From b05dadb28f8779898229e399c21e5192c24beaf2 Mon Sep 17 00:00:00 2001 From: Mathias Nyman Date: Fri, 29 Jan 2021 15:00:31 +0200 Subject: [PATCH] xhci: flush endpoint start to reduce race risk with stop endpoint command. Stop endpoint command fails with "context state error" if the endpoint is already stopped. This case was observed when a previous URB cancel had just completed and rang the doorbell to restart the ring, when a new URB cancel queued a stop endpoint command. >From xHC hardware pov the endpoint had not yet started, so the stop endpoint command failed with context state error. Right after this the doorbell ring took effect and ring was restarted. Interrupt handler saw a stop endpoint command completion event with "context state error" and discovered that the ring was back up in running state. flushing the write reduces these cases in stress testing, but does not completely remove the issue. Signed-off-by: Mathias Nyman Link: https://lore.kernel.org/r/20210129130044.206855-15-mathias.nyman@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- drivers/usb/host/xhci-ring.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c index 2cbdc45..d9714ce 100644 --- a/drivers/usb/host/xhci-ring.c +++ b/drivers/usb/host/xhci-ring.c @@ -429,9 +429,8 @@ void xhci_ring_ep_doorbell(struct xhci_hcd *xhci, trace_xhci_ring_ep_doorbell(slot_id, DB_VALUE(ep_index, stream_id)); writel(DB_VALUE(ep_index, stream_id), db_addr); - /* The CPU has better things to do at this point than wait for a - * write-posting flush. It'll get there soon enough. - */ + /* flush the write */ + readl(db_addr); } /* Ring the doorbell for any rings with pending URBs */ -- 2.7.4