diff mbox

spi: bitbang: only toggle bitchanges

Message ID 1427810089-14866-1-git-send-email-m.grzeschik@pengutronix.de (mailing list archive)
State New, archived
Headers show

Commit Message

Michael Grzeschik March 31, 2015, 1:54 p.m. UTC 
The current implementation of bitbang_txrx_be_cpha0 and
bitbang_txrx_be_cpha1 always call setmosi. That runs into several
unnecessary calls into the gpiolib when the level of the GPIO actually
has not to be changed.

This patch changes the routines to remember the last GPIO level
and only calls setmosi if an change has to be made. This
way it improves the transfer throughput.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
---
 drivers/spi/spi-bitbang-txrx.h | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

Comments

Mark Brown March 31, 2015, 2:13 p.m. UTC | #1 
On Tue, Mar 31, 2015 at 03:54:49PM +0200, Michael Grzeschik wrote:

>  		if ((flags & SPI_MASTER_NO_TX) == 0)
> -			setmosi(spi, word & (1 << 31));
> +			if ((word & (1 << 31)) != oldbit) {
> +				setmosi(spi, word & (1 << 31));
> +				oldbit = word & (1 << 31);
> +			}
>  		spidelay(nsecs);	/* T(setup) */

This change is fine but for legibility can you please add braces around
the outer if as well?
diff mbox

Patch

diff --git a/drivers/spi/spi-bitbang-txrx.h b/drivers/spi/spi-bitbang-txrx.h
index c616e41..62bdf62 100644
--- a/drivers/spi/spi-bitbang-txrx.h
+++ b/drivers/spi/spi-bitbang-txrx.h
@@ -49,12 +49,16 @@  bitbang_txrx_be_cpha0(struct spi_device *spi,
 {
 	/* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */
 
+	bool oldbit = !(word & 1);
 	/* clock starts at inactive polarity */
 	for (word <<= (32 - bits); likely(bits); bits--) {
 
 		/* setup MSB (to slave) on trailing edge */
 		if ((flags & SPI_MASTER_NO_TX) == 0)
-			setmosi(spi, word & (1 << 31));
+			if ((word & (1 << 31)) != oldbit) {
+				setmosi(spi, word & (1 << 31));
+				oldbit = word & (1 << 31);
+			}
 		spidelay(nsecs);	/* T(setup) */
 
 		setsck(spi, !cpol);
@@ -76,13 +80,17 @@  bitbang_txrx_be_cpha1(struct spi_device *spi,
 {
 	/* if (cpol == 0) this is SPI_MODE_1; else this is SPI_MODE_3 */
 
+	bool oldbit = !(word & (1 << 31));
 	/* clock starts at inactive polarity */
 	for (word <<= (32 - bits); likely(bits); bits--) {
 
 		/* setup MSB (to slave) on leading edge */
 		setsck(spi, !cpol);
 		if ((flags & SPI_MASTER_NO_TX) == 0)
-			setmosi(spi, word & (1 << 31));
+			if ((word & (1 << 31)) != oldbit) {
+				setmosi(spi, word & (1 << 31));
+				oldbit = word & (1 << 31);
+			}
 		spidelay(nsecs); /* T(setup) */
 
 		setsck(spi, cpol);