[PATCH RFC 5/9] drm/bridge: tc358762: add SPI master support to control panels

[Andreas Kemnade]

To allow to use panels with their SPI port connected to the bridge, add
SPI master support. Due to lack of a complete datasheet, mode and speed
are not configurable. It is also unclear how CS behaves.

Signed-off-by: Andreas Kemnade <andreas@xxxxxxxxxxxx>
---
 drivers/gpu/drm/bridge/tc358762.c | 72 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 71 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/tc358762.c b/drivers/gpu/drm/bridge/tc358762.c
index ec72e6e92b46..8024e49e2868 100644
--- a/drivers/gpu/drm/bridge/tc358762.c
+++ b/drivers/gpu/drm/bridge/tc358762.c
@@ -16,6 +16,9 @@
 #include <linux/module.h>
 #include <linux/of_graph.h>
 #include <linux/regulator/consumer.h>
+#include <linux/spi/spi.h>
+
+#include <linux/unaligned.h>
 
 #include <video/mipi_display.h>
 #include <video/videomode.h>
@@ -72,7 +75,11 @@
 
 /* SPI Master Registers */
 #define SPICMR			0x0450
-#define SPITCR			0x0454
+#define SPI_SEL_CS0		0x0002
+
+#define SPITCR1			0x0454
+
+#define WCMDQUE			0x0500
 
 /* System Controller Registers */
 #define SYSCTRL			0x0464
@@ -98,6 +105,7 @@ struct tc358762 {
 	struct regulator *regulator;
 	struct drm_bridge *panel_bridge;
 	struct gpio_desc *reset_gpio;
+	struct spi_controller *spi;
 	bool pre_enabled;
 	int error;
 	bool use_vtg;
@@ -252,11 +260,25 @@ static void tc358762_pre_enable(struct drm_bridge *bridge,
 
 	tc358762_write(ctx, LCDCTRL, lcdctrl);
 
+	/*
+	 * value just copied from vendor driver, no idea which settings
+	 * are configured
+	 */
+	if (ctx->spi)
+		tc358762_write(ctx, SPITCR1, 0x00000122);
+
 	tc358762_write(ctx, PPI_STARTPPI, PPI_STARTPPI_STARTPPI);
 	tc358762_write(ctx, DSI_STARTDSI, DSI_STARTDSI_STARTDSI);
 
 	msleep(100);
 
+	/*
+	 * no idea when CS is actually asserted, maybe once per handling of
+	 * one packet written to WCMDQUE? Maybe just after setting SPI_SEL_CS0
+	 */
+	if (ctx->spi)
+		tc358762_write(ctx, SPICMR, SPI_SEL_CS0);
+
 	ret = tc358762_clear_error(ctx);
 	if (ret < 0)
 		dev_err(ctx->dev, "error initializing bridge (%d)\n", ret);
@@ -308,6 +330,40 @@ static int tc358762_parse_dt(struct tc358762 *ctx)
 	return 0;
 }
 
+static int tc358762_spi_transfer_one(struct spi_controller *ctlr,
+				     struct spi_device *spi,
+				     struct spi_transfer *t)
+{
+	struct tc358762 *ctx = spi_controller_get_devdata(ctlr);
+	struct mipi_dsi_device *dsi = to_mipi_dsi_device(ctx->dev);
+	/*
+	 * limits to be determined, just define something which is
+	 * enough for current use case.
+	 */
+	u8 data[8];
+
+	if (!ctx->pre_enabled)
+		return -ENODEV;
+
+	if (t->len > sizeof(data) - 2)
+		return -EOVERFLOW;
+
+	/*
+	 * half duplex is supported by the bridge,
+	 * but due to lack of testing possibilities, support only simplex write
+	 */
+	if (t->rx_buf)
+		return -EINVAL;
+
+	if (!t->tx_buf)
+		return -EINVAL;
+
+	put_unaligned_le16(WCMDQUE, data);
+	memcpy(data + 2, t->tx_buf, t->len);
+
+	return mipi_dsi_generic_write(dsi, data, t->len + 2);
+}
+
 static int tc358762_configure_regulators(struct tc358762 *ctx)
 {
 	ctx->regulator = devm_regulator_get(ctx->dev, "vddc");
@@ -321,6 +377,7 @@ static int tc358762_probe(struct mipi_dsi_device *dsi)
 {
 	struct device *dev = &dsi->dev;
 	struct tc358762 *ctx;
+	struct device_node *spi_node;
 	int ret;
 
 	ctx = devm_drm_bridge_alloc(dev, struct tc358762, bridge,
@@ -333,6 +390,19 @@ static int tc358762_probe(struct mipi_dsi_device *dsi)
 	ctx->dev = dev;
 	ctx->pre_enabled = false;
 
+	if (IS_ENABLED(CONFIG_SPI)) {
+		spi_node = of_get_child_by_name(dev->of_node, "spi");
+		if (spi_node) {
+			ctx->spi = devm_spi_alloc_host(dev, 0);
+			spi_controller_set_devdata(ctx->spi, ctx);
+			ctx->spi->transfer_one = tc358762_spi_transfer_one;
+			ctx->spi->dev.of_node = spi_node;
+			ret = devm_spi_register_controller(dev, ctx->spi);
+			if (ret < 0)
+				return dev_err_probe(dev, ret, "register spi controller  failed\n");
+		}
+	}
+
 	/* Always use VTG */
 	ctx->use_vtg = true;
 

-- 
2.47.3