[14/18] dmaengine/amba-pl08x: Choose peripheral bus as master bus
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Message ID c1cb9cd2abc64b4efdc3648896324a1821fdba3e.1311936524.git.viresh.kumar@st.com
State New, archived
Headers show

Commit Message

Viresh KUMAR July 29, 2011, 10:49 a.m. UTC
When we have DMA transfers between peripheral and memory, then we shouldn't
reduce width of peripheral at all, as that may be a strict requirement. But we
can always reduce width of memory access, with some compromise in performance.
Thus, we must select peripheral as master and not memory.

Also this rearranges code to make it shorter.

Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
---
 drivers/dma/amba-pl08x.c |   22 ++++++----------------
 1 files changed, 6 insertions(+), 16 deletions(-)

Comments

Linus Walleij July 31, 2011, 12:36 a.m. UTC | #1
2011/7/29 Viresh Kumar <viresh.kumar@st.com>:

> When we have DMA transfers between peripheral and memory, then we shouldn't
> reduce width of peripheral at all, as that may be a strict requirement. But we
> can always reduce width of memory access, with some compromise in performance.
> Thus, we must select peripheral as master and not memory.
>
> Also this rearranges code to make it shorter.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@st.com>

Looks correct to me!
Acked-by: Linus Walleij <linus.walleij@linaro.org>

Thanks,
Linus Walleij

Patch
diff mbox

diff --git a/drivers/dma/amba-pl08x.c b/drivers/dma/amba-pl08x.c
index 44f317a..6b0ca26 100644
--- a/drivers/dma/amba-pl08x.c
+++ b/drivers/dma/amba-pl08x.c
@@ -492,34 +492,24 @@  struct pl08x_lli_build_data {
 /*
  * Autoselect a master bus to use for the transfer
  * - prefers the destination bus if both available
- * - if fixed address on one bus the other will be chosen
+ * - prefers bus with fixed address (i.e. peripheral)
  */
 static void pl08x_choose_master_bus(struct pl08x_lli_build_data *bd,
 	struct pl08x_bus_data **mbus, struct pl08x_bus_data **sbus, u32 cctl)
 {
 	if (!(cctl & PL080_CONTROL_DST_INCR)) {
-		*mbus = &bd->srcbus;
-		*sbus = &bd->dstbus;
-	} else if (!(cctl & PL080_CONTROL_SRC_INCR)) {
 		*mbus = &bd->dstbus;
 		*sbus = &bd->srcbus;
+	} else if (!(cctl & PL080_CONTROL_SRC_INCR)) {
+		*mbus = &bd->srcbus;
+		*sbus = &bd->dstbus;
 	} else {
-		if (bd->dstbus.buswidth == 4) {
-			*mbus = &bd->dstbus;
-			*sbus = &bd->srcbus;
-		} else if (bd->srcbus.buswidth == 4) {
-			*mbus = &bd->srcbus;
-			*sbus = &bd->dstbus;
-		} else if (bd->dstbus.buswidth == 2) {
+		if (bd->dstbus.buswidth >= bd->srcbus.buswidth) {
 			*mbus = &bd->dstbus;
 			*sbus = &bd->srcbus;
-		} else if (bd->srcbus.buswidth == 2) {
+		} else {
 			*mbus = &bd->srcbus;
 			*sbus = &bd->dstbus;
-		} else {
-			/* bd->srcbus.buswidth == 1 */
-			*mbus = &bd->dstbus;
-			*sbus = &bd->srcbus;
 		}
 	}
 }