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From: Svyatoslav Ryhel <clamor95@gmail.com>
To: Neil Armstrong <neil.armstrong@linaro.org>,
	Jessica Zhang <jesszhan0024@gmail.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@gmail.com>,
	Simona Vetter <simona@ffwll.ch>,
	Rob Herring <robh@kernel.org>,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Thierry Reding <thierry.reding@kernel.org>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Mikko Perttunen <mperttunen@nvidia.com>,
	Svyatoslav Ryhel <clamor95@gmail.com>
Cc: dri-devel@lists.freedesktop.org,
	devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-tegra@vger.kernel.org
Subject: [PATCH v3 4/7] drm/tegra: Add support for 8-bit CPU interface
Date: Mon, 19 Oct 2026 12:57:02 +0300
Message-ID: <20261019095705.91062-5-clamor95@gmail.com>
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The display controller in Tegra20/30 SoCs features an 8-bit SPI interface
that closely resembles the MIPI DBI Type B protocol and is referred to as
'8-bit CPU'. Each display controller provides two such interfaces, which
can be used to send MIPI DCS commands to initialize and control the panel
while image data is transmitted via 16/18/24-line RGB.

The '8-bit CPU', although being the DC interface, is modeled using a
bridge framework for flexibility and convenience. This implementation does
not change the existing codebase besides registering a fragment and can be
enabled/disabled without losing other Tegra DRM functionality.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
---
 drivers/gpu/drm/tegra/Kconfig  |   7 +
 drivers/gpu/drm/tegra/Makefile |   3 +
 drivers/gpu/drm/tegra/dbi.c    | 415 +++++++++++++++++++++++++++++++++
 drivers/gpu/drm/tegra/dc.c     |  29 +++
 drivers/gpu/drm/tegra/dc.h     |   1 +
 drivers/gpu/drm/tegra/trace.c  |   3 +
 6 files changed, 458 insertions(+)
 create mode 100644 drivers/gpu/drm/tegra/dbi.c

diff --git a/drivers/gpu/drm/tegra/Kconfig b/drivers/gpu/drm/tegra/Kconfig
index 8a3b16aac5d68..ce3a424398713 100644
--- a/drivers/gpu/drm/tegra/Kconfig
+++ b/drivers/gpu/drm/tegra/Kconfig
@@ -30,6 +30,13 @@ config DRM_TEGRA
 
 if DRM_TEGRA
 
+config DRM_TEGRA_DBI
+	tristate "Enable MIPI DBI type B communication protocol for Tegra 20/30"
+	help
+	  Tegra20 and Tegra30 feature 8 bit CPU driver panel control
+	  protocol (similar to MIPI DBI Type B). This option allows use
+	  it to set up and control compatible panel.
+
 config DRM_TEGRA_DEBUG
 	bool "NVIDIA Tegra DRM debug support"
 	help
diff --git a/drivers/gpu/drm/tegra/Makefile b/drivers/gpu/drm/tegra/Makefile
index e399b40d64a1d..d67e53248a082 100644
--- a/drivers/gpu/drm/tegra/Makefile
+++ b/drivers/gpu/drm/tegra/Makefile
@@ -33,3 +33,6 @@ tegra-drm-y += trace.o
 tegra-drm-$(CONFIG_DRM_FBDEV_EMULATION) += fbdev.o
 
 obj-$(CONFIG_DRM_TEGRA) += tegra-drm.o
+
+obj-$(CONFIG_DRM_TEGRA_DBI) += tegra-dbi.o
+tegra-dbi-y := dbi.o
diff --git a/drivers/gpu/drm/tegra/dbi.c b/drivers/gpu/drm/tegra/dbi.c
new file mode 100644
index 0000000000000..4b3966dea0438
--- /dev/null
+++ b/drivers/gpu/drm/tegra/dbi.c
@@ -0,0 +1,415 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/gpio/consumer.h>
+#include <linux/kernel.h>
+#include <linux/media-bus-format.h>
+#include <linux/module.h>
+#include <linux/of_platform.h>
+#include <linux/property.h>
+#include <linux/platform_device.h>
+
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_bridge.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_mipi_dbi.h>
+#include <drm/drm_of.h>
+#include <drm/drm_panel.h>
+
+#include <video/mipi_display.h>
+
+#include "dc.h"
+
+#define TEGRA_DBI_COMMAND			0
+#define TEGRA_DBI_DATA				1
+#define TEGRA_DBI_DATA_PINS_MAX			8
+
+struct tegra_dbi_output {
+	struct drm_panel *panel;
+	struct drm_bridge *bridge;
+};
+
+struct tegra_dbi_priv {
+	struct mipi_dbi dbi;		/* must be first */
+	struct device *dev;
+	struct tegra_dc *dc;
+
+	struct gpio_desc *dc_gpio;
+	struct gpio_desc *rw_gpio;
+	struct gpio_desc *cs_gpio;
+	struct gpio_descs *data_gpios;
+
+	struct drm_bridge bridge;
+	struct tegra_dbi_output output;
+
+	u32 spi_init_seq[4];
+	u32 bus_width;
+	bool prepared;
+};
+
+static inline struct tegra_dbi_priv *mipi_dbi_to_tegra_dbi(struct mipi_dbi *dbi)
+{
+	return container_of(dbi, struct tegra_dbi_priv, dbi);
+}
+
+static inline struct tegra_dbi_priv *bridge_to_tegra_dbi(struct drm_bridge *bridge)
+{
+	return container_of(bridge, struct tegra_dbi_priv, bridge);
+}
+
+static void tegra_dbi_write(struct tegra_dbi_priv *priv, u8 type, u8 value)
+{
+	DECLARE_BITMAP(value_bitmap, 8);
+
+	value_bitmap[0] = value;
+
+	gpiod_set_value(priv->dc_gpio, type);
+
+	gpiod_set_value(priv->cs_gpio, 0);
+	gpiod_set_value(priv->rw_gpio, 0);
+
+	gpiod_set_array_value(priv->data_gpios->ndescs, priv->data_gpios->desc,
+			      priv->data_gpios->info, value_bitmap);
+
+	gpiod_set_value(priv->cs_gpio, 1);
+	gpiod_set_value(priv->rw_gpio, 1);
+
+	udelay(10);
+}
+
+static int tegra_dbi_dbi_command(struct mipi_dbi *dbi, u8 *cmd, u8 *param, size_t num)
+{
+	struct tegra_dbi_priv *priv = mipi_dbi_to_tegra_dbi(dbi);
+	u8 command = *cmd;
+
+	if (!priv->data_gpios)
+		return 0;
+
+	tegra_dbi_write(priv, TEGRA_DBI_COMMAND, command);
+
+	for (int i = 0; i < num; i++)
+		tegra_dbi_write(priv, TEGRA_DBI_DATA, param[i]);
+
+	return 0;
+}
+
+static int tegra_dbi_prepare_gpios(struct tegra_dbi_priv *priv)
+{
+	struct device *dev = priv->dev;
+	int ret;
+
+	if (priv->prepared)
+		return 0;
+
+	/*
+	 * Control and data GPIOs are shared between SPI and DPI. The bridge
+	 * driver must get and put the required GPIOs each time DCS commands
+	 * are transmitted.
+	 */
+
+	priv->cs_gpio = gpiod_get(dev, "cs", GPIOD_OUT_HIGH);
+	if (IS_ERR(priv->cs_gpio)) {
+		dev_err(dev, "Failed to get CS GPIO: %ld\n", PTR_ERR(priv->cs_gpio));
+		return PTR_ERR(priv->cs_gpio);
+	}
+
+	priv->rw_gpio = gpiod_get(dev, "rw", GPIOD_OUT_HIGH);
+	if (IS_ERR(priv->rw_gpio)) {
+		ret = PTR_ERR(priv->rw_gpio);
+		dev_err(dev, "Failed to get RW GPIO: %d\n", ret);
+		goto free_cs;
+	}
+
+	priv->dc_gpio = gpiod_get(dev, "dc", GPIOD_OUT_LOW);
+	if (IS_ERR(priv->dc_gpio)) {
+		ret = PTR_ERR(priv->dc_gpio);
+		dev_err(dev, "Failed to get DC GPIO: %d\n", ret);
+		goto free_rw;
+	}
+
+	priv->data_gpios = gpiod_get_array(dev, "data", GPIOD_OUT_LOW);
+	if (IS_ERR(priv->data_gpios)) {
+		ret = PTR_ERR(priv->data_gpios);
+		dev_err(dev, "Failed to get data gpios %d\n", ret);
+		goto free_dc;
+	}
+
+	if (priv->data_gpios && priv->data_gpios->ndescs > TEGRA_DBI_DATA_PINS_MAX) {
+		ret = -EINVAL;
+		dev_err(dev, "Too many data gpios\n");
+		goto free_data;
+	}
+
+	priv->prepared = true;
+
+	return 0;
+
+free_data:
+	gpiod_put_array(priv->data_gpios);
+free_dc:
+	gpiod_put(priv->dc_gpio);
+free_rw:
+	gpiod_put(priv->rw_gpio);
+free_cs:
+	gpiod_put(priv->cs_gpio);
+
+	return ret;
+}
+
+static void tegra_dbi_atomic_enable(struct drm_bridge *bridge,
+				    struct drm_atomic_commit *state)
+{
+	struct tegra_dbi_priv *priv = bridge_to_tegra_dbi(bridge);
+	struct tegra_dc *dc = priv->dc;
+	u32 value;
+	int ret;
+
+	value = tegra_dc_readl(dc, DC_CMD_DISPLAY_COMMAND);
+	value &= ~DISP_CTRL_MODE_MASK;
+	tegra_dc_writel(dc, value, DC_CMD_DISPLAY_COMMAND);
+
+	/* Disable all options except cursor if enabled */
+	value = tegra_dc_readl(dc, DC_DISP_DISP_WIN_OPTIONS);
+	value &= CURSOR_ENABLE;
+	tegra_dc_writel(dc, value, DC_DISP_DISP_WIN_OPTIONS);
+
+	tegra_dc_commit(dc);
+
+	tegra_dc_writel(dc, V_PULSE1_ENABLE, DC_DISP_DISP_SIGNAL_OPTIONS0);
+	tegra_dc_writel(dc, PULSE_POLARITY_LOW, DC_DISP_V_PULSE1_CONTROL);
+
+	tegra_dc_writel(dc, PULSE_END(1), DC_DISP_V_PULSE0_POSITION_A);
+	tegra_dc_writel(dc, 0, DC_DISP_V_PULSE0_POSITION_B);
+	tegra_dc_writel(dc, 0, DC_DISP_V_PULSE0_POSITION_C);
+
+	value = 1 << FRAME_INIT_SEQ_CYCLES_SHIFT |
+		DC_SIGNAL_VPULSE1 << INIT_SEQ_DC_SIGNAL_SHIFT |
+		INIT_SEQUENCE_MODE_PLCD | SEND_INIT_SEQUENCE;
+	tegra_dc_writel(dc, value, DC_DISP_INIT_SEQ_CONTROL);
+
+	tegra_dc_writel(dc, priv->spi_init_seq[0], DC_DISP_SPI_INIT_SEQ_DATA_A);
+	tegra_dc_writel(dc, priv->spi_init_seq[1], DC_DISP_SPI_INIT_SEQ_DATA_B);
+	tegra_dc_writel(dc, priv->spi_init_seq[2], DC_DISP_SPI_INIT_SEQ_DATA_C);
+	tegra_dc_writel(dc, priv->spi_init_seq[3], DC_DISP_SPI_INIT_SEQ_DATA_D);
+
+	value = tegra_dc_readl(dc, DC_CMD_DISPLAY_COMMAND);
+	value &= ~DISP_CTRL_MODE_MASK;
+	value |= DISP_CTRL_MODE_C_DISPLAY;
+	tegra_dc_writel(dc, value, DC_CMD_DISPLAY_COMMAND);
+
+	/* set LDC pin to V Pulse 1 */
+	value = tegra_dc_readl(dc, DC_COM_PIN_OUTPUT_SELECT(6));
+	value |= LDC_OUTPUT_SELECT_V_PULSE1;
+	tegra_dc_writel(dc, value, DC_COM_PIN_OUTPUT_SELECT(6));
+
+	value = SC1_H_QUALIFIER(SC_H_QUALIFIER_NONE) |
+		SC0_V_QUALIFIER(SC_V_QUALIFIER_VACTIVE) |
+		SC0_H_QUALIFIER(SC_H_QUALIFIER_HACTIVE);
+	tegra_dc_writel(dc, value, DC_DISP_SHIFT_CLOCK_OPTIONS);
+
+	value = tegra_dc_readl(dc, DC_DISP_DISP_COLOR_CONTROL);
+	value &= ~BASE_COLOR_SIZE_MASK;
+
+	switch (priv->bus_width) {
+	case 16:
+		value |= BASE_COLOR_SIZE_565;
+		break;
+	case 18:
+		value |= BASE_COLOR_SIZE_666;
+		break;
+	case 24:
+	default:
+		value |= BASE_COLOR_SIZE_888;
+		break;
+	}
+
+	tegra_dc_writel(dc, value, DC_DISP_DISP_COLOR_CONTROL);
+
+	ret = tegra_dbi_prepare_gpios(priv);
+	if (ret)
+		return;
+
+	if (priv->output.panel)
+		drm_panel_enable(priv->output.panel);
+
+	gpiod_set_value(priv->cs_gpio, 0);
+
+	gpiod_put(priv->dc_gpio);
+	gpiod_put(priv->rw_gpio);
+	gpiod_put(priv->cs_gpio);
+
+	gpiod_put_array(priv->data_gpios);
+	priv->prepared = false;
+}
+
+static void tegra_dbi_atomic_disable(struct drm_bridge *bridge,
+				     struct drm_atomic_commit *state)
+{
+	struct tegra_dbi_priv *priv = bridge_to_tegra_dbi(bridge);
+	int ret;
+
+	ret = tegra_dbi_prepare_gpios(priv);
+	if (ret)
+		return;
+
+	if (priv->output.panel)
+		drm_panel_disable(priv->output.panel);
+
+	gpiod_set_value(priv->cs_gpio, 0);
+
+	gpiod_put(priv->dc_gpio);
+	gpiod_put(priv->rw_gpio);
+	gpiod_put(priv->cs_gpio);
+
+	gpiod_put_array(priv->data_gpios);
+	priv->prepared = false;
+}
+
+static int tegra_dbi_atomic_check(struct drm_bridge *bridge,
+				  struct drm_bridge_state *bridge_state,
+				  struct drm_crtc_state *crtc_state,
+				  struct drm_connector_state *conn_state)
+{
+	struct drm_display_mode *adjusted_mode = &crtc_state->adjusted_mode;
+
+	/* Set safe default bus flags if panel does not specify them */
+	if (!bridge_state->input_bus_cfg.flags)
+		bridge_state->input_bus_cfg.flags = bridge->timings->input_bus_flags;
+
+	/* Default to positive sync */
+	if (!(adjusted_mode->flags &
+	      (DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_NHSYNC)))
+		adjusted_mode->flags |= DRM_MODE_FLAG_PHSYNC;
+
+	if (!(adjusted_mode->flags &
+	      (DRM_MODE_FLAG_PVSYNC | DRM_MODE_FLAG_NVSYNC)))
+		adjusted_mode->flags |= DRM_MODE_FLAG_PVSYNC;
+
+	return 0;
+}
+
+static int tegra_dbi_attach(struct drm_bridge *bridge,
+			    struct drm_encoder *encoder,
+			    enum drm_bridge_attach_flags flags)
+{
+	struct tegra_dbi_priv *priv = bridge_to_tegra_dbi(bridge);
+	struct device *dev = priv->dev;
+
+	priv->dc = dev_get_drvdata(dev->parent);
+	if (!priv->dc)
+		return -ENODEV;
+
+	return drm_bridge_attach(bridge->encoder, priv->output.bridge, bridge,
+				 flags);
+}
+
+static enum drm_mode_status tegra_dbi_mode_valid(struct drm_bridge *bridge,
+						 const struct drm_display_info *info,
+						 const struct drm_display_mode *mode)
+{
+	if (mode->hdisplay > 800)
+		return MODE_H_ILLEGAL;
+
+	if (mode->vdisplay > 800)
+		return MODE_V_ILLEGAL;
+
+	return MODE_OK;
+}
+
+static const struct drm_bridge_funcs tegra_dbi_funcs = {
+	.attach = tegra_dbi_attach,
+	.mode_valid = tegra_dbi_mode_valid,
+
+	.atomic_enable = tegra_dbi_atomic_enable,
+	.atomic_disable = tegra_dbi_atomic_disable,
+	.atomic_check = tegra_dbi_atomic_check,
+
+	.atomic_create_state = drm_atomic_helper_bridge_create_state,
+	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
+};
+
+static const struct drm_bridge_timings default_tegra_dbi_timings = {
+	.input_bus_flags = DRM_BUS_FLAG_PIXDATA_SAMPLE_POSEDGE |
+			   DRM_BUS_FLAG_SYNC_SAMPLE_NEGEDGE |
+			   DRM_BUS_FLAG_DE_HIGH,
+};
+
+static int tegra_dbi_probe(struct platform_device *pdev)
+{
+	struct tegra_dbi_priv *priv;
+	struct device *dev = &pdev->dev;
+	struct device_node *np = dev->of_node;
+	struct drm_bridge *bridge;
+	struct drm_panel *panel;
+	struct device_node *ep;
+	int ret;
+
+	priv = devm_drm_bridge_alloc(dev, struct tegra_dbi_priv, bridge,
+				     &tegra_dbi_funcs);
+	if (IS_ERR(priv))
+		return PTR_ERR(priv);
+
+	priv->dev = dev;
+
+	ret = device_property_read_u32_array(dev, "nvidia,init-sequence",
+					     priv->spi_init_seq, 4);
+	if (ret < 0)
+		return dev_err_probe(dev, ret, "Failed to get init sequence\n");
+
+	ret = devm_of_platform_populate(dev);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to probe children\n");
+
+	/* Initialize MIPI DBI interface */
+	mutex_init(&priv->dbi.cmdlock);
+	priv->dbi.command = tegra_dbi_dbi_command;
+
+	ret = drm_of_find_panel_or_bridge(np, 1, 0, &panel, &bridge);
+	if (ret)
+		return ret;
+
+	if (panel) {
+		bridge = devm_drm_panel_bridge_add_typed(dev, panel,
+							 DRM_MODE_CONNECTOR_DPI);
+		if (IS_ERR(bridge))
+			return PTR_ERR(bridge);
+	}
+
+	priv->output.bridge = bridge;
+	priv->output.panel = panel;
+
+	/* get input ep (port0/endpoint0) */
+	ret = -EINVAL;
+	ep = of_graph_get_endpoint_by_regs(np, 0, 0);
+	if (ep) {
+		ret = of_property_read_u32(ep, "bus-width", &priv->bus_width);
+		of_node_put(ep);
+	}
+
+	if (ret)
+		priv->bus_width = 24;
+
+	priv->bridge.of_node = np;
+	priv->bridge.timings = &default_tegra_dbi_timings;
+
+	ret = devm_drm_bridge_add(dev, &priv->bridge);
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to add bridge\n");
+
+	platform_set_drvdata(pdev, priv);
+
+	return 0;
+}
+
+static struct platform_driver tegra_dbi_driver = {
+	.driver.name = "tegra-dbi",
+	.probe = tegra_dbi_probe,
+};
+module_platform_driver(tegra_dbi_driver);
+
+MODULE_AUTHOR("Svyatoslav Ryhel <clamor95@gmail.com>");
+MODULE_DESCRIPTION("Nvidia Tegra20/30 MIPI-DBI Type B driver");
+MODULE_LICENSE("GPL");
diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c
index 5c67928bcabfa..8f12d30cd2d8b 100644
--- a/drivers/gpu/drm/tegra/dc.c
+++ b/drivers/gpu/drm/tegra/dc.c
@@ -223,6 +223,7 @@ void tegra_dc_commit(struct tegra_dc *dc)
 	tegra_dc_writel(dc, GENERAL_ACT_REQ << 8, DC_CMD_STATE_CONTROL);
 	tegra_dc_writel(dc, GENERAL_ACT_REQ, DC_CMD_STATE_CONTROL);
 }
+EXPORT_SYMBOL_GPL(tegra_dc_commit);
 
 static inline u32 compute_dda_inc(unsigned int in, unsigned int out, bool v,
 				  unsigned int bpp)
@@ -3279,9 +3280,15 @@ static int tegra_dc_init_opp_table(struct tegra_dc *dc)
 	return 0;
 }
 
+static void tegra_dc_release_dbi_pdev(void *pdev)
+{
+	platform_device_unregister(pdev);
+}
+
 static int tegra_dc_probe(struct platform_device *pdev)
 {
 	u64 dma_mask = dma_get_mask(pdev->dev.parent);
+	struct device_node *dbi_np;
 	struct tegra_dc *dc;
 	int err;
 
@@ -3382,6 +3389,28 @@ static int tegra_dc_probe(struct platform_device *pdev)
 		}
 	}
 
+	dbi_np = of_get_available_child_by_name(pdev->dev.of_node, "dbi");
+	if (dbi_np) {
+		struct platform_device_info dbi_info = {
+			.parent = &pdev->dev,
+			.name = "tegra-dbi",
+			.id = PLATFORM_DEVID_AUTO,
+			.fwnode = of_fwnode_handle(dbi_np),
+			.of_node_reused = true,
+		};
+
+		dc->dbi = platform_device_register_full(&dbi_info);
+		of_node_put(dbi_np);
+		if (IS_ERR(dc->dbi))
+			return dev_err_probe(&pdev->dev, PTR_ERR(dc->dbi),
+					     "Failed to create DBI device\n");
+
+		err = devm_add_action_or_reset(&pdev->dev, tegra_dc_release_dbi_pdev,
+					       dc->dbi);
+		if (err)
+			return err;
+	}
+
 	err = tegra_dc_rgb_probe(dc);
 	if (err < 0 && err != -ENODEV)
 		return dev_err_probe(&pdev->dev, err,
diff --git a/drivers/gpu/drm/tegra/dc.h b/drivers/gpu/drm/tegra/dc.h
index 7005df32f485f..27dbee57f8f72 100644
--- a/drivers/gpu/drm/tegra/dc.h
+++ b/drivers/gpu/drm/tegra/dc.h
@@ -95,6 +95,7 @@ struct tegra_dc {
 
 	struct tegra_output *rgb;
 	struct tegra_pmc *pmc;
+	struct platform_device *dbi;
 
 	struct tegra_dc_stats stats;
 	struct list_head list;
diff --git a/drivers/gpu/drm/tegra/trace.c b/drivers/gpu/drm/tegra/trace.c
index 006f65c72a344..3aeb3825e2100 100644
--- a/drivers/gpu/drm/tegra/trace.c
+++ b/drivers/gpu/drm/tegra/trace.c
@@ -1,2 +1,5 @@
 #define CREATE_TRACE_POINTS
 #include "trace.h"
+
+EXPORT_TRACEPOINT_SYMBOL_GPL(dc_readl);
+EXPORT_TRACEPOINT_SYMBOL_GPL(dc_writel);
-- 
2.53.0