dw: spi: add support for Amazon's Alpine spi controller

Add support for a new devicetree compatible string called
'amazon,alpine-apb-ssi', which is necessary for the Amazon Alpine spi
controller. 'amazon,alpine-dw-apb-ssi' is used in the dw spi driver if
specified in the devicetree. Otherwise, fall back to driver default
behavior, i.e. original dw IP hw driver behavior.

Signed-off-by: Talel Shenhar <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-dw-mmio.c

···
 				JAGUAR2_IF_SI_OWNER_OFFSET);
 }
 
+static int dw_spi_alpine_init(struct platform_device *pdev,
+			      struct dw_spi_mmio *dwsmmio)
+{
+	dwsmmio->dws.cs_override = 1;
+
+	return 0;
+}
+
 static int dw_spi_mmio_probe(struct platform_device *pdev)
 {
 	int (*init_func)(struct platform_device *pdev,
···
 	{ .compatible = "snps,dw-apb-ssi", },
 	{ .compatible = "mscc,ocelot-spi", .data = dw_spi_mscc_ocelot_init},
 	{ .compatible = "mscc,jaguar2-spi", .data = dw_spi_mscc_jaguar2_init},
+	{ .compatible = "amazon,alpine-dw-apb-ssi", .data = dw_spi_alpine_init},
 	{ /* end of table */}
 };
 MODULE_DEVICE_TABLE(of, dw_spi_mmio_of_match);

drivers/spi/spi-dw.c

···
 
 	if (!enable)
 		dw_writel(dws, DW_SPI_SER, BIT(spi->chip_select));
+	else if (dws->cs_override)
+		dw_writel(dws, DW_SPI_SER, 0);
 }
 EXPORT_SYMBOL_GPL(dw_spi_set_cs);
 
···
 		dws->fifo_len = (fifo == 1) ? 0 : fifo;
 		dev_dbg(dev, "Detected FIFO size: %u bytes\n", dws->fifo_len);
 	}
+
+	/* enable HW fixup for explicit CS deselect for Amazon's alpine chip */
+	if (dws->cs_override)
+		dw_writel(dws, DW_SPI_CS_OVERRIDE, 0xF);
 }
 
 int dw_spi_add_host(struct device *dev, struct dw_spi *dws)

drivers/spi/spi-dw.h

···
 #define DW_SPI_IDR			0x58
 #define DW_SPI_VERSION			0x5c
 #define DW_SPI_DR			0x60
+#define DW_SPI_CS_OVERRIDE		0xf4
 
 /* Bit fields in CTRLR0 */
 #define SPI_DFS_OFFSET			0
···
 	u32			fifo_len;	/* depth of the FIFO buffer */
 	u32			max_freq;	/* max bus freq supported */
 
+	int			cs_override;
 	u32			reg_io_width;	/* DR I/O width in bytes */
 	u16			bus_num;
 	u16			num_cs;		/* supported slave numbers */