370,7 +361,6 @@ static void snd_complete_urb(struct urb *urb)
                        goto exit_clear;
                }
 
-               prepare_outbound_urb_sizes(ep, ctx);
                prepare_outbound_urb(ep, ctx);
        } else {
                retire_inbound_urb(ep, ctx);
@@ -857,7 +847,6 @@ int snd_usb_endpoint_start(struct snd_usb_endpoint *ep, int can_sleep)
                        goto __error;
 
                if (usb_pipeout(ep->pipe)) {
-                       prepare_outbound_urb_sizes(ep, urb->context);
                        prepare_outbound_urb(ep, urb->context);
                } else {
                        prepare_inbound_urb(ep, urb->context);

diff --git a/sound/usb/endpoint.h b/sound/usb/endpoint.h
index a8e60c1408e5d227eb2c529a1c6b52d81f3ff7a3..cbbbdf226d66b6fa9eec51fe829a1b03cdd8d518 100644 (file)
--- a/sound/usb/endpoint.h
+++ b/sound/usb/endpoint.h
@@ -21,6 +21,7 @@ int  snd_usb_endpoint_deactivate(struct snd_usb_endpoint *ep);
 void snd_usb_endpoint_free(struct list_head *head);
 
 int snd_usb_endpoint_implict_feedback_sink(struct snd_usb_endpoint *ep);
+int snd_usb_endpoint_next_packet_size(struct snd_usb_endpoint *ep);
 
 void snd_usb_handle_sync_urb(struct snd_usb_endpoint *ep,
                             struct snd_usb_endpoint *sender,

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 5ceb8f1d63fbe00ecf8c643cc35d06419c45f2c9..e80b6687f43ae3851391e670c1df720dd64d3945 100644 (file)
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -1029,6 +1029,7 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
                                 struct urb *urb)
 {
        struct snd_pcm_runtime *runtime = subs->pcm_substream->runtime;
+       struct snd_usb_endpoint *ep = subs->data_endpoint;
        struct snd_urb_ctx *ctx = urb->context;
        unsigned int counts, frames, bytes;
        int i, stride, period_elapsed = 0;
@@ -1040,7 +1041,11 @@ static void prepare_playback_urb(struct snd_usb_substream *subs,
        urb->number_of_packets = 0;
        spin_lock_irqsave(&subs->lock, flags);
        for (i = 0; i < ctx->packets; i++) {
-               counts = ctx->packet_size[i];
+               if (ctx->packet_size[i])
+                       counts = ctx->packet_size[i];
+               else
+                       counts = snd_usb_endpoint_next_packet_size(ep);
+
                /* set up descriptor */
                urb->iso_frame_desc[i].offset = frames * stride;
                urb->iso_frame_desc[i].length = counts * stride;