USB: EHCI: add native scatter-gather support

This patch (as1300) adds native scatter-gather support to ehci-hcd.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 27 insertions, 5 deletions

diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index 139a2cc..a427d3b 100644
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -616,9 +616,11 @@ qh_urb_transaction (
 ) {
 	struct ehci_qtd		*qtd, *qtd_prev;
 	dma_addr_t		buf;
-	int			len, maxpacket;
+	int			len, this_sg_len, maxpacket;
 	int			is_input;
 	u32			token;
+	int			i;
+	struct scatterlist	*sg;
 
 	/*
 	 * URBs map to sequences of QTDs:  one logical transaction
@@ -659,7 +661,20 @@ qh_urb_transaction (
 	/*
 	 * data transfer stage:  buffer setup
 	 */
-	buf = urb->transfer_dma;
+	i = urb->num_sgs;
+	if (len > 0 && i > 0) {
+		sg = urb->sg->sg;
+		buf = sg_dma_address(sg);
+
+		/* urb->transfer_buffer_length may be smaller than the
+		 * size of the scatterlist (or vice versa)
+		 */
+		this_sg_len = min_t(int, sg_dma_len(sg), len);
+	} else {
+		sg = NULL;
+		buf = urb->transfer_dma;
+		this_sg_len = len;
+	}
 
 	if (is_input)
 		token |= (1 /* "in" */ << 8);
@@ -675,7 +690,9 @@ qh_urb_transaction (
 	for (;;) {
 		int this_qtd_len;
 
-		this_qtd_len = qtd_fill(ehci, qtd, buf, len, token, maxpacket);
+		this_qtd_len = qtd_fill(ehci, qtd, buf, this_sg_len, token,
+				maxpacket);
+		this_sg_len -= this_qtd_len;
 		len -= this_qtd_len;
 		buf += this_qtd_len;
 
@@ -691,8 +708,13 @@ qh_urb_transaction (
 		if ((maxpacket & (this_qtd_len + (maxpacket - 1))) == 0)
 			token ^= QTD_TOGGLE;
 
-		if (likely (len <= 0))
-			break;
+		if (likely(this_sg_len <= 0)) {
+			if (--i <= 0 || len <= 0)
+				break;
+			sg = sg_next(sg);
+			buf = sg_dma_address(sg);
+			this_sg_len = min_t(int, sg_dma_len(sg), len);
+		}
 
 		qtd_prev = qtd;
 		qtd = ehci_qtd_alloc (ehci, flags);