This add support for the RX_SAMPLE_DLY register. If enabled in the
Designware IP, it allows tuning of the rx data signal by means of an
internal rx sample fifo.

The register is located at offset 0xf0, and if the option is not
enabled in the IP, changing the register will have no effect.

Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Lars Povlsen <redacted>
---
 drivers/spi/spi-dw.c | 7 +++++++
 drivers/spi/spi-dw.h | 2 ++
 2 files changed, 9 insertions(+)

diff --git a/drivers/spi/spi-dw.c b/drivers/spi/spi-dw.c
index e572eb34a3c1a..32997f28fa5bb 100644
--- a/drivers/spi/spi-dw.c
+++ b/drivers/spi/spi-dw.c

@@ -81,6 +81,9 @@ static ssize_t dw_spi_show_regs(struct file *file, char __user *user_buf,
 			"DMATDLR: \t0x%08x\n", dw_readl(dws, DW_SPI_DMATDLR));
 	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"DMARDLR: \t0x%08x\n", dw_readl(dws, DW_SPI_DMARDLR));

 	len += scnprintf(buf + len, SPI_REGS_BUFSIZE - len,
 			"=================================\n");

@@ -315,6 +318,10 @@ static int dw_spi_transfer_one(struct spi_controller *master,
 		spi_set_clk(dws, chip->clk_div);
 	}

+	if (dws->rx_sample_dly)
+		dw_writel(dws, DW_SPI_RX_SAMPLE_DLY, dws->rx_sample_dly);
+
 	dws->n_bytes = DIV_ROUND_UP(transfer->bits_per_word, BITS_PER_BYTE);
 	dws->dma_width = DIV_ROUND_UP(transfer->bits_per_word, BITS_PER_BYTE);

diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
index 1bf5713e047d3..ed6e47b3f50da 100644
--- a/drivers/spi/spi-dw.h
+++ b/drivers/spi/spi-dw.h

@@ -31,6 +31,7 @@
 #define DW_SPI_IDR			0x58
 #define DW_SPI_VERSION			0x5c
 #define DW_SPI_DR			0x60
+#define DW_SPI_RX_SAMPLE_DLY		0xf0
 #define DW_SPI_CS_OVERRIDE		0xf4

 /* Bit fields in CTRLR0 */

@@ -111,6 +112,7 @@ struct dw_spi {

 	int			cs_override;
 	u32			reg_io_width;	/* DR I/O width in bytes */