mpsse: check available buffer space even for discarded data scans

When there's no data to scan in or out, we still use the clock data out
command and fill the buffer with zeroes, so make sure the buffer is
checked for available space.

Change-Id: Ia6005c40c81f7fdb89379f1b5023fe383184d210
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/793
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>

src/jtag/drivers/mpsse.c

@@ -443,8 +443,8 @@ int mpsse_clock_data(struct mpsse_ctx *ctx, const uint8_t *out, unsigned out_off
 
 	while (length > 0) {
 		/* Guarantee buffer space enough for a minimum size transfer */
-		if (buffer_write_space(ctx) + (length < 8) < (out ? 4 : 3)
-		    || (in && buffer_read_space(ctx) < 1))
+		if (buffer_write_space(ctx) + (length < 8) < (out || (!out && !in) ? 4 : 3)
+				|| (in && buffer_read_space(ctx) < 1))
 			retval = mpsse_flush(ctx);
 
 		if (length < 8) {
@@ -465,8 +465,8 @@ int mpsse_clock_data(struct mpsse_ctx *ctx, const uint8_t *out, unsigned out_off
 			if (this_bytes > 65536)
 				this_bytes = 65536;
 			/* Buffer space limit. We already made sure there's space for the minimum
-			 *transfer. */
-			if (out && this_bytes + 3 > buffer_write_space(ctx))
+			 * transfer. */
+			if ((out || (!out && !in)) && this_bytes + 3 > buffer_write_space(ctx))
 				this_bytes = buffer_write_space(ctx) - 3;
 			if (in && this_bytes > buffer_read_space(ctx))
 				this_bytes = buffer_read_space(ctx);