[ALSA] usb-audio: schedule high speed URBs with 1 ms alignment

USB generic driver
The EHCI driver doesn't interrupt more than once per millisecond, and
organizes all iso transfers with frame-sized ITDs, so we can (try to)
be more efficient by aligning all URBs on frame boundaries.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

1 files changed, 14 insertions, 6 deletions

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 49075f06f84..a62d1313da1 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -893,7 +893,7 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
 {
         unsigned int maxsize, n, i;
         int is_playback = subs->direction == SNDRV_PCM_STREAM_PLAYBACK;
-        unsigned int npacks[MAX_URBS], urb_packs, total_packs;
+        unsigned int npacks[MAX_URBS], urb_packs, total_packs, packs_per_ms;
 
         /* calculate the frequency in 16.16 format */
         if (snd_usb_get_speed(subs->dev) == USB_SPEED_FULL)
@@ -920,14 +920,18 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
         else
                 subs->curpacksize = maxsize;
 
+        if (snd_usb_get_speed(subs->dev) == USB_SPEED_HIGH)
+                packs_per_ms = 8 >> subs->datainterval;
+        else
+                packs_per_ms = 1;
+
         if (is_playback) {
                 urb_packs = nrpacks;
                 urb_packs = max(urb_packs, (unsigned int)MIN_PACKS_URB);
                 urb_packs = min(urb_packs, (unsigned int)MAX_PACKS);
         } else
                 urb_packs = 1;
-        if (snd_usb_get_speed(subs->dev) == USB_SPEED_HIGH)
-                urb_packs = (urb_packs * 8) >> subs->datainterval;
+        urb_packs *= packs_per_ms;
 
         /* allocate a temporary buffer for playback */
         if (is_playback) {
@@ -949,8 +953,12 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
                         minsize -= minsize >> 2;
                 minsize = max(minsize, 1u);
                 total_packs = (period_bytes + minsize - 1) / minsize;
-                if (total_packs < 2 * MIN_PACKS_URB)
-                        total_packs = 2 * MIN_PACKS_URB;
+                /* round up to multiple of packs_per_ms */
+                total_packs = (total_packs + packs_per_ms - 1)
+                                & ~(packs_per_ms - 1);
+                /* we need at least two URBs for queueing */
+                if (total_packs < 2 * MIN_PACKS_URB * packs_per_ms)
+                        total_packs = 2 * MIN_PACKS_URB * packs_per_ms;
         } else {
                 total_packs = MAX_URBS * urb_packs;
         }
@@ -972,7 +980,7 @@ static int init_substream_urbs(snd_usb_substream_t *subs, unsigned int period_by
                 subs->nurbs = 2;
                 npacks[0] = (total_packs + 1) / 2;
                 npacks[1] = total_packs - npacks[0];
-        } else if (npacks[subs->nurbs-1] < MIN_PACKS_URB) {
+        } else if (npacks[subs->nurbs-1] < MIN_PACKS_URB * packs_per_ms) {
                 /* the last packet is too small.. */
                 if (subs->nurbs > 2) {
                         /* merge to the first one */