From 727d045d064b7c9a24db3bce9c0485a382cb768b Mon Sep 17 00:00:00 2001 From: Michal Pecio Date: Mon, 18 May 2026 07:32:07 +0200 Subject: [PATCH] usb: core: Fix up Interrupt IN endpoints with bogus wBytesPerInterval Tao Xue found that some common devices violate USB 3.x section 9.6.7 by reporting wBytesPerInterval lower than the size of packets they actually send. I confirmed that AX88179 may set it to 0 and RTL8153 CDC configuration sets it to 8 but sends both 8 and 16 byte packets: S Ii:11:007:3 -115:128 16 < C Ii:11:007:3 0:128 8 = a1000000 01000000 S Ii:11:007:3 -115:128 16 < C Ii:11:007:3 0:128 16 = a12a0000 01000800 00000000 00000000 Most xHCI host controllers neglect interrupt bandwidth reservations and let such devices exceed theirs, some fail the URB with EOVERFLOW. Assume that wBytesPerInterval lower than wMaxPacketSize is bogus and increase it to the worst case maximum on interrupt IN endpoints. This solves xHCI problems and appears to have no other effect. Interrupt transfers are not limited to one interval and drivers submit URBs of class defined size without looking at wBytesPerInterval. Any multi- interval transfer is considered terminated by a packet shorter than wMaxPacketSize regardless of wBytesPerInterval - see USB3 8.10.3. Stay in spec on OUT endpoints and isochronous. No buggy devices are known and we don't want to risk sending more data than the device is prepared to handle or confusing isoc drivers regarding altsetting capacities guaranteed by the device itself. And don't complain when wMaxPacketSize <= wBytesPerInterval < wMaxPacketSize * (bMaxBurst+1) because enabling this seems to be the exact goal of the spec. Reported-and-tested-by: Tao Xue Closes: https://lore.kernel.org/linux-usb/20260402021400.28853-1-xuetao09@huawei.com/ Cc: stable@vger.kernel.org Signed-off-by: Michal Pecio Link: https://patch.msgid.link/20260518073207.5b7d26e7.michal.pecio@gmail.com Signed-off-by: Greg Kroah-Hartman --- drivers/usb/core/config.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c index 417140b012bb..d9171bf7bc88 100644 --- a/drivers/usb/core/config.c +++ b/drivers/usb/core/config.c @@ -191,7 +191,14 @@ static void usb_parse_ss_endpoint_companion(struct device *ddev, int cfgno, (desc->bMaxBurst + 1); else max_tx = 999999; - if (le16_to_cpu(desc->wBytesPerInterval) > max_tx) { + /* + * wBytesPerInterval > max_tx is bogus, but USB3 spec doesn't forbid the opposite. + * Experience shows that wBytesPerInterval < wMaxPacketSize on common interrupt IN + * endpoints is usually bogus too, and recent HCs enforce interrupt BW limits. + */ + if (le16_to_cpu(desc->wBytesPerInterval) > max_tx || + (le16_to_cpu(desc->wBytesPerInterval) < usb_endpoint_maxp(&ep->desc) && + usb_endpoint_is_int_in(&ep->desc))) { dev_notice(ddev, "%s endpoint with wBytesPerInterval of %d in " "config %d interface %d altsetting %d ep %d: " "setting to %d\n", -- 2.47.3