spi: axi-spi-engine: Add SPI_CS_HIGH support

The AXI SPI Engine IP core v1.2 added support for SPI_CS_HIGH. This
provides the driver implementation to make use of this feature when
supported hardware is detected.

Signed-off-by: David Lechner <[e-mail]>
Link: https://msgid.link/r/20240[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-axi-spi-engine.c

···
 #define SPI_ENGINE_INST_ASSERT			0x1
 #define SPI_ENGINE_INST_WRITE			0x2
 #define SPI_ENGINE_INST_MISC			0x3
+#define SPI_ENGINE_INST_CS_INV			0x4
 
 #define SPI_ENGINE_CMD_REG_CLK_DIV		0x0
 #define SPI_ENGINE_CMD_REG_CONFIG		0x1
···
 	SPI_ENGINE_CMD(SPI_ENGINE_INST_MISC, SPI_ENGINE_MISC_SLEEP, (delay))
 #define SPI_ENGINE_CMD_SYNC(id) \
 	SPI_ENGINE_CMD(SPI_ENGINE_INST_MISC, SPI_ENGINE_MISC_SYNC, (id))
+#define SPI_ENGINE_CMD_CS_INV(flags) \
+	SPI_ENGINE_CMD(SPI_ENGINE_INST_CS_INV, 0, (flags))
 
 struct spi_engine_program {
 	unsigned int length;
···
 	struct spi_engine_message_state msg_state;
 	struct completion msg_complete;
 	unsigned int int_enable;
+	/* shadows hardware CS inversion flag state */
+	u8 cs_inv;
 };
 
 static void spi_engine_program_add_cmd(struct spi_engine_program *p,
···
 	return 0;
 }
 
+static int spi_engine_setup(struct spi_device *device)
+{
+	struct spi_controller *host = device->controller;
+	struct spi_engine *spi_engine = spi_controller_get_devdata(host);
+
+	if (device->mode & SPI_CS_HIGH)
+		spi_engine->cs_inv |= BIT(spi_get_chipselect(device, 0));
+	else
+		spi_engine->cs_inv &= ~BIT(spi_get_chipselect(device, 0));
+
+	writel_relaxed(SPI_ENGINE_CMD_CS_INV(spi_engine->cs_inv),
+		       spi_engine->base + SPI_ENGINE_REG_CMD_FIFO);
+
+	/*
+	 * In addition to setting the flags, we have to do a CS assert command
+	 * to make the new setting actually take effect.
+	 */
+	writel_relaxed(SPI_ENGINE_CMD_ASSERT(0, 0xff),
+		       spi_engine->base + SPI_ENGINE_REG_CMD_FIFO);
+
+	return 0;
+}
+
 static int spi_engine_transfer_one_message(struct spi_controller *host,
 	struct spi_message *msg)
 {
···
 	host->optimize_message = spi_engine_optimize_message;
 	host->unoptimize_message = spi_engine_unoptimize_message;
 	host->num_chipselect = 8;
+
+	/* Some features depend of the IP core version. */
+	if (ADI_AXI_PCORE_VER_MINOR(version) >= 2) {
+		host->mode_bits |= SPI_CS_HIGH;
+		host->setup = spi_engine_setup;
+	}
 
 	if (host->max_speed_hz == 0)
 		return dev_err_probe(&pdev->dev, -EINVAL, "spi_clk rate is 0");