spi: dw: Add Microchip Sparx5 support

This adds SPI support for the Sparx5 SoC, which is using the MMIO
Designware SPI controller.

The Sparx5 differs from the Ocelot version in these areas:

 * The CS override is controlled by a new set of registers for
   this purpose.

 * The Sparx5 SPI controller has the RX sample delay register, and it
   must be configured for the (SPI NAND) device on SPI2.

 * The Sparx5 SPI controller has 2 different SPI bus interfaces on the
   same controller (don't ask...). The "spi-mux" driver should be used
   in conjunction with the SPI driver to select the appropriate bus.
Signed-off-by: Lars Povlsen <lars.povlsen@microchip.com>
Link: https://lore.kernel.org/r/20200824203010.2033-3-lars.povlsen@microchip.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-dw-mmio.c

@@ -45,6 +45,9 @@ struct dw_spi_mmio {
 #define MSCC_SPI_MST_SW_MODE_SW_PIN_CTRL_MODE	BIT(13)
 #define MSCC_SPI_MST_SW_MODE_SW_SPI_CS(x)	(x << 5)
 
+#define SPARX5_FORCE_ENA			0xa4
+#define SPARX5_FORCE_VAL			0xa8
+
 /*
  * For Keem Bay, CTRLR0[31] is used to select controller mode.
  * 0: SSI is slave
@@ -54,7 +57,7 @@ struct dw_spi_mmio {
 
 struct dw_spi_mscc {
 	struct regmap       *syscon;
-	void __iomem        *spi_mst;
+	void __iomem        *spi_mst; /* Not sparx5 */
 };
 
 /*
@@ -134,6 +137,70 @@ static int dw_spi_mscc_jaguar2_init(struct platform_device *pdev,
 				JAGUAR2_IF_SI_OWNER_OFFSET);
 }
 
+/*
+ * The Designware SPI controller (referred to as master in the
+ * documentation) automatically deasserts chip select when the tx fifo
+ * is empty. The chip selects then needs to be driven by a CS override
+ * register. enable is an active low signal.
+ */
+static void dw_spi_sparx5_set_cs(struct spi_device *spi, bool enable)
+{
+	struct dw_spi *dws = spi_master_get_devdata(spi->master);
+	struct dw_spi_mmio *dwsmmio = container_of(dws, struct dw_spi_mmio, dws);
+	struct dw_spi_mscc *dwsmscc = dwsmmio->priv;
+	u8 cs = spi->chip_select;
+
+	if (!enable) {
+		/* CS override drive enable */
+		regmap_write(dwsmscc->syscon, SPARX5_FORCE_ENA, 1);
+		/* Now set CSx enabled */
+		regmap_write(dwsmscc->syscon, SPARX5_FORCE_VAL, ~BIT(cs));
+		/* Allow settle */
+		usleep_range(1, 5);
+	} else {
+		/* CS value */
+		regmap_write(dwsmscc->syscon, SPARX5_FORCE_VAL, ~0);
+		/* Allow settle */
+		usleep_range(1, 5);
+		/* CS override drive disable */
+		regmap_write(dwsmscc->syscon, SPARX5_FORCE_ENA, 0);
+	}
+
+	dw_spi_set_cs(spi, enable);
+}
+
+static int dw_spi_mscc_sparx5_init(struct platform_device *pdev,
+				   struct dw_spi_mmio *dwsmmio)
+{
+	const char *syscon_name = "microchip,sparx5-cpu-syscon";
+	struct device *dev = &pdev->dev;
+	struct dw_spi_mscc *dwsmscc;
+
+	if (!IS_ENABLED(CONFIG_SPI_MUX)) {
+		dev_err(dev, "This driver needs CONFIG_SPI_MUX\n");
+		return -EOPNOTSUPP;
+	}
+
+	dwsmscc = devm_kzalloc(dev, sizeof(*dwsmscc), GFP_KERNEL);
+	if (!dwsmscc)
+		return -ENOMEM;
+
+	dwsmscc->syscon =
+		syscon_regmap_lookup_by_compatible(syscon_name);
+	if (IS_ERR(dwsmscc->syscon)) {
+		dev_err(dev, "No syscon map %s\n", syscon_name);
+		return PTR_ERR(dwsmscc->syscon);
+	}
+
+	dwsmmio->dws.set_cs = dw_spi_sparx5_set_cs;
+	dwsmmio->priv = dwsmscc;
+
+	/* Register hook to configure CTRLR0 */
+	dwsmmio->dws.update_cr0 = dw_spi_update_cr0;
+
+	return 0;
+}
+
 static int dw_spi_alpine_init(struct platform_device *pdev,
 			      struct dw_spi_mmio *dwsmmio)
 {
@@ -297,6 +364,7 @@ static const struct of_device_id dw_spi_mmio_of_match[] = {
 	{ .compatible = "renesas,rzn1-spi", .data = dw_spi_dw_apb_init},
 	{ .compatible = "snps,dwc-ssi-1.01a", .data = dw_spi_dwc_ssi_init},
 	{ .compatible = "intel,keembay-ssi", .data = dw_spi_keembay_init},
+	{ .compatible = "microchip,sparx5-spi", dw_spi_mscc_sparx5_init},
 	{ /* end of table */}
 };
 MODULE_DEVICE_TABLE(of, dw_spi_mmio_of_match);