On Mon, 19 Nov 2007, David Brownell wrote:
> Still needs the following update, IMO ...
>
> ====== CUT HERE
> A recent patch added software synchronization during EHCI startup,
> so ports aren't switched away from the companion controllers after
> resets have started. This patch adds a short delay letting hardware
> get a chance to finish that port switching before any new resets begin.
>
> That is, both sides of that hardware race window need to be closed.
>
> Signed-off-by: David Brownell <[email protected]>
> ---
> drivers/usb/host/ehci-hcd.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> --- g26.orig/drivers/usb/host/ehci-hcd.c 2007-11-13 16:07:12.000000000 -0800
> +++ g26/drivers/usb/host/ehci-hcd.c 2007-11-13 16:13:01.000000000 -0800
> @@ -594,12 +594,15 @@ static int ehci_run (struct usb_hcd *hcd
> * from the companions to the EHCI controller. If any of the
> * companions are in the middle of a port reset at the time, it
> * could cause trouble. Write-locking ehci_cf_port_reset_rwsem
> - * guarantees that no resets are in progress.
> + * guarantees that no resets are in progress. After we set CF,
> + * a short delay lets the hardware catch up; new resets shouldn't
> + * start before the port switching actions complete.
> */
> down_write(&ehci_cf_port_reset_rwsem);
> hcd->state = HC_STATE_RUNNING;
> ehci_writel(ehci, FLAG_CF, &ehci->regs->configured_flag);
> ehci_readl(ehci, &ehci->regs->command); /* unblock posted writes */
> + msleep(5);
> up_write(&ehci_cf_port_reset_rwsem);
>
> temp = HC_VERSION(ehci_readl(ehci, &ehci->caps->hc_capbase));
This addition certainly won't hurt. Did we ever get any feedback as to
whether it actually helped?
Alan Stern
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