[PATCH 1/2] usbmon: do dma sync for cpu read if the buffer is not dma coherent

[Xu Yang <xu.yang_2@nxp.com>]

The urb->transfer_dma may not be dma coherent, in this case usb monitor
may get old data. For example, commit "20e1dbf2bbe2 media: uvcvideo:
Use dma_alloc_noncontiguous API" is allocating non-coherent buffer.

To make usbmon result more reliable, this will add a flag
URB_USBMON_NEED_SYNC to indicate that usb monitor need do dma sync
before reading buffer data.

Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
---
 drivers/usb/mon/mon_main.c | 7 +++++++
 include/linux/usb.h        | 1 +
 2 files changed, 8 insertions(+)

diff --git a/drivers/usb/mon/mon_main.c b/drivers/usb/mon/mon_main.c
index af852d53aac6..b9d5c1b46b85 100644
--- a/drivers/usb/mon/mon_main.c
+++ b/drivers/usb/mon/mon_main.c
@@ -14,6 +14,7 @@
 #include <linux/slab.h>
 #include <linux/notifier.h>
 #include <linux/mutex.h>
+#include <linux/dma-mapping.h>
 
 #include "usb_mon.h"
 
@@ -142,6 +143,12 @@ static void mon_complete(struct usb_bus *ubus, struct urb *urb, int status)
 {
 	struct mon_bus *mbus;
 
+	if (urb->transfer_flags & URB_USBMON_NEED_SYNC)
+		dma_sync_single_for_cpu(ubus->sysdev,
+					urb->transfer_dma,
+					urb->transfer_buffer_length,
+					DMA_FROM_DEVICE);
+
 	mbus = ubus->mon_bus;
 	if (mbus != NULL)
 		mon_bus_complete(mbus, urb, status);
diff --git a/include/linux/usb.h b/include/linux/usb.h
index 1b2545b4363b..d31baee4ffa6 100644
--- a/include/linux/usb.h
+++ b/include/linux/usb.h
@@ -1368,6 +1368,7 @@ extern int usb_disabled(void);
 #define URB_ISO_ASAP		0x0002	/* iso-only; use the first unexpired
 					 * slot in the schedule */
 #define URB_NO_TRANSFER_DMA_MAP	0x0004	/* urb->transfer_dma valid on submit */
+#define URB_USBMON_NEED_SYNC	0x0008	/* usb monitor need do dma sync for cpu read */
 #define URB_ZERO_PACKET		0x0040	/* Finish bulk OUT with short packet */
 #define URB_NO_INTERRUPT	0x0080	/* HINT: no non-error interrupt
 					 * needed */
-- 
2.34.1