[PATCH 2/6] spi: spi-fsl-dspi: Fix little endian access to PUSHR CMD and TXDATA

[Vladimir Oltean <olteanv@gmail.com>]

From: Vladimir Oltean <vladimir.oltean@nxp.com>

In XSPI mode, the 32-bit PUSHR register can be written to separately:
the higher 16 bits are for commands and the lower 16 bits are for data.

This has nicely been hacked around, by defining a second regmap with a
width of 16 bits, and effectively splitting a 32-bit register into 2
16-bit ones, from the perspective of this regmap_pushr.

The problem is the assumption about the controller's endianness. If the
controller is little endian (such as anything post-LS1046A), then the
first 2 bytes, in the order imposed by memory layout, will actually hold
the TXDATA, and the last 2 bytes will hold the CMD.

So take the controller's endianness into account when performing split
writes to PUSHR. The obvious and simple solution would have been to call
regmap_get_val_endian(), but that is an internal regmap function and we
don't want to change regmap just for this. Therefore, we define the
offsets per-instantiation, in the devtype_data structure. This means
that we have to know from the driver which controllers are big- and
which are little-endian (which is fine, we do, but it makes the device
tree binding itself a little redundant except for regmap_config).

This patch does not apply cleanly to stable trees, and a punctual fix to
the commit cannot be provided given this constraint of lack of access to
regmap_get_val_endian(). The per-SoC devtype_data structures (and
therefore the premises to fix this bug) have been introduced only a few
commits ago, in commit d35054010b57 ("spi: spi-fsl-dspi: Use specific
compatible strings for all SoC instantiations")

Fixes: 58ba07ec79e6 ("spi: spi-fsl-dspi: Add support for XSPI mode registers")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/spi/spi-fsl-dspi.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/drivers/spi/spi-fsl-dspi.c b/drivers/spi/spi-fsl-dspi.c
index 0ce26c1cbf62..a8e56abe20ac 100644
--- a/drivers/spi/spi-fsl-dspi.c
+++ b/drivers/spi/spi-fsl-dspi.c
@@ -103,10 +103,6 @@
 #define SPI_FRAME_BITS(bits)		SPI_CTAR_FMSZ((bits) - 1)
 #define SPI_FRAME_EBITS(bits)		SPI_CTARE_FMSZE(((bits) - 1) >> 4)
 
-/* Register offsets for regmap_pushr */
-#define PUSHR_CMD			0x0
-#define PUSHR_TX			0x2
-
 #define DMA_COMPLETION_TIMEOUT		msecs_to_jiffies(3000)
 
 struct chip_data {
@@ -124,6 +120,12 @@ struct fsl_dspi_devtype_data {
 	u8			max_clock_factor;
 	int			fifo_size;
 	int			dma_bufsize;
+	/*
+	 * Offsets for CMD and TXDATA within SPI_PUSHR when accessed
+	 * individually (in XSPI mode)
+	 */
+	int			pushr_cmd;
+	int			pushr_tx;
 };
 
 enum {
@@ -150,42 +152,56 @@ static const struct fsl_dspi_devtype_data devtype_data[] = {
 		.trans_mode		= DSPI_XSPI_MODE,
 		.max_clock_factor	= 8,
 		.fifo_size		= 4,
+		.pushr_cmd		= 0,
+		.pushr_tx		= 2,
 	},
 	[LS1012A] = {
 		/* Has A-011218 DMA erratum */
 		.trans_mode		= DSPI_XSPI_MODE,
 		.max_clock_factor	= 8,
 		.fifo_size		= 16,
+		.pushr_cmd		= 0,
+		.pushr_tx		= 2,
 	},
 	[LS1043A] = {
 		/* Has A-011218 DMA erratum */
 		.trans_mode		= DSPI_XSPI_MODE,
 		.max_clock_factor	= 8,
 		.fifo_size		= 16,
+		.pushr_cmd		= 0,
+		.pushr_tx		= 2,
 	},
 	[LS1046A] = {
 		/* Has A-011218 DMA erratum */
 		.trans_mode		= DSPI_XSPI_MODE,
 		.max_clock_factor	= 8,
 		.fifo_size		= 16,
+		.pushr_cmd		= 0,
+		.pushr_tx		= 2,
 	},
 	[LS2080A] = {
 		.trans_mode		= DSPI_DMA_MODE,
 		.dma_bufsize		= 8,
 		.max_clock_factor	= 8,
 		.fifo_size		= 4,
+		.pushr_cmd		= 2,
+		.pushr_tx		= 0,
 	},
 	[LS2085A] = {
 		.trans_mode		= DSPI_DMA_MODE,
 		.dma_bufsize		= 8,
 		.max_clock_factor	= 8,
 		.fifo_size		= 4,
+		.pushr_cmd		= 2,
+		.pushr_tx		= 0,
 	},
 	[LX2160A] = {
 		.trans_mode		= DSPI_DMA_MODE,
 		.dma_bufsize		= 8,
 		.max_clock_factor	= 8,
 		.fifo_size		= 4,
+		.pushr_cmd		= 2,
+		.pushr_tx		= 0,
 	},
 	[MCF5441X] = {
 		.trans_mode		= DSPI_EOQ_MODE,
@@ -670,12 +686,12 @@ static void dspi_pushr_cmd_write(struct fsl_dspi *dspi, u16 cmd)
 	 */
 	if (dspi->len > dspi->oper_word_size)
 		cmd |= SPI_PUSHR_CMD_CONT;
-	regmap_write(dspi->regmap_pushr, PUSHR_CMD, cmd);
+	regmap_write(dspi->regmap_pushr, dspi->devtype_data->pushr_cmd, cmd);
 }
 
 static void dspi_pushr_txdata_write(struct fsl_dspi *dspi, u16 txdata)
 {
-	regmap_write(dspi->regmap_pushr, PUSHR_TX, txdata);
+	regmap_write(dspi->regmap_pushr, dspi->devtype_data->pushr_tx, txdata);
 }
 
 static void dspi_xspi_write(struct fsl_dspi *dspi, int cnt, bool eoq)
-- 
2.17.1