USB: EHCI: slow down ITD reuse

Currently ITDs are immediately recycled whenever their URB completes.
However, EHCI hardware can sometimes remember some ITD state.  This
means that when the ITD is reused before end-of-frame it may sometimes
cause the hardware to reference bogus state.

This patch defers reusing such ITDs by moving them into a new ehci member
cached_itd_list. ITDs resting in cached_itd_list are moved back into their
stream's free_list once scan_periodic() detects that the active frame has
elapsed.

This makes the snd_usb_us122l driver (in kernel since .28) work right
when it's hooked up through EHCI.

[ dbrownell@users.sourceforge.net: comment fixups ]

Signed-off-by: Karsten Wiese <fzu@wemgehoertderstaat.de>
Tested-by: Philippe Carriere <philippe-f.carriere@wanadoo.fr>
Tested-by: Federico Briata <federicobriata@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 4725d15d096f..e551bb38852b 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -485,6 +485,7 @@ static int ehci_init(struct usb_hcd *hcd)
          * periodic_size can shrink by USBCMD update if hcc_params allows.
          */
         ehci->periodic_size = DEFAULT_I_TDPS;
+        INIT_LIST_HEAD(&ehci->cached_itd_list);
         if ((retval = ehci_mem_init(ehci, GFP_KERNEL)) < 0)
                 return retval;
 
@@ -497,6 +498,7 @@ static int ehci_init(struct usb_hcd *hcd)
 
         ehci->reclaim = NULL;
         ehci->next_uframe = -1;
+        ehci->clock_frame = -1;
 
         /*
          * dedicate a qh for the async ring head, since we couldn't unlink