On 25/01/2019 12:44, Jonas Bonn wrote:
If the SPI slave requires an inter-word delay, configure the DLYBCT
register accordingly.
Tested on a SAMA5D2 board (derived from SAMA5D2-Xplained reference
board).
Signed-off-by: Jonas Bonn <jonas@xxxxxxxxxxx>
CC: Nicolas Ferre <nicolas.ferre@xxxxxxxxxxxxx>
CC: Mark Brown <broonie@xxxxxxxxxx>
CC: Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx>
CC: Ludovic Desroches <ludovic.desroches@xxxxxxxxxxxxx>
CC: linux-spi@xxxxxxxxxxxxxxx
CC: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
---
drivers/spi/spi-atmel.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff --git a/drivers/spi/spi-atmel.c b/drivers/spi/spi-atmel.c
index 74fddcd3282b..88ff3fef56e9 100644
--- a/drivers/spi/spi-atmel.c
+++ b/drivers/spi/spi-atmel.c
@@ -1209,13 +1209,14 @@ static int atmel_spi_setup(struct spi_device *spi)
csr |= SPI_BIT(CSAAT);
/* DLYBS is mostly irrelevant since we manage chipselect using GPIOs.
- *
- * DLYBCT would add delays between words, slowing down transfers.
- * It could potentially be useful to cope with DMA bottlenecks, but
- * in those cases it's probably best to just use a lower bitrate.
*/
csr |= SPI_BF(DLYBS, 0);
- csr |= SPI_BF(DLYBCT, 0);
+
+ /* DLYBCT adds delays between words. This is useful for slow devices
+ * that need a bit of time to setup the next transfer.
+ */
+ csr |= SPI_BF(DLYBCT,
+ clamp_t(u8, (as->spi_clk/1000000*spi->word_delay)>>5, 1, 255));
Ah... this is stupid. The clamping here _always_ introduces a delay,
which is not what we want... will resubmit this.
/Jonas
/* chipselect must have been muxed as GPIO (e.g. in board setup) */
npcs_pin = (unsigned long)spi->controller_data;
