linux-kernel - Applied "spi-atmel: support inter-word delay" to the spi tree

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Date:   Wed, 30 Jan 2019 23:02:47 +0000 (GMT)
From:   Mark Brown <broonie@...nel.org>
To:     Jonas Bonn <jonas@...rbonn.se>
Cc:     Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Mark Brown <broonie@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-spi@...r.kernel.org
Subject: Applied "spi-atmel: support inter-word delay" to the spi tree

The patch

   spi-atmel: support inter-word delay

has been applied to the spi tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From 473a78a7bbeb7c77b81b596095f59ce4fbbd49dc Mon Sep 17 00:00:00 2001
From: Jonas Bonn <jonas@...rbonn.se>
Date: Wed, 30 Jan 2019 09:40:05 +0100
Subject: [PATCH] spi-atmel: support inter-word delay

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@...rbonn.se>
Acked-by: Nicolas Ferre <nicolas.ferre@...rochip.com>
CC: Nicolas Ferre <nicolas.ferre@...rochip.com>
CC: Mark Brown <broonie@...nel.org>
CC: Alexandre Belloni <alexandre.belloni@...tlin.com>
CC: Ludovic Desroches <ludovic.desroches@...rochip.com>
CC: linux-spi@...r.kernel.org
CC: linux-arm-kernel@...ts.infradead.org
Signed-off-by: Mark Brown <broonie@...nel.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..4954f0ab1606 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_usecs) >> 5);
 
 	asd = spi->controller_state;
 	if (!asd) {
-- 
2.20.1