diff options
| -rw-r--r-- | sound/usb/endpoint.c | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c index e6f71894ecdc..a77d9c812dc6 100644 --- a/sound/usb/endpoint.c +++ b/sound/usb/endpoint.c @@ -610,8 +610,23 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep, /* assume max. frequency is 25% higher than nominal */ ep->freqmax = ep->freqn + (ep->freqn >> 2); - maxsize = ((ep->freqmax + 0xffff) * (frame_bits >> 3)) - >> (16 - ep->datainterval); + /* Round up freqmax to nearest integer in order to calculate maximum + * packet size, which must represent a whole number of frames. + * This is accomplished by adding 0x0.ffff before converting the + * Q16.16 format into integer. + * In order to accurately calculate the maximum packet size when + * the data interval is more than 1 (i.e. ep->datainterval > 0), + * multiply by the data interval prior to rounding. For instance, + * a freqmax of 41 kHz will result in a max packet size of 6 (5.125) + * frames with a data interval of 1, but 11 (10.25) frames with a + * data interval of 2. + * (ep->freqmax << ep->datainterval overflows at 8.192 MHz for the + * maximum datainterval value of 3, at USB full speed, higher for + * USB high speed, noting that ep->freqmax is in units of + * frames per packet in Q16.16 format.) + */ + maxsize = (((ep->freqmax << ep->datainterval) + 0xffff) >> 16) * + (frame_bits >> 3); /* but wMaxPacketSize might reduce this */ if (ep->maxpacksize && ep->maxpacksize < maxsize) { /* whatever fits into a max. size packet */ |