[RFC PATCH 2/4] gpu/drm: Add SPI DBI host driver

[Paul Cercueil]

This driver will register a DBI host driver for panels connected over
SPI.

For now, only DBI type c3 is supported, which is a SPI protocol with 8
bits per word, with the data/command information carried by a separate
GPIO.

Signed-off-by: Paul Cercueil <paul at crapouillou.net>
---
 drivers/gpu/drm/bridge/Kconfig   |   8 ++
 drivers/gpu/drm/bridge/Makefile  |   1 +
 drivers/gpu/drm/bridge/dbi-spi.c | 159 +++++++++++++++++++++++++++++++
 3 files changed, 168 insertions(+)
 create mode 100644 drivers/gpu/drm/bridge/dbi-spi.c

diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
index aaed2347ace9..61587bc4d6e6 100644
--- a/drivers/gpu/drm/bridge/Kconfig
+++ b/drivers/gpu/drm/bridge/Kconfig
@@ -180,6 +180,14 @@ config DRM_TI_TPD12S015
 	  Texas Instruments TPD12S015 HDMI level shifter and ESD protection
 	  driver.
 
+config DRM_MIPI_DBI_SPI
+	tristate "SPI host support for MIPI DBI"
+	depends on OF && SPI
+	select DRM_MIPI_DSI
+	select DRM_MIPI_DBI
+	help
+	  Driver to support DBI over SPI.
+
 source "drivers/gpu/drm/bridge/analogix/Kconfig"
 
 source "drivers/gpu/drm/bridge/adv7511/Kconfig"
diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
index 6fb062b5b0f0..17fdf7de498d 100644
--- a/drivers/gpu/drm/bridge/Makefile
+++ b/drivers/gpu/drm/bridge/Makefile
@@ -18,6 +18,7 @@ obj-$(CONFIG_DRM_I2C_ADV7511) += adv7511/
 obj-$(CONFIG_DRM_TI_SN65DSI86) += ti-sn65dsi86.o
 obj-$(CONFIG_DRM_TI_TFP410) += ti-tfp410.o
 obj-$(CONFIG_DRM_TI_TPD12S015) += ti-tpd12s015.o
+obj-$(CONFIG_DRM_MIPI_DBI_SPI) += dbi-spi.o
 
 obj-y += analogix/
 obj-y += synopsys/
diff --git a/drivers/gpu/drm/bridge/dbi-spi.c b/drivers/gpu/drm/bridge/dbi-spi.c
new file mode 100644
index 000000000000..c790514b7372
--- /dev/null
+++ b/drivers/gpu/drm/bridge/dbi-spi.c
@@ -0,0 +1,159 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * MIPI Display Bus Interface (DBI) SPI support
+ *
+ * Copyright 2016 Noralf Trønnes
+ * Copyright 2020 Paul Cercueil <paul at crapouillou.net>
+ */
+
+#include <linux/gpio/consumer.h>
+#include <linux/module.h>
+#include <linux/spi/spi.h>
+
+#include <drm/drm_mipi_dbi.h>
+#include <drm/drm_mipi_dsi.h>
+
+#include <video/mipi_display.h>
+
+struct dbi_spi {
+	struct mipi_dsi_host host;
+	struct mipi_dsi_host_ops host_ops;
+
+	struct spi_device *spi;
+	struct gpio_desc *dc;
+	struct mutex cmdlock;
+};
+
+static inline struct dbi_spi *host_to_dbi_spi(struct mipi_dsi_host *host)
+{
+	return container_of(host, struct dbi_spi, host);
+}
+
+static ssize_t dbi_spi_transfer(struct mipi_dsi_host *host,
+				const struct mipi_dsi_msg *msg)
+{
+	struct dbi_spi *dbi = host_to_dbi_spi(host);
+	struct spi_device *spi = dbi->spi;
+	const u8 *buf = msg->tx_buf;
+	unsigned int bpw = 8;
+	u32 speed_hz;
+	ssize_t ret;
+
+	/* for now we only support sending messages, not receiving */
+	if (msg->rx_len)
+		return -ENOTSUPP;
+
+	gpiod_set_value_cansleep(dbi->dc, 0);
+
+	speed_hz = mipi_dbi_spi_cmd_max_speed(spi, 1);
+	ret = mipi_dbi_spi_transfer(spi, speed_hz, 8, buf, 1);
+	if (ret || msg->tx_len == 1)
+		return ret;
+
+	if (buf[0] == MIPI_DCS_WRITE_MEMORY_START)
+		bpw = 16;
+
+	gpiod_set_value_cansleep(dbi->dc, 1);
+	speed_hz = mipi_dbi_spi_cmd_max_speed(spi, msg->tx_len - 1);
+
+	ret = mipi_dbi_spi_transfer(spi, speed_hz, bpw,
+				    &buf[1], msg->tx_len - 1);
+	if (ret)
+		return ret;
+
+	return msg->tx_len;
+}
+
+static int dbi_spi_attach(struct mipi_dsi_host *host,
+			  struct mipi_dsi_device *dsi)
+{
+	return 0; /* Nothing to do */
+}
+
+static int dbi_spi_detach(struct mipi_dsi_host *host,
+			  struct mipi_dsi_device *dsi)
+{
+	return 0; /* Nothing to do */
+}
+
+static void dbi_spi_host_unregister(void *d)
+{
+	mipi_dsi_host_unregister(d);
+}
+
+static int dbi_spi_probe(struct spi_device *spi)
+{
+	struct device *dev = &spi->dev;
+	struct mipi_dsi_device_info info = { };
+	struct mipi_dsi_device *dsi;
+	struct dbi_spi *dbi;
+	int ret;
+
+	dbi = devm_kzalloc(dev, sizeof(*dbi), GFP_KERNEL);
+	if (!dbi)
+		return -ENOMEM;
+
+	/* Only DBI Type C3 supported for now */
+	dbi->host.bus_types = MIPI_DEVICE_TYPE_DBI_SPI_MODE3;
+
+	dbi->host.dev = dev;
+	dbi->host.ops = &dbi->host_ops;
+	dbi->spi = spi;
+	spi_set_drvdata(spi, dbi);
+
+	dbi->dc = devm_gpiod_get(dev, "dc", GPIOD_OUT_LOW);
+	if (IS_ERR(dbi->dc)) {
+		dev_err(dev, "Failed to get gpio 'dc'\n");
+		return PTR_ERR(dbi->dc);
+	}
+
+	dbi->host_ops.transfer = dbi_spi_transfer;
+	dbi->host_ops.attach = dbi_spi_attach;
+	dbi->host_ops.detach = dbi_spi_detach;
+
+	mutex_init(&dbi->cmdlock);
+
+	ret = mipi_dsi_host_register(&dbi->host);
+	if (ret) {
+		dev_err(dev, "Unable to register DSI host\n");
+		return ret;
+	}
+
+	ret = devm_add_action_or_reset(dev, dbi_spi_host_unregister, &dbi->host);
+	if (ret)
+		return ret;
+
+	/*
+	 * Register our own node as a MIPI DSI device.
+	 * This ensures that the panel driver will be probed.
+	 */
+	info.channel = 0;
+	info.node = of_node_get(dev->of_node);
+
+	dsi = mipi_dsi_device_register_full(&dbi->host, &info);
+	if (IS_ERR(dsi)) {
+		dev_err(dev, "Failed to add DSI device\n");
+		return PTR_ERR(dsi);
+	}
+
+	return 0;
+}
+
+static const struct of_device_id dbi_spi_of_match[] = {
+	{ .compatible = "adafruit,yx240qv29" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, dbi_spi_of_match);
+
+static struct spi_driver dbi_spi_driver = {
+	.driver = {
+		.name = "dbi-spi",
+		.of_match_table = dbi_spi_of_match,
+	},
+	.probe = dbi_spi_probe,
+};
+module_spi_driver(dbi_spi_driver);
+
+MODULE_DESCRIPTION("DBI SPI bus driver");
+MODULE_AUTHOR("Paul Cercueil <paul at crapouillou.net>");
+MODULE_LICENSE("GPL");
-- 
2.26.2