tree 3f96789f16329d9053f02c0699a3eb48b4f28e62
parent ddb6b5a964371e8e52e696b2b258bda144c8bd3f
author Clemens Ladisch <clemens@ladisch.de> 1375953895 +0200
committer Takashi Iwai <tiwai@suse.de> 1375954654 +0200

ALSA: usb-audio: do not trust too-big wMaxPacketSize values

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>
Cc: <stable@vger.kernel.org> # 2.6.35+
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>