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

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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>
This commit is contained in:
Ming Lei
2011-08-30 16:03:13 +00:00
committed by Benoit Goby
parent 7013f49763
commit 95cf7a199c
2 changed files with 35 additions and 0 deletions
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18
drivers/usb/host/ehci-q.c
View File

@@ -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);
}
}

17
drivers/usb/host/ehci.h
View File

@@ -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