This patch (as1584) fixes a minor bug that has been present in
ehci-hcd since the beginning.
Scanning the schedules for URB completions is single-threaded. If a
completion interrupt occurs while an URB is being given back, the
interrupt handler realizes that a scan is in progress on another CPU
and avoids starting a new one.
This means that completion events can be lost. If an URB completes
after it has been scanned but while a scan is still in progress, the
driver won't notice and won't rescan the completed URB.
The patch fixes the problem by adding a new flag to indicate that
another scan is needed after the current scan is done. The flag gets
set whenever a completion interrupt occurs while a scan is in
progress. The rescan will see the completion, thus preventing it from
getting lost.
Signed-off-by: Alan Stern <st...@rowland.harvard.edu>
---
drivers/usb/host/ehci-hcd.c | 13 ++++++++++---
drivers/usb/host/ehci.h | 3 ++-
2 files changed, 12 insertions(+), 4 deletions(-)
Index: usb-3.4/drivers/usb/host/ehci.h
===================================================================
--- usb-3.4.orig/drivers/usb/host/ehci.h
+++ usb-3.4/drivers/usb/host/ehci.h
@@ -113,7 +113,8 @@ struct ehci_hcd { /* one per controlle
enum ehci_rh_state rh_state;
/* general schedule support */
- unsigned scanning:1;
+ bool scanning:1;
+ bool need_rescan:1;
bool intr_unlinking:1;
bool async_unlinking:1;
Index: usb-3.4/drivers/usb/host/ehci-hcd.c
===================================================================
--- usb-3.4.orig/drivers/usb/host/ehci-hcd.c
+++ usb-3.4/drivers/usb/host/ehci-hcd.c
@@ -400,14 +400,21 @@ static void ehci_work (struct ehci_hcd *
* it reports urb completions. this flag guards against bogus
* attempts at re-entrant schedule scanning.
*/
- if (ehci->scanning)
+ if (ehci->scanning) {
+ ehci->need_rescan = true;
return;
- ehci->scanning = 1;
+ }
+ ehci->scanning = true;
+
+ rescan:
+ ehci->need_rescan = false;
if (ehci->async_count)
scan_async(ehci);
if (ehci->next_uframe != -1)
scan_periodic (ehci);
- ehci->scanning = 0;
+ if (ehci->need_rescan)
+ goto rescan;
+ ehci->scanning = false;
/* the IO watchdog guards against hardware or driver bugs that
* misplace IRQs, and should let us run completely without IRQs.
--
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