usb_storage: fix ehci driver max transfer size

The commit 5dd95cf93dfffa1d19a1928990852aac9f55b9d9 'usb_storage:
Fix EHCI "out of buffer pointers" with CD-ROM' introduce a bug in
usb_storage as it wrongly assumes that every transfer can use
4096 bytes per qt_buffer. This is wrong if the start address of
the data is not page aligned to 4096 bytes and leads to 'EHCI
timed out on TD' messages because of 'out of buffer pointers'
in ehci_td_buffer function.

The bug appears during load of a fragmented file and
read from or write to an unaligned memory address.

Cc: Marek Vasut <marex@denx.de>
Signed-off-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>

common/usb_storage.c

@@ -150,12 +150,17 @@ struct us_data {
 	unsigned int	irqpipe;	 	/* pipe for release_irq */
 	unsigned char	irqmaxp;		/* max packed for irq Pipe */
 	unsigned char	irqinterval;		/* Intervall for IRQ Pipe */
-	unsigned long	max_xfer_blk;		/* Max blocks per xfer */
 	ccb		*srb;			/* current srb */
 	trans_reset	transport_reset;	/* reset routine */
 	trans_cmnd	transport;		/* transport routine */
 };
 
+/*
+ * The U-Boot EHCI driver cannot handle more than 5 page aligned buffers
+ * of 4096 bytes in a transfer without running itself out of qt_buffers
+ */
+#define USB_MAX_XFER_BLK(start, blksz)	(((4096 * 5) - (start % 4096)) / blksz)
+
 static struct us_data usb_stor[USB_MAX_STOR_DEV];
 
 
@@ -1041,7 +1046,7 @@ static void usb_bin_fixup(struct usb_device_descriptor descriptor,
 unsigned long usb_stor_read(int device, unsigned long blknr,
 			    unsigned long blkcnt, void *buffer)
 {
-	unsigned long start, blks, buf_addr;
+	unsigned long start, blks, buf_addr, max_xfer_blk;
 	unsigned short smallblks;
 	struct usb_device *dev;
 	struct us_data *ss;
@@ -1083,12 +1088,14 @@ unsigned long usb_stor_read(int device, unsigned long blknr,
 		/* XXX need some comment here */
 		retry = 2;
 		srb->pdata = (unsigned char *)buf_addr;
-		if (blks > ss->max_xfer_blk)
-			smallblks = ss->max_xfer_blk;
+		max_xfer_blk = USB_MAX_XFER_BLK(buf_addr,
+						usb_dev_desc[device].blksz);
+		if (blks > max_xfer_blk)
+			smallblks = (unsigned short) max_xfer_blk;
 		else
 			smallblks = (unsigned short) blks;
 retry_it:
-		if (smallblks == ss->max_xfer_blk)
+		if (smallblks == max_xfer_blk)
 			usb_show_progress();
 		srb->datalen = usb_dev_desc[device].blksz * smallblks;
 		srb->pdata = (unsigned char *)buf_addr;
@@ -1109,7 +1116,7 @@ retry_it:
 			start, smallblks, buf_addr);
 
 	usb_disable_asynch(0); /* asynch transfer allowed */
-	if (blkcnt >= ss->max_xfer_blk)
+	if (blkcnt >= max_xfer_blk)
 		debug("\n");
 	return blkcnt;
 }
@@ -1117,7 +1124,7 @@ retry_it:
 unsigned long usb_stor_write(int device, unsigned long blknr,
 				unsigned long blkcnt, const void *buffer)
 {
-	unsigned long start, blks, buf_addr;
+	unsigned long start, blks, buf_addr, max_xfer_blk;
 	unsigned short smallblks;
 	struct usb_device *dev;
 	struct us_data *ss;
@@ -1162,12 +1169,14 @@ unsigned long usb_stor_write(int device, unsigned long blknr,
 		 */
 		retry = 2;
 		srb->pdata = (unsigned char *)buf_addr;
-		if (blks > ss->max_xfer_blk)
-			smallblks = ss->max_xfer_blk;
+		max_xfer_blk = USB_MAX_XFER_BLK(buf_addr,
+						usb_dev_desc[device].blksz);
+		if (blks > max_xfer_blk)
+			smallblks = (unsigned short) max_xfer_blk;
 		else
 			smallblks = (unsigned short) blks;
 retry_it:
-		if (smallblks == ss->max_xfer_blk)
+		if (smallblks == max_xfer_blk)
 			usb_show_progress();
 		srb->datalen = usb_dev_desc[device].blksz * smallblks;
 		srb->pdata = (unsigned char *)buf_addr;
@@ -1188,7 +1197,7 @@ retry_it:
 			start, smallblks, buf_addr);
 
 	usb_disable_asynch(0); /* asynch transfer allowed */
-	if (blkcnt >= ss->max_xfer_blk)
+	if (blkcnt >= max_xfer_blk)
 		debug("\n");
 	return blkcnt;
 
@@ -1415,12 +1424,6 @@ int usb_stor_get_info(struct usb_device *dev, struct us_data *ss,
 	USB_STOR_PRINTF(" address %d\n", dev_desc->target);
 	USB_STOR_PRINTF("partype: %d\n", dev_desc->part_type);
 
-	/*
-	 * The U-Boot EHCI driver cannot handle more than 4096 * 5 bytes in a
-	 * transfer without running itself out of qt_buffers.
-	 */
-	ss->max_xfer_blk = (4096 * 5) / dev_desc->blksz;
-
 	init_part(dev_desc);
 
 	USB_STOR_PRINTF("partype: %d\n", dev_desc->part_type);