Good catch!
Is there any chance that Julian's instability after system resume is
related to this bug? If you forced a reset resume, the xHCI driver
would have reallocated the command ring with a proper link TRB. Without
the reset resume, the zeroed command ring wouldn't have a link TRB and
the host controller would have eventually walked off the end of the
command ring. That might explain why the host controller stopped
responding to the stop endpoint command without the reset resume, but
only after a very long time (half an hour).
Julian, can you revert Andiry's patch to add the reset resume, add this
patch instead, and see if it fixes your instability issues? If so, I
think this is a better fix.
Sarah Sharp
On Wed, Nov 30, 2011 at 04:37:41PM +0800, Andiry Xu wrote:
> When system enters suspend, xHCI driver clears command ring by writing zero
> to all the TRBs. However, this also writes zero to the Link TRB, and the ring
> is mangled. This may cause driver accesses wrong memory address and the
> result is unpredicted.
>
> When clear the command ring, keep the last Link TRB intact, only clear its
> cycle bit. This should fix the "command ring full" issue reported by Oliver
> Neukum.
>
> This should be backported to stable kernels as old as 2.6.37, since the
> commit 89821320 "xhci: Fix command ring replay after resume" is merged.
>
> Signed-off-by: Andiry Xu <andiry.xu@xxxxxxx>
> ---
> drivers/usb/host/xhci.c | 5 ++++-
> 1 files changed, 4 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
> index aa94c01..a1afb7c 100644
> --- a/drivers/usb/host/xhci.c
> +++ b/drivers/usb/host/xhci.c
> @@ -711,7 +711,10 @@ static void xhci_clear_command_ring(struct xhci_hcd *xhci)
> ring = xhci->cmd_ring;
> seg = ring->deq_seg;
> do {
> - memset(seg->trbs, 0, SEGMENT_SIZE);
> + memset(seg->trbs, 0,
> + sizeof(union xhci_trb) * (TRBS_PER_SEGMENT - 1));
> + seg->trbs[TRBS_PER_SEGMENT - 1].link.control &=
> + cpu_to_le32(~TRB_CYCLE);
> seg = seg->next;
> } while (seg != ring->deq_seg);
>
> --
> 1.7.4.1
>
>
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