This is a note to let you know that I've just added the patch titled
xhci: Solve full event ring by increasing TRBS_PER_SEGMENT to 256
to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.
The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the
next -rc kernel release.
If you have any questions about this process, please let me know.
>From 18cc2f4cbbaf825a4fedcf2d60fd388d291e0a38 Mon Sep 17 00:00:00 2001
From: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx>
Date: Thu, 30 Apr 2015 17:16:03 +0300
Subject: xhci: Solve full event ring by increasing TRBS_PER_SEGMENT to 256
Our event ring consists of only one segment, and we risk filling
the event ring in case we get isoc transfers with short intervals
such as webcams that fill a TD every microframe (125us)
With 64 TRB segment size one usb camera could fill the event ring in 8ms.
A setup with several cameras and other devices can fill up the
event ring as it is shared between all devices.
This has occurred when uvcvideo queues 5 * 32TD URBs which then
get cancelled when the video mode changes. The cancelled URBs are returned
in the xhci interrupt context and blocks the interrupt handler from
handling the new events.
A full event ring will block xhci from scheduling traffic and affect all
devices conneted to the xhci, will see errors such as Missed Service
Intervals for isoc devices, and and Split transaction errors for LS/FS
interrupt devices.
Increasing the TRB_PER_SEGMENT will also increase the default endpoint ring
size, which is welcome as for most isoc transfer we had to dynamically
expand the endpoint ring anyway to be able to queue the 5 * 32TDs uvcvideo
queues.
The default size used to be 64 TRBs per segment
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/usb/host/xhci.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/usb/host/xhci.h b/drivers/usb/host/xhci.h
index 8e421b89632d..ea75e8ccd3c1 100644
--- a/drivers/usb/host/xhci.h
+++ b/drivers/usb/host/xhci.h
@@ -1267,7 +1267,7 @@ union xhci_trb {
* since the command ring is 64-byte aligned.
* It must also be greater than 16.
*/
-#define TRBS_PER_SEGMENT 64
+#define TRBS_PER_SEGMENT 256
/* Allow two commands + a link TRB, along with any reserved command TRBs */
#define MAX_RSVD_CMD_TRBS (TRBS_PER_SEGMENT - 3)
#define TRB_SEGMENT_SIZE (TRBS_PER_SEGMENT*16)
--
2.4.0
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