usb: ehci: make HC see up-to-date qh/qtd descriptor ASAP

This patch introduces the helper of ehci_sync_mem to flush
qtd/qh into memory immediately on some ARM, so that HC can
see the up-to-date qtd/qh descriptor asap.

This patch fixs one performance bug on ARM Cortex A9 dual core
platform, which has been reported on quite a few ARM machines
(OMAP4, Tegra 2, snowball...), see details from link of
https://bugs.launchpad.net/bugs/709245.

The patch has been tested ok on OMAP4 panda A1 board, and the
performance of 'dd' over usb mass storage can be increased from
4~5MB/sec to 14~16MB/sec after applying this patch.

Change-Id: I7994c58a1001c7f46f13e09420328a3916bbfcef
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>

diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index 0917e3a32465064903dd884cc2c258baadadc0f2..271987952e338e2f60ea14f7d21c88a81f75981a 100644 (file)
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -995,6 +995,12 @@ static void qh_link_async (struct ehci_hcd *ehci, struct ehci_qh *qh)
        head->qh_next.qh = qh;
        head->hw->hw_next = dma;
 
+       /*
+        * flush qh descriptor into memory immediately,
+        * see comments in qh_append_tds.
+        * */
+       ehci_sync_mem();
+
        qh_get(qh);
        qh->xacterrs = 0;
        qh->qh_state = QH_STATE_LINKED;
@@ -1082,6 +1088,18 @@ static struct ehci_qh *qh_append_tds (
                        wmb ();
                        dummy->hw_token = token;
 
+                       /*
+                        * Writing to dma coherent buffer on ARM may
+                        * be delayed to reach memory, so HC may not see
+                        * hw_token of dummy qtd in time, which can cause
+                        * the qtd transaction to be executed very late,
+                        * and degrade performance a lot. ehci_sync_mem
+                        * is added to flush 'token' immediatelly into
+                        * memory, so that ehci can execute the transaction
+                        * ASAP.
+                        * */
+                       ehci_sync_mem();
+
                        urb->hcpriv = qh_get (qh);
                }
        }

diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
index 989e0a8e01f59cc026af5563d5acc15e144208f4..9706c2b64a947b7fee05df62ced3bfb8594082ce 100644 (file)
--- a/drivers/usb/host/ehci.h
+++ b/drivers/usb/host/ehci.h
@@ -736,6 +736,23 @@ static inline u32 hc32_to_cpup (const struct ehci_hcd *ehci, const __hc32 *x)
 
 #endif
 
+/*
+ * Writing to dma coherent memory on ARM may be delayed via L2
+ * writing buffer, so introduce the helper which can flush L2 writing
+ * buffer into memory immediately, especially used to flush ehci
+ * descriptor to memory.
+ * */
+#ifdef CONFIG_ARM_DMA_MEM_BUFFERABLE
+static inline void ehci_sync_mem()
+{
+       mb();
+}
+#else
+static inline void ehci_sync_mem()
+{
+}
+#endif
+
 /*-------------------------------------------------------------------------*/
 
 #ifndef DEBUG