spi: dw: Add support for AMD Pensando Elba SoC

The AMD Pensando Elba SoC includes a DW apb_ssi v4 controller
with device specific chip-select control.  The Elba SoC
provides four chip-selects where the native DW IP supports
two chip-selects.  The Elba DW_SPI instance has two native
CS signals that are always overridden.

Signed-off-by: Brad Larson <blarson@amd.com>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/r/20230410184526.15990-11-blarson@amd.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-dw-mmio.c

@@ -53,6 +53,20 @@ struct dw_spi_mscc {
 	void __iomem        *spi_mst; /* Not sparx5 */
 };
 
+/*
+ * Elba SoC does not use ssi, pin override is used for cs 0,1 and
+ * gpios for cs 2,3 as defined in the device tree.
+ *
+ * cs:  |       1               0
+ * bit: |---3-------2-------1-------0
+ *      |  cs1   cs1_ovr   cs0   cs0_ovr
+ */
+#define ELBA_SPICS_REG			0x2468
+#define ELBA_SPICS_OFFSET(cs)		((cs) << 1)
+#define ELBA_SPICS_MASK(cs)		(GENMASK(1, 0) << ELBA_SPICS_OFFSET(cs))
+#define ELBA_SPICS_SET(cs, val)		\
+		((((val) << 1) | BIT(0)) << ELBA_SPICS_OFFSET(cs))
+
 /*
  * The Designware SPI controller (referred to as master in the documentation)
  * automatically deasserts chip select when the tx fifo is empty. The chip
@@ -237,6 +251,49 @@ static int dw_spi_canaan_k210_init(struct platform_device *pdev,
 	return 0;
 }
 
+static void dw_spi_elba_override_cs(struct regmap *syscon, int cs, int enable)
+{
+	regmap_update_bits(syscon, ELBA_SPICS_REG, ELBA_SPICS_MASK(cs),
+			   ELBA_SPICS_SET(cs, enable));
+}
+
+static void dw_spi_elba_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 regmap *syscon = dwsmmio->priv;
+	u8 cs;
+
+	cs = spi->chip_select;
+	if (cs < 2)
+		dw_spi_elba_override_cs(syscon, spi->chip_select, enable);
+
+	/*
+	 * The DW SPI controller needs a native CS bit selected to start
+	 * the serial engine.
+	 */
+	spi->chip_select = 0;
+	dw_spi_set_cs(spi, enable);
+	spi->chip_select = cs;
+}
+
+static int dw_spi_elba_init(struct platform_device *pdev,
+			    struct dw_spi_mmio *dwsmmio)
+{
+	struct regmap *syscon;
+
+	syscon = syscon_regmap_lookup_by_phandle(dev_of_node(&pdev->dev),
+						 "amd,pensando-elba-syscon");
+	if (IS_ERR(syscon))
+		return dev_err_probe(&pdev->dev, PTR_ERR(syscon),
+				     "syscon regmap lookup failed\n");
+
+	dwsmmio->priv = syscon;
+	dwsmmio->dws.set_cs = dw_spi_elba_set_cs;
+
+	return 0;
+}
+
 static int dw_spi_mmio_probe(struct platform_device *pdev)
 {
 	int (*init_func)(struct platform_device *pdev,
@@ -350,6 +407,7 @@ static const struct of_device_id dw_spi_mmio_of_match[] = {
 	{ .compatible = "intel,thunderbay-ssi", .data = dw_spi_intel_init},
 	{ .compatible = "microchip,sparx5-spi", dw_spi_mscc_sparx5_init},
 	{ .compatible = "canaan,k210-spi", dw_spi_canaan_k210_init},
+	{ .compatible = "amd,pensando-elba-spi", .data = dw_spi_elba_init},
 	{ /* end of table */}
 };
 MODULE_DEVICE_TABLE(of, dw_spi_mmio_of_match);