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usb: gadget: dummy_hcd: set no_sg_constraint only on the SuperSpeed bus

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dummy_hcd registers two separate root hubs/buses: a HighSpeed one
emulating an EHCI-class controller, and a SuperSpeed one emulating an
xHCI-class controller.  usb_submit_urb() rejects SG URBs whose
non-final segments are not a multiple of the endpoint maxpacket size,
unless the bus has no_sg_constraint set.

For SuperSpeed bulk endpoints maxpacket is 1024 bytes; usbtest
generates SG lists with varying segment sizes (e.g. 512 bytes) that
are valid transfers but not maxpacket-aligned, causing usb_submit_urb
to return -EINVAL before the URB reaches the host controller.

xHCI-class controllers have no such DMA alignment requirement, so set
no_sg_constraint on the SS bus to match.  Leave the HS bus unchanged:
EHCI-class controllers do have this requirement in hardware, and
dummy_hcd's HS roothub is meant to emulate that behaviour, so the
constraint should stay enforced there.

Suggested-by: Alan Stern <stern@rowland.harvard.edu>
Assisted-by: OpenCode:claude-sonnet-5
Signed-off-by: Igor Skalkin <igor.skalkin@oss.qualcomm.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://patch.msgid.link/20260812081910.6821-3-igor.skalkin@oss.qualcomm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Igor Skalkin 2026-08-12 10:19:10 +02:00 committed by Greg Kroah-Hartman
parent e68f245bcb
commit 8d22d6da17
1 changed files with 9 additions and 0 deletions
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9
drivers/usb/gadget/udc/dummy_hcd.c
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@ -2596,6 +2596,15 @@ static int dummy_setup(struct usb_hcd *hcd)
dum->ss_hcd->dum = dum;
hcd->speed = HCD_USB3;
hcd->self.root_hub->speed = USB_SPEED_SUPER;
/*
* xHCI-class SuperSpeed controllers have no maxpacket
* alignment requirement for non-final SG segments. Only
* relax the constraint on the SS bus; the HS bus keeps
* emulating the alignment requirement of EHCI-class
* controllers.
*/
hcd->self.no_sg_constraint = 1;
}
return 0;
}