All of lore.kernel.org
 help / color / mirror / Atom feed
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 v6 2/2] spi-atmel: support inter-word delay
Date: Wed, 30 Jan 2019 09:40:05 +0100	[thread overview]
Message-ID: <20190130084005.18649-3-jonas@norrbonn.se> (raw)
In-Reply-To: <20190130084005.18649-1-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>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
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..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) {
-- 
2.19.1


WARNING: multiple messages have this Message-ID (diff)
From: Jonas Bonn <jonas@norrbonn.se>
To: linux-kernel@vger.kernel.org
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>,
	Jonas Bonn <jonas@norrbonn.se>,
	Ludovic Desroches <ludovic.desroches@microchip.com>,
	Mark Brown <broonie@kernel.org>,
	linux-spi@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: [PATCH v6 2/2] spi-atmel: support inter-word delay
Date: Wed, 30 Jan 2019 09:40:05 +0100	[thread overview]
Message-ID: <20190130084005.18649-3-jonas@norrbonn.se> (raw)
In-Reply-To: <20190130084005.18649-1-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>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
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..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) {
-- 
2.19.1


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  parent reply	other threads:[~2019-01-30  8:40 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-30  8:40 [PATCH v6 0/2] spi: support inter-word delays Jonas Bonn
2019-01-30  8:40 ` [PATCH v6 1/2] spi: support inter-word delay requirement for devices Jonas Bonn
2019-01-30 23:02   ` Applied "spi: support inter-word delay requirement for devices" to the spi tree Mark Brown
2019-01-30 23:02     ` Mark Brown
2019-01-30 23:02     ` Mark Brown
2019-01-30  8:40 ` Jonas Bonn [this message]
2019-01-30  8:40   ` [PATCH v6 2/2] spi-atmel: support inter-word delay Jonas Bonn
2019-01-30 23:02   ` Applied "spi-atmel: support inter-word delay" to the spi tree Mark Brown
2019-01-30 23:02     ` Mark Brown
2019-01-30 23:02     ` Mark Brown

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190130084005.18649-3-jonas@norrbonn.se \
    --to=jonas@norrbonn.se \
    --cc=alexandre.belloni@bootlin.com \
    --cc=broonie@kernel.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-spi@vger.kernel.org \
    --cc=ludovic.desroches@microchip.com \
    --cc=nicolas.ferre@microchip.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.