usb: musb: host: Issue a memory barrier before starting DMA
This patch fixes the issue which was observed while transfering
a large file ( > 20MB) over USB (OMAP MUSB controller acts as USB host)
to an attached USB thumb drive.
It was found that CDB field of CBW packet was set to 0x0. This was
due to missing a barrier before DMA engine starts transfer.
This buffer is allocated using dma_alloc_coherent which gives
non-cacheble but bufferable memory and hence needed a write
memory barrier to flush the write buffer.
More info on this thread is here:
http://www.spinics.net/lists/linux-omap/msg33987.html
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Maulik Mankad <x0082077@ti.com>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
diff --git a/drivers/usb/musb/musb_host.c b/drivers/usb/musb/musb_host.c
index 877d20b..9e65c47 100644
--- a/drivers/usb/musb/musb_host.c
+++ b/drivers/usb/musb/musb_host.c
@@ -660,6 +660,12 @@
qh->segsize = length;
+ /*
+ * Ensure the data reaches to main memory before starting
+ * DMA transfer
+ */
+ wmb();
+
if (!dma->channel_program(channel, pkt_size, mode,
urb->transfer_dma + offset, length)) {
dma->channel_release(channel);