[PATCH v3 2/2] spi: dw: Allow interface drivers to limit data I/O to word sizes

Fixes: dd11444327ce ("spi: dw-spi: Convert 16bit accesses to 32bit 
accesses")
Signed-off-by: Michael van der Westhuizen <redacted>
---
Changes in v3:
  - Rename the DT property as requested by Rob Herring.

Changes in v2:
  - Incorporate review feedback from Andy Shevchenko
    - Rework the DT bindings to accept an I/O register width as a
      number of bytes rather than using a boolean spefifying the
      width preference to be 16 bits.
    - Add data register access wrapper functions and use them when
      reading and writing the data register.

 drivers/spi/spi-dw-mmio.c |  3 +++
 drivers/spi/spi-dw.c      |  4 ++--
 drivers/spi/spi-dw.h      | 35 +++++++++++++++++++++++++++++++++++
 3 files changed, 40 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-dw-mmio.c b/drivers/spi/spi-dw-mmio.c
index eb03e12..7edede6 100644
--- a/drivers/spi/spi-dw-mmio.c
+++ b/drivers/spi/spi-dw-mmio.c

@@ -74,6 +74,9 @@ static int dw_spi_mmio_probe(struct platform_device 

*pdev)
 
 	dws->max_freq = clk_get_rate(dwsmmio->clk);
 
+	of_property_read_u32(pdev->dev.of_node, "reg-io-width",
+			     &dws->reg_io_width);
+
 	num_cs = 4;
 
 	if (pdev->dev.of_node)

diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
index 8d67d03..4fbfcdc 100644
--- a/drivers/spi/spi-dw.c
+++ b/drivers/spi/spi-dw.c

@@ -194,7 +194,7 @@ static void dw_writer(struct dw_spi *dws)
 			else
 				txw = *(u16 *)(dws->tx);
 		}
-		dw_writel(dws, DW_SPI_DR, txw);
+		dw_write_io_reg(dws, DW_SPI_DR, txw);
 		dws->tx += dws->n_bytes;
 	}
 }

@@ -205,7 +205,7 @@ static void dw_reader(struct dw_spi *dws)
 	u16 rxw;
 
 	while (max--) {
-		rxw = dw_readl(dws, DW_SPI_DR);
+		rxw = dw_read_io_reg(dws, DW_SPI_DR);
 		/* Care rx only if the transfer's original "rx" is 

not null */
 		if (dws->rx_end - dws->len) {
 			if (dws->n_bytes == 1)

diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
index 6c91391..b75ed32 100644
--- a/drivers/spi/spi-dw.h
+++ b/drivers/spi/spi-dw.h

@@ -109,6 +109,7 @@ struct dw_spi {
 	u32			fifo_len;	/* depth of the FIFO 

buffer */
 	u32			max_freq;	/* max bus freq 
supported */
 
+	u32			reg_io_width;	/* DR I/O width in 
bytes */
 	u16			bus_num;
 	u16			num_cs;		/* supported 
slave numbers */
 

@@ -145,11 +146,45 @@ static inline u32 dw_readl(struct dw_spi *dws, 

u32 offset)
 	return __raw_readl(dws->regs + offset);
 }
 
+static inline u16 dw_readw(struct dw_spi *dws, u32 offset)
+{
+	return __raw_readw(dws->regs + offset);
+}
+
 static inline void dw_writel(struct dw_spi *dws, u32 offset, u32 
val)
 {
 	__raw_writel(val, dws->regs + offset);
 }
 
+static inline void dw_writew(struct dw_spi *dws, u32 offset, u16 
val)
+{
+	__raw_writew(val, dws->regs + offset);
+}
+
+static inline u32 dw_read_io_reg(struct dw_spi *dws, u32 offset)
+{
+	switch (dws->reg_io_width) {
+	case 2:
+		return dw_readw(dws, offset);
+	case 4:
+	default:
+		return dw_readl(dws, offset);
+	}
+}
+
+static inline void dw_write_io_reg(struct dw_spi *dws, u32 offset, 
u32 val)
+{
+	switch (dws->reg_io_width) {
+	case 2:
+		dw_writew(dws, offset, val);
+		break;
+	case 4:
+	default:
+		dw_writel(dws, offset, val);
+		break;
+	}
+}
+
 static inline void spi_enable_chip(struct dw_spi *dws, int enable)
 {
 	dw_writel(dws, DW_SPI_SSIENR, (enable ? 1 : 0));