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SubjectRe: [PATCH v4 2/2] spi-atmel: support inter-word delay
Date
On 29/01/2019 at 09:38, 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 | 18 +++++++++++++-----
> 1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/spi/spi-atmel.c b/drivers/spi/spi-atmel.c
> index 74fddcd3282b..6389a228d2f5 100644
> --- a/drivers/spi/spi-atmel.c
> +++ b/drivers/spi/spi-atmel.c
> @@ -1209,13 +1209,21 @@ 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.
> + */
> + if (spi->word_delay_us) {

Well...

> + csr |= SPI_BF(DLYBCT,
> + clamp_t(u8,
> + (as->spi_clk/1000000*spi->word_delay_us)>>5,
> + 1, 255));

... why not simplifying to:
+ 0, 255));
and remove the test altogether, after all?

> + } else {
> + csr |= SPI_BF(DLYBCT, 0);
> + }
> +
>
> /* chipselect must have been muxed as GPIO (e.g. in board setup) */
> npcs_pin = (unsigned long)spi->controller_data;
>


--
Nicolas Ferre
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