r8152: adjust generic_ocp_write function

Reduce the control transfer if all bytes of first or the last DWORD are
written.

The original method is to split the control transfer into three parts
(the first DWORD, middle continuous data, and the last DWORD). However,
they could be combined if whole bytes of the first DWORD or last DWORD
are written. That is, the first DWORD or the last DWORD could be combined
with the middle continuous data, if the byte_en is 0xff.

Signed-off-by: Hayes Wang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: hayesorz

drivers/net/usb/r8152.c

@@ -1314,16 +1314,24 @@ static int generic_ocp_write(struct r8152 *tp, u16 index, u16 byteen,
 	byteen_end = byteen & BYTE_EN_END_MASK;
 
 	byen = byteen_start | (byteen_start << 4);
-	ret = set_registers(tp, index, type | byen, 4, data);
-	if (ret < 0)
-		goto error1;
 
-	index += 4;
-	data += 4;
-	size -= 4;
+	/* Split the first DWORD if the byte_en is not 0xff */
+	if (byen != BYTE_EN_DWORD) {
+		ret = set_registers(tp, index, type | byen, 4, data);
+		if (ret < 0)
+			goto error1;
 
-	if (size) {
+		index += 4;
+		data += 4;
 		size -= 4;
+	}
+
+	if (size) {
+		byen = byteen_end | (byteen_end >> 4);
+
+		/* Split the last DWORD if the byte_en is not 0xff */
+		if (byen != BYTE_EN_DWORD)
+			size -= 4;
 
 		while (size) {
 			if (size > limit) {
@@ -1350,10 +1358,9 @@ static int generic_ocp_write(struct r8152 *tp, u16 index, u16 byteen,
 			}
 		}
 
-		byen = byteen_end | (byteen_end >> 4);
-		ret = set_registers(tp, index, type | byen, 4, data);
-		if (ret < 0)
-			goto error1;
+		/* Set the last DWORD */
+		if (byen != BYTE_EN_DWORD)
+			ret = set_registers(tp, index, type | byen, 4, data);
 	}
 
 error1: