[PATCH v2] spi: bitbang: only toggle bitchanges
From: Jonas Gorski <hidden>
Date: 2015-03-31 18:59:28
Also in:
linux-spi
On Tue, Mar 31, 2015 at 4:35 PM, Michael Grzeschik [off-list ref] wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- v2: added missing braces drivers/spi/spi-bitbang-txrx.h | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-)diff --git a/drivers/spi/spi-bitbang-txrx.h b/drivers/spi/spi-bitbang-txrx.h index c616e41..06b34e5 100644 --- a/drivers/spi/spi-bitbang-txrx.h +++ b/drivers/spi/spi-bitbang-txrx.h@@ -49,12 +49,17 @@ 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);
Is it intentional you check the first bit (word & 1) here? Everywhere else you use (word & 31).
/* 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 ((flags & SPI_MASTER_NO_TX) == 0) {
+ if ((word & (1 << 31)) != oldbit) {You are comparing a bool to an int, and ((word & (1 << 31)) will always be != true (== 1). Your condition needs to be !!(word & (1 << 31)) != oldbit .
quoted hunk ↗ jump to hunk
+ setmosi(spi, word & (1 << 31)); + oldbit = word & (1 << 31); + } + } spidelay(nsecs); /* T(setup) */ setsck(spi, !cpol);@@ -76,13 +81,18 @@ 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 ((flags & SPI_MASTER_NO_TX) == 0) { + if ((word & (1 << 31)) != oldbit) {
Same issue here.
+ setmosi(spi, word & (1 << 31));
+ oldbit = word & (1 << 31);
+ }
+ }
spidelay(nsecs); /* T(setup) */
setsck(spi, cpol);
--Regards Jonas