@@ -582,17 +582,16 @@ static int data_ep_set_params(struct snd_usb_endpoint *ep,
ep->stride = frame_bits >> 3;
ep->silence_value = format == SNDRV_PCM_FORMAT_U8 ? 0x80 : 0;
- /* calculate max. frequency */
- if (ep->maxpacksize) {
+ /* 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);
+ /* but wMaxPacketSize might reduce this */
+ if (ep->maxpacksize && ep->maxpacksize < maxsize) {
/* whatever fits into a max. size packet */
maxsize = ep->maxpacksize;
ep->freqmax = (maxsize / (frame_bits >> 3))
<< (16 - ep->datainterval);
- } else {
- /* no max. packet size: just take 25% higher than nominal */
- ep->freqmax = ep->freqn + (ep->freqn >> 2);
- maxsize = ((ep->freqmax + 0xffff) * (frame_bits >> 3))
- >> (16 - ep->datainterval);
}
if (ep->fill_max)
This is a note to let you know that I have just added a patch titled ALSA: usb-audio: do not trust too-big wMaxPacketSize values to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.5.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From 27efaa51591e9659fa534bf307d10d59b5f1ee9d Mon Sep 17 00:00:00 2001 From: Clemens Ladisch <clemens@ladisch.de> Date: Thu, 8 Aug 2013 11:24:55 +0200 Subject: [PATCH] ALSA: usb-audio: do not trust too-big wMaxPacketSize values commit 57e6dae1087bbaa6b33d3dd8a8e90b63888939a3 upstream. The driver used to assume that the streaming endpoint's wMaxPacketSize value would be an indication of how much data the endpoint expects or sends, and compute the number of packets per URB using this value. However, the Focusrite Scarlett 2i4 declares a value of 1024 bytes, while only about 88 or 44 bytes are be actually used. This discrepancy would result in URBs with far too few packets, which would not work correctly on the EHCI driver. To get correct URBs, use wMaxPacketSize only as an upper limit on the packet size. Reported-by: James Stone <jamesmstone@gmail.com> Tested-by: James Stone <jamesmstone@gmail.com> Signed-off-by: Clemens Ladisch <clemens@ladisch.de> Signed-off-by: Takashi Iwai <tiwai@suse.de> [ luis: backported to 3.5: adjusted context ] Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- sound/usb/endpoint.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) -- 1.8.3.2