linux-kernel - [LINUX RFC v3 1/4] spi: addng support for data stripe feature in core

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Message-ID: <1450098585-3129-2-git-send-email-ranjit.waghmode@xilinx.com>
Date:	Mon, 14 Dec 2015 18:39:42 +0530
From:	Ranjit Waghmode <ranjit.waghmode@...inx.com>
To:	<broonie@...nel.org>, <dwmw2@...radead.org>,
	<computersforpeace@...il.com>, <swarren@...dia.com>,
	<geert+renesas@...der.be>, <afd@...com>, <jic23@...nel.org>,
	<marex@...x.de>, <jteki@...nedev.com>, <zajec5@...il.com>,
	<juhosg@...nwrt.org>, <mika.westerberg@...ux.intel.com>,
	<sean.nyekjaer@...vas.dk>, <beanhuo@...ron.com>,
	<furquan@...gle.com>, <michal.simek@...inx.com>,
	<soren.brinkmann@...inx.com>
CC:	<linux-spi@...r.kernel.org>, <linux-mtd@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <harinik@...inx.com>,
	<punnaia@...inx.com>, <ran27jit@...il.com>,
	"Ranjit Waghmode" <ranjit.waghmode@...inx.com>
Subject: [LINUX RFC v3 1/4] spi: addng support for data stripe feature in core

This patch enables data stripe feature in spi core. This feature is
required to support dual parallel mode of ZynqMP GQSPI controller.

To achieve the same an API SPI_MASTER_DATA_STRIPE is added.
With data stripe enabled,
  - even bytes i.e. 0, 2, 4,... are transmitted on lower data bus
  - odd bytes i.e. 1, 3, 5,.. are transmitted on upper data bus.

To support data stripe; need to  assert both chip selects once.
This is achieved throught API SPI_MASTER_BOTH_CS.

Signed-off-by: Ranjit Waghmode <ranjit.waghmode@...inx.com>

---
V3 Changes:
	- Updated comments for newly added APIs.
	- Changed patch description for ease of understanding
V2 Changes:
	- Added error handling condition for newly added features
---

 drivers/spi/spi.c       |  8 ++++++++
 include/linux/spi/spi.h | 11 +++++++++++
 2 files changed, 19 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 2b0a8ec..930dac3 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -2106,6 +2106,14 @@ static int __spi_validate(struct spi_device *spi, struct spi_message *message)
 	if (list_empty(&message->transfers))
 		return -EINVAL;

+	/*
+	 * Data stripe option is selected if and only if when
+	 * two chips are enabled
+	 */
+	if ((master->flags & SPI_MASTER_DATA_STRIPE)
+		&& !(master->flags & SPI_MASTER_BOTH_CS))
+			return -EINVAL;
+
 	/* Half-duplex links include original MicroWire, and ones with
 	 * only one data pin like SPI_3WIRE (switches direction) or where
 	 * either MOSI or MISO is missing.  They can also be caused by
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index cce80e6..e83b667 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -424,6 +424,17 @@ struct spi_master {
 #define SPI_MASTER_NO_TX	BIT(2)		/* can't do buffer write */
 #define SPI_MASTER_MUST_RX      BIT(3)		/* requires rx */
 #define SPI_MASTER_MUST_TX      BIT(4)		/* requires tx */
+	/* Controller may support data stripe feature when more than one
+	 * chips are present.
+	 * Setting data stripe will send data in following manner:
+	 * -> even bytes i.e. 0, 2, 4,... are transmitted on lower data bus
+	 * -> odd bytes i.e. 1, 3, 5,.. are transmitted on upper data bus
+	 */
+#define SPI_MASTER_DATA_STRIPE	BIT(7)		/* support data stripe */
+	/* Controller may support asserting more than one chip select at once.
+	 * This flag will enable that feature.
+	 */
+#define SPI_MASTER_BOTH_CS	BIT(8)		/* assert both chip selects */

 	/* lock and mutex for SPI bus locking */
 	spinlock_t		bus_lock_spinlock;
--
2.1.2

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