* [PATCH v5 2/2] spi-atmel: support inter-word delay
[not found] <20190129205502.7741-1-jonas@norrbonn.se>
@ 2019-01-29 20:55 ` Jonas Bonn
2019-01-30 8:15 ` Nicolas.Ferre
0 siblings, 1 reply; 2+ messages in thread
From: Jonas Bonn @ 2019-01-29 20:55 UTC (permalink / raw)
To: linux-kernel
Cc: Alexandre Belloni, Jonas Bonn, Ludovic Desroches, Mark Brown,
linux-spi, linux-arm-kernel
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@norrbonn.se>
CC: Nicolas Ferre <nicolas.ferre@microchip.com>
CC: Mark Brown <broonie@kernel.org>
CC: Alexandre Belloni <alexandre.belloni@bootlin.com>
CC: Ludovic Desroches <ludovic.desroches@microchip.com>
CC: linux-spi@vger.kernel.org
CC: linux-arm-kernel@lists.infradead.org
---
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 f53f0c5e63da..57cc7110f9e8 100644
--- a/drivers/spi/spi-atmel.c
+++ b/drivers/spi/spi-atmel.c
@@ -1201,13 +1201,14 @@ 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,
+ (as->spi_clk / 1000000 * spi->word_delay_us) >> 5);
asd = spi->controller_state;
if (!asd) {
--
2.19.1
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^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v5 2/2] spi-atmel: support inter-word delay
2019-01-29 20:55 ` [PATCH v5 2/2] spi-atmel: support inter-word delay Jonas Bonn
@ 2019-01-30 8:15 ` Nicolas.Ferre
0 siblings, 0 replies; 2+ messages in thread
From: Nicolas.Ferre @ 2019-01-30 8:15 UTC (permalink / raw)
To: jonas, linux-kernel, broonie
Cc: alexandre.belloni, Tudor.Ambarus, Ludovic.Desroches,
linux-arm-kernel, linux-spi
On 29/01/2019 at 21:55, 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@norrbonn.se>
> CC: Nicolas Ferre <nicolas.ferre@microchip.com>
> CC: Mark Brown <broonie@kernel.org>
> CC: Alexandre Belloni <alexandre.belloni@bootlin.com>
> CC: Ludovic Desroches <ludovic.desroches@microchip.com>
> CC: linux-spi@vger.kernel.org
> CC: linux-arm-kernel@lists.infradead.org
> ---
> 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 f53f0c5e63da..57cc7110f9e8 100644
> --- a/drivers/spi/spi-atmel.c
> +++ b/drivers/spi/spi-atmel.c
> @@ -1201,13 +1201,14 @@ 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,
> + (as->spi_clk / 1000000 * spi->word_delay_us) >> 5);
Looks good to me:
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
> asd = spi->controller_state;
> if (!asd) {
>
--
Nicolas Ferre
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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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2019-01-29 20:55 ` [PATCH v5 2/2] spi-atmel: support inter-word delay Jonas Bonn
2019-01-30 8:15 ` Nicolas.Ferre
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