From: Jonas Bonn <jonas@norrbonn.se>
To: linux-kernel@vger.kernel.org
Cc: Jonas Bonn <jonas@norrbonn.se>,
Nicolas Ferre <nicolas.ferre@microchip.com>,
Mark Brown <broonie@kernel.org>,
Alexandre Belloni <alexandre.belloni@bootlin.com>,
Ludovic Desroches <ludovic.desroches@microchip.com>,
linux-spi@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: [PATCH v5 2/2] spi-atmel: support inter-word delay
Date: Tue, 29 Jan 2019 21:55:02 +0100 [thread overview]
Message-ID: <20190129205502.7741-3-jonas@norrbonn.se> (raw)
In-Reply-To: <20190129205502.7741-1-jonas@norrbonn.se>
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
next prev parent reply other threads:[~2019-01-29 20:55 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-29 20:55 [PATCH v5 0/2] spi: support inter-word delays Jonas Bonn
2019-01-29 20:55 ` [PATCH v5 1/2] spi: support inter-word delay requirement for devices Jonas Bonn
2019-01-30 7:35 ` Geert Uytterhoeven
2019-01-30 8:10 ` Jonas Bonn
2019-01-30 8:15 ` Geert Uytterhoeven
2019-01-31 12:46 ` Mark Brown
2019-01-29 20:55 ` Jonas Bonn [this message]
2019-01-30 8:15 ` [PATCH v5 2/2] spi-atmel: support inter-word delay Nicolas.Ferre
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