[PATCH 0/5] drm/rcar-du: Add support for DSI pipelines with DSC

[PATCH 0/5] drm/rcar-du: Add support for DSI pipelines with DSC

[Tomi Valkeinen]

Some DSI pipelines have DSC (Display Stream Compression) IP block
between the DU and the DSI. Even if DSC is not needed, the IP must be
enabled for the DSI output to work.

This series adds a basic DSC driver, so that the DSC IP gets enabled in
bypass mode. This enables DisplayPort output on Sparrow Hawk board, as
the DP output comes from DSI and sn65dsi86 bridge.

Original series from Marek.

Note: I see that not every run of kms++'s kmstest gives me a picture on
my monitor. Sometimes the monitor seems to be trying to repeatedly sync,
but fails, and the screen stays black. However, I see this same issue on
WhiteHawk, which uses DSI0 pipeline, without DSC, so I think that is a
separate issue.

 Tomi

Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
---
Marek Vasut (4):
      clk: renesas: r8a779g0: Add DSC clock
      dt-bindings: display: bridge: Document Renesas R-Car V4H DSC bindings
      drm/rcar-du: dsc: Add rudimentary Renesas R-Car V4H DSC driver
      arm64: dts: renesas: Add Renesas R-Car V4H DSC

Tomi Valkeinen (1):
      drm/rcar-du: dsi: Support DSC in the pipeline

 .../bindings/display/bridge/renesas,dsc.yaml       |  96 ++++++++++++
 arch/arm64/boot/dts/renesas/r8a779g0.dtsi          |  31 +++-
 .../boot/dts/renesas/r8a779g3-sparrow-hawk.dts     |   5 +
 drivers/clk/renesas/r8a779g0-cpg-mssr.c            |   1 +
 drivers/gpu/drm/renesas/rcar-du/Kconfig            |  13 ++
 drivers/gpu/drm/renesas/rcar-du/Makefile           |   1 +
 drivers/gpu/drm/renesas/rcar-du/rcar_dsc.c         | 163 +++++++++++++++++++++
 drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c    |  36 ++++-
 8 files changed, 343 insertions(+), 3 deletions(-)
---
base-commit: 028ef9c96e96197026887c0f092424679298aae8
change-id: 20260514-rcar-du-dsc-45bcf0c2fe86

Best regards,
-- 
Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>

[PATCH 1/5] clk: renesas: r8a779g0: Add DSC clock

[Tomi Valkeinen]

From: Marek Vasut <marek.vasut+renesas@mailbox.org>

Add the DSC module clock for Renesas R-Car V4H (R8A779G0) SoC.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
---
 drivers/clk/renesas/r8a779g0-cpg-mssr.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/clk/renesas/r8a779g0-cpg-mssr.c b/drivers/clk/renesas/r8a779g0-cpg-mssr.c
index 015b9773cc55..54ba76ff5ab0 100644
--- a/drivers/clk/renesas/r8a779g0-cpg-mssr.c
+++ b/drivers/clk/renesas/r8a779g0-cpg-mssr.c
@@ -245,6 +245,7 @@ static const struct mssr_mod_clk r8a779g0_mod_clks[] __initconst = {
 	DEF_MOD("fcpvx0",	1100,	R8A779G0_CLK_S0D1_VIO),
 	DEF_MOD("fcpvx1",	1101,	R8A779G0_CLK_S0D1_VIO),
 	DEF_MOD("tsn",		2723,	R8A779G0_CLK_S0D4_HSC),
+	DEF_MOD("dsc",		2819,	R8A779G0_CLK_VIOBUSD2),
 	DEF_MOD("ssiu",		2926,	R8A779G0_CLK_S0D6_PER),
 	DEF_MOD("ssi",		2927,	R8A779G0_CLK_S0D6_PER),
 };

-- 
2.43.0

[PATCH 2/5] dt-bindings: display: bridge: Document Renesas R-Car V4H DSC bindings

[Tomi Valkeinen]

From: Marek Vasut <marek.vasut+renesas@mailbox.org>

The Renesas DSC Display Stream Compression is a bridge embedded in the
Renesas R-Car V4H SoC. The bridge performs VESA DSC encoding of up to
8k or 400 Mpixel/s .

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
[tomi.valkeinen: fix the example]
Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
---
 .../bindings/display/bridge/renesas,dsc.yaml       | 96 ++++++++++++++++++++++
 1 file changed, 96 insertions(+)

diff --git a/Documentation/devicetree/bindings/display/bridge/renesas,dsc.yaml b/Documentation/devicetree/bindings/display/bridge/renesas,dsc.yaml
new file mode 100644
index 000000000000..91245beb67d7
--- /dev/null
+++ b/Documentation/devicetree/bindings/display/bridge/renesas,dsc.yaml
@@ -0,0 +1,96 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/display/bridge/renesas,dsc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Renesas R-Car DSC Display Stream Compression
+
+maintainers:
+  - Marek Vasut <marek.vasut+renesas@mailbox.org>
+
+description: |
+  This binding describes the VESA DSC Display Stream Compression encoder
+  embedded in the Renesas R-Car V4H SoC. The encoder supports all DSC1.1
+  encoding mechanisms, configurable bits-per-pixel, resolution up to 8k.
+
+properties:
+  compatible:
+    const: renesas,r8a779g0-dsc
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  power-domains:
+    maxItems: 1
+
+  resets:
+    maxItems: 1
+
+  ports:
+    $ref: /schemas/graph.yaml#/properties/ports
+
+    properties:
+      port@0:
+        $ref: /schemas/graph.yaml#/properties/port
+        description: R-Car DU input port
+
+      port@1:
+        $ref: /schemas/graph.yaml#/properties/port
+        description: R-Car DSI output port
+
+    required:
+      - port@0
+      - port@1
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - interrupts
+  - power-domains
+  - resets
+  - ports
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/r8a779g0-cpg-mssr.h>
+    #include <dt-bindings/interrupt-controller/arm-gic.h>
+    #include <dt-bindings/power/r8a779g0-sysc.h>
+
+    dsc@feb8d000 {
+        compatible = "renesas,r8a779g0-dsc";
+        reg = <0 0xfeb8d000 0 0x400>;
+        interrupts = <GIC_SPI 559 IRQ_TYPE_LEVEL_HIGH>;
+        clocks = <&cpg CPG_MOD 2819>;
+        power-domains = <&sysc R8A779G0_PD_ALWAYS_ON>;
+        resets = <&cpg 2819>;
+
+        ports {
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            port@0 {
+                reg = <0>;
+                dsc_in_dsi1: endpoint {
+                    remote-endpoint = <&du_out_dsi1>;
+                };
+            };
+
+            port@1 {
+                reg = <1>;
+                dsc_out_dsi1: endpoint {
+                    remote-endpoint = <&dsi1_in>;
+                };
+            };
+        };
+    };
+...

-- 
2.43.0

Re: [PATCH 2/5] dt-bindings: display: bridge: Document Renesas R-Car V4H DSC bindings

[Rob Herring (Arm)]

On Thu, 14 May 2026 15:24:54 +0300, Tomi Valkeinen wrote:
> From: Marek Vasut <marek.vasut+renesas@mailbox.org>
> 
> The Renesas DSC Display Stream Compression is a bridge embedded in the
> Renesas R-Car V4H SoC. The bridge performs VESA DSC encoding of up to
> 8k or 400 Mpixel/s .
> 
> Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
> [tomi.valkeinen: fix the example]
> Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
> ---
>  .../bindings/display/bridge/renesas,dsc.yaml       | 96 ++++++++++++++++++++++
>  1 file changed, 96 insertions(+)
> 

My bot found errors running 'make dt_binding_check' on your patch:

yamllint warnings/errors:

dtschema/dtc warnings/errors:
/builds/robherring/dt-review-ci/linux/Documentation/devicetree/bindings/display/bridge/renesas,dsc.example.dtb: dsc@feb8d000 (renesas,r8a779g0-dsc): reg: [[0, 4273524736], [0, 1024]] is too long
	from schema $id: http://devicetree.org/schemas/display/bridge/renesas,dsc.yaml

doc reference errors (make refcheckdocs):

See https://patchwork.kernel.org/project/devicetree/patch/20260514-rcar-du-dsc-v1-2-d65f7a9e9841@ideasonboard.com

The base for the series is generally the latest rc1. A different dependency
should be noted in *this* patch.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit after running the above command yourself. Note
that DT_SCHEMA_FILES can be set to your schema file to speed up checking
your schema. However, it must be unset to test all examples with your schema.

Re: [PATCH 2/5] dt-bindings: display: bridge: Document Renesas R-Car V4H DSC bindings

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The device tree example will fail `dt_binding_check` because the `reg` property uses 4 cells without a parent node specifying `#address-cells = <2>` and `#size-cells = <2>`.
--

commit 6a7e60ed22b69bbc15e77243a1b4bdb0d60396df
Author: Marek Vasut <marek.vasut+renesas@mailbox.org>

dt-bindings: display: bridge: Document Renesas R-Car V4H DSC bindings

This commit adds the device tree binding documentation for the VESA DSC
Display Stream Compression encoder embedded in the Renesas R-Car V4H SoC.

> diff --git a/Documentation/devicetree/bindings/display/bridge/renesas,dsc.yaml b/Documentation/devicetree/bindings/display/bridge/renesas,dsc.yaml
> new file mode 100644
> index 0000000000000..91245beb67d7b
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/display/bridge/renesas,dsc.yaml
[ ... ]
> +examples:
> +  - |
> +    #include <dt-bindings/clock/r8a779g0-cpg-mssr.h>
> +    #include <dt-bindings/interrupt-controller/arm-gic.h>
> +    #include <dt-bindings/power/r8a779g0-sysc.h>
> +
> +    dsc@feb8d000 {
> +        compatible = "renesas,r8a779g0-dsc";
> +        reg = <0 0xfeb8d000 0 0x400>;

Does this introduce a regression during dt_binding_check? By default, the
schema tooling wraps examples in a root node with #address-cells = <1> and
#size-cells = <1>.

Because the reg property uses 4 cells, it will be parsed as two items, which
violates the maxItems: 1 constraint defined earlier in the binding. Wrapping
the example in a parent node that specifies #address-cells = <2> and
#size-cells = <2> should resolve this.

> +        interrupts = <GIC_SPI 559 IRQ_TYPE_LEVEL_HIGH>;
[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260514-rcar-du-dsc-v1-0-d65f7a9e9841@ideasonboard.com?part=2

[PATCH 3/5] drm/rcar-du: dsc: Add rudimentary Renesas R-Car V4H DSC driver

[Tomi Valkeinen]

From: Marek Vasut <marek.vasut+renesas@mailbox.org>

The Renesas DSC Display Stream Compression is a bridge embedded in the
Renesas R-Car V4H SoC. The bridge performs VESA DSC encoding of up to
8k or 400 Mpixel/s . Add rudimentary driver, which currently acts as a
pass-through bridge and allows DSI1 to be operational on R-Car V4H.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
[tomi.valkeinen: use bridge->next_bridge, minor changes]
Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
---
 drivers/gpu/drm/renesas/rcar-du/Kconfig    |  13 +++
 drivers/gpu/drm/renesas/rcar-du/Makefile   |   1 +
 drivers/gpu/drm/renesas/rcar-du/rcar_dsc.c | 163 +++++++++++++++++++++++++++++
 3 files changed, 177 insertions(+)

diff --git a/drivers/gpu/drm/renesas/rcar-du/Kconfig b/drivers/gpu/drm/renesas/rcar-du/Kconfig
index 840305fdeb49..a51f996d3537 100644
--- a/drivers/gpu/drm/renesas/rcar-du/Kconfig
+++ b/drivers/gpu/drm/renesas/rcar-du/Kconfig
@@ -33,6 +33,19 @@ config DRM_RCAR_DW_HDMI
 	help
 	  Enable support for R-Car Gen3 or RZ/G2 internal HDMI encoder.
 
+config DRM_RCAR_USE_DSC
+	bool "R-Car DU DSC Encoder Support"
+	depends on DRM_BRIDGE && OF
+	depends on DRM_RCAR_DU || COMPILE_TEST
+	default DRM_RCAR_DU
+	help
+	  Enable support for the R-Car Display Unit embedded DSC encoder.
+
+config DRM_RCAR_DSC
+	def_tristate DRM_RCAR_DU
+	depends on DRM_RCAR_USE_DSC
+	select RESET_CONTROLLER
+
 config DRM_RCAR_USE_LVDS
 	bool "R-Car DU LVDS Encoder Support"
 	depends on DRM_BRIDGE && OF
diff --git a/drivers/gpu/drm/renesas/rcar-du/Makefile b/drivers/gpu/drm/renesas/rcar-du/Makefile
index 6f132325c8b7..cc27b2265d94 100644
--- a/drivers/gpu/drm/renesas/rcar-du/Makefile
+++ b/drivers/gpu/drm/renesas/rcar-du/Makefile
@@ -12,5 +12,6 @@ rcar-du-drm-$(CONFIG_DRM_RCAR_WRITEBACK) += rcar_du_writeback.o
 obj-$(CONFIG_DRM_RCAR_CMM)		+= rcar_cmm.o
 obj-$(CONFIG_DRM_RCAR_DU)		+= rcar-du-drm.o
 obj-$(CONFIG_DRM_RCAR_DW_HDMI)		+= rcar_dw_hdmi.o
+obj-$(CONFIG_DRM_RCAR_DSC)		+= rcar_dsc.o
 obj-$(CONFIG_DRM_RCAR_LVDS)		+= rcar_lvds.o
 obj-$(CONFIG_DRM_RCAR_MIPI_DSI)		+= rcar_mipi_dsi.o
diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_dsc.c b/drivers/gpu/drm/renesas/rcar-du/rcar_dsc.c
new file mode 100644
index 000000000000..2ab5a4bb099c
--- /dev/null
+++ b/drivers/gpu/drm/renesas/rcar-du/rcar_dsc.c
@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * R-Car DSC Encoder
+ *
+ * Copyright (C) 2025 Marek Vasut <marek.vasut+renesas@mailbox.org>
+ * Copyright (C) 2025 Renesas Electronics Corporation
+ */
+
+#include <linux/clk.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_graph.h>
+#include <linux/platform_device.h>
+#include <linux/reset.h>
+
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_bridge.h>
+#include <drm/drm_of.h>
+
+struct rcar_dsc {
+	struct drm_bridge bridge;
+
+	struct device *dev;
+	void __iomem *mmio;
+	struct clk *clk;
+	struct reset_control *rst;
+};
+
+static inline struct rcar_dsc *bridge_to_rcar_dsc(struct drm_bridge *bridge)
+{
+	return container_of(bridge, struct rcar_dsc, bridge);
+}
+
+/* -----------------------------------------------------------------------------
+ * Bridge
+ */
+
+static int rcar_dsc_attach(struct drm_bridge *bridge,
+			   struct drm_encoder *encoder,
+			   enum drm_bridge_attach_flags flags)
+{
+	struct rcar_dsc *dsc = bridge_to_rcar_dsc(bridge);
+
+	if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR))
+		return -EINVAL;
+
+	return drm_bridge_attach(encoder, dsc->bridge.next_bridge, bridge,
+				 DRM_BRIDGE_ATTACH_NO_CONNECTOR);
+}
+
+static void rcar_dsc_atomic_enable(struct drm_bridge *bridge,
+				   struct drm_atomic_state *state)
+{
+	struct rcar_dsc *dsc = bridge_to_rcar_dsc(bridge);
+
+	WARN_ON(clk_prepare_enable(dsc->clk));
+	WARN_ON(reset_control_deassert(dsc->rst));
+}
+
+static void rcar_dsc_atomic_disable(struct drm_bridge *bridge,
+				    struct drm_atomic_state *state)
+{
+	struct rcar_dsc *dsc = bridge_to_rcar_dsc(bridge);
+
+	reset_control_assert(dsc->rst);
+	clk_disable_unprepare(dsc->clk);
+}
+
+static enum drm_mode_status
+rcar_dsc_bridge_mode_valid(struct drm_bridge *bridge,
+			   const struct drm_display_info *info,
+			   const struct drm_display_mode *mode)
+{
+	if (mode->hdisplay < 320 || mode->hdisplay > 8190)
+		return MODE_BAD_HVALUE;
+
+	if (mode->vdisplay < 160 || mode->vdisplay > 8190)
+		return MODE_BAD_VVALUE;
+
+	if (mode->clock > 400000) /* Really 400 Mpixel/s */
+		return MODE_CLOCK_HIGH;
+
+	return MODE_OK;
+}
+
+static const struct drm_bridge_funcs rcar_dsc_bridge_ops = {
+	.attach = rcar_dsc_attach,
+	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
+	.atomic_reset = drm_atomic_helper_bridge_reset,
+	.atomic_enable = rcar_dsc_atomic_enable,
+	.atomic_disable = rcar_dsc_atomic_disable,
+	.mode_valid = rcar_dsc_bridge_mode_valid,
+};
+
+/* -----------------------------------------------------------------------------
+ * Probe & Remove
+ */
+
+static int rcar_dsc_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device_node *remote;
+	struct rcar_dsc *dsc;
+
+	dsc = devm_drm_bridge_alloc(dev, struct rcar_dsc, bridge,
+				    &rcar_dsc_bridge_ops);
+	if (IS_ERR(dsc))
+		return PTR_ERR(dsc);
+
+	platform_set_drvdata(pdev, dsc);
+
+	dsc->dev = &pdev->dev;
+
+	/* Acquire resources. */
+	dsc->mmio = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(dsc->mmio))
+		return PTR_ERR(dsc->mmio);
+
+	dsc->clk = devm_clk_get(dev, NULL);
+	if (IS_ERR(dsc->clk))
+		return dev_err_probe(dev, PTR_ERR(dsc->clk),
+				     "Failed to get CPG clock\n");
+
+	dsc->rst = devm_reset_control_get(dev, NULL);
+	if (IS_ERR(dsc->rst))
+		return dev_err_probe(dev, PTR_ERR(dsc->rst),
+				     "Failed to get CPG reset\n");
+
+	remote = of_graph_get_remote_node(dev->of_node, 1, 0);
+	if (!remote)
+		return -EINVAL;
+
+	dsc->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
+	of_node_put(remote);
+	if (!dsc->bridge.next_bridge)
+		return -EPROBE_DEFER;
+
+	dsc->bridge.of_node = dev->of_node;
+
+	return devm_drm_bridge_add(dev, &dsc->bridge);
+}
+
+static const struct of_device_id rcar_dsc_of_table[] = {
+	{ .compatible = "renesas,r8a779g0-dsc" },
+	{}
+};
+
+MODULE_DEVICE_TABLE(of, rcar_dsc_of_table);
+
+static struct platform_driver rcar_dsc_platform_driver = {
+	.probe          = rcar_dsc_probe,
+	.driver         = {
+		.name   = "rcar-dsc",
+		.of_match_table = rcar_dsc_of_table,
+	},
+};
+
+module_platform_driver(rcar_dsc_platform_driver);
+
+MODULE_DESCRIPTION("Renesas R-Car DSC Encoder Driver");
+MODULE_LICENSE("GPL");

-- 
2.43.0

Re: [PATCH 3/5] drm/rcar-du: dsc: Add rudimentary Renesas R-Car V4H DSC driver

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider:
- [High] Resource leak of the `next_bridge` reference on probe failure and driver unbind.
- [Medium] Kconfig logic error prevents the driver from being compiled under `COMPILE_TEST` when `DRM_RCAR_DU` is disabled.
- [Medium] Unbalanced clock disable and reset assertion if initialization fails in `rcar_dsc_atomic_enable()`.
- [Low] Usage of the deprecated `devm_reset_control_get()` API.
--

commit f5db250d6f577d9fcb67af0530df62ba814ec079
Author: Marek Vasut <marek.vasut+renesas@mailbox.org>
drm/rcar-du: dsc: Add rudimentary Renesas R-Car V4H DSC driver

This commit adds a rudimentary VESA DSC encoder driver for the R-Car V4H SoC,
which acts as a pass-through bridge and allows DSI1 to be operational.

> diff --git a/drivers/gpu/drm/renesas/rcar-du/Kconfig b/drivers/gpu/drm/renesas/rcar-du/Kconfig
> index 840305fdeb49a..a51f996d35375 100644
> --- a/drivers/gpu/drm/renesas/rcar-du/Kconfig
> +++ b/drivers/gpu/drm/renesas/rcar-du/Kconfig

[ ... ]

> @@ -33,6 +33,19 @@ config DRM_RCAR_DW_HDMI
>  	help
>  	  Enable support for R-Car Gen3 or RZ/G2 internal HDMI encoder.
>  
> +config DRM_RCAR_USE_DSC
> +	bool "R-Car DU DSC Encoder Support"
> +	depends on DRM_BRIDGE && OF
> +	depends on DRM_RCAR_DU || COMPILE_TEST
> +	default DRM_RCAR_DU
> +	help
> +	  Enable support for the R-Car Display Unit embedded DSC encoder.
> +
> +config DRM_RCAR_DSC
> +	def_tristate DRM_RCAR_DU

Because DRM_RCAR_DSC is a hidden config with def_tristate DRM_RCAR_DU, will
it always evaluate to 'n' if DRM_RCAR_DU is disabled, even when COMPILE_TEST
is enabled through DRM_RCAR_USE_DSC?

This seems like it would prevent the driver from actually being compiled under
COMPILE_TEST when the main DU driver is not selected.

> +	depends on DRM_RCAR_USE_DSC
> +	select RESET_CONTROLLER

[ ... ]

> diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_dsc.c b/drivers/gpu/drm/renesas/rcar-du/rcar_dsc.c
> new file mode 100644
> index 0000000000000..2ab5a4bb099c3
> --- /dev/null
> +++ b/drivers/gpu/drm/renesas/rcar-du/rcar_dsc.c

[ ... ]

> +static void rcar_dsc_atomic_enable(struct drm_bridge *bridge,
> +				   struct drm_atomic_state *state)
> +{
> +	struct rcar_dsc *dsc = bridge_to_rcar_dsc(bridge);
> +
> +	WARN_ON(clk_prepare_enable(dsc->clk));
> +	WARN_ON(reset_control_deassert(dsc->rst));
> +}
> +
> +static void rcar_dsc_atomic_disable(struct drm_bridge *bridge,
> +				    struct drm_atomic_state *state)
> +{
> +	struct rcar_dsc *dsc = bridge_to_rcar_dsc(bridge);
> +
> +	reset_control_assert(dsc->rst);
> +	clk_disable_unprepare(dsc->clk);

If clk_prepare_enable() fails in rcar_dsc_atomic_enable(), it returns an error
code but execution proceeds since the function returns void.

Will the unconditional call to clk_disable_unprepare() here lead to
unbalanced clock operations and trigger underflow warnings in the clock
framework?

[ ... ]

> +	dsc->clk = devm_clk_get(dev, NULL);
> +	if (IS_ERR(dsc->clk))
> +		return dev_err_probe(dev, PTR_ERR(dsc->clk),
> +				     "Failed to get CPG clock\n");
> +
> +	dsc->rst = devm_reset_control_get(dev, NULL);

This isn't a bug, but devm_reset_control_get() is documented as a deprecated
transition wrapper in <linux/reset.h>. Should this use
devm_reset_control_get_exclusive() instead?

> +	if (IS_ERR(dsc->rst))
> +		return dev_err_probe(dev, PTR_ERR(dsc->rst),
> +				     "Failed to get CPG reset\n");
> +
> +	remote = of_graph_get_remote_node(dev->of_node, 1, 0);
> +	if (!remote)
> +		return -EINVAL;
> +
> +	dsc->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
> +	of_node_put(remote);
> +	if (!dsc->bridge.next_bridge)
> +		return -EPROBE_DEFER;
> +
> +	dsc->bridge.of_node = dev->of_node;
> +
> +	return devm_drm_bridge_add(dev, &dsc->bridge);
> +}

of_drm_find_and_get_bridge() intentionally increments the module and device
reference counts for the returned bridge.

If devm_drm_bridge_add() fails, does this leak the reference to
next_bridge?

Also, since the driver lacks a .remove callback or a devm cleanup action, is
the reference permanently leaked when the driver is unbound?

Could this use the managed devm_drm_of_get_bridge() API to ensure proper
lifecycle management?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260514-rcar-du-dsc-v1-0-d65f7a9e9841@ideasonboard.com?part=3

[PATCH 4/5] drm/rcar-du: dsi: Support DSC in the pipeline

[Tomi Valkeinen]

Enabling DSI clocks on rcar-du needs some tricks as the DU dot clock is
provided by the DSI. Thus, we call rcar_mipi_dsi_pclk_enable() from the
crtc, when enabling the crtc.

With DSC (added in upcoming patch) in the pipeline, between the DU and
the DSI, the above call path is broken as the crtc tries to call
rcar_mipi_dsi_pclk_enable() on the DSC.

Adjust the rcar_mipi_dsi_pclk_enable() so that it detects the DSC, and
in that case gets the next bridge from the DSC, which is the DSI.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
---
 drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c | 36 +++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
index 4ef2e3c129ed..085e229bcb0b 100644
--- a/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
+++ b/drivers/gpu/drm/renesas/rcar-du/rcar_mipi_dsi.c
@@ -88,6 +88,8 @@ struct dsi_setup_info {
 	const struct dsi_clk_config *clkset;
 };
 
+static const struct drm_bridge_funcs rcar_mipi_dsi_bridge_ops;
+
 static inline struct rcar_mipi_dsi *
 bridge_to_rcar_mipi_dsi(struct drm_bridge *bridge)
 {
@@ -844,15 +846,39 @@ static void rcar_mipi_dsi_atomic_disable(struct drm_bridge *bridge,
 	rcar_mipi_dsi_stop_video(dsi);
 }
 
+/*
+ * We need to skip the DSC bridge when we have DSC in between the DU and
+ * the DSI. We detect the DSI bridge via bridge->funcs, and assume the
+ * next_bridge is the DSI bridge. If this is not the case, the DT data
+ * is wrong (so it shouldn't really happen).
+ */
+static struct drm_bridge *
+rcar_mipi_dsi_resolve_bridge(struct drm_bridge *bridge)
+{
+	if (bridge->funcs != &rcar_mipi_dsi_bridge_ops)
+		bridge = bridge->next_bridge;
+
+	if (!bridge || bridge->funcs != &rcar_mipi_dsi_bridge_ops)
+		return NULL;
+
+	return bridge;
+}
+
 void rcar_mipi_dsi_pclk_enable(struct drm_bridge *bridge,
 			       struct drm_atomic_state *state)
 {
-	struct rcar_mipi_dsi *dsi = bridge_to_rcar_mipi_dsi(bridge);
 	const struct drm_display_mode *mode;
 	struct drm_connector *connector;
+	struct rcar_mipi_dsi *dsi;
 	struct drm_crtc *crtc;
 	int ret;
 
+	bridge = rcar_mipi_dsi_resolve_bridge(bridge);
+	if (WARN_ON(!bridge))
+		return;
+
+	dsi = bridge_to_rcar_mipi_dsi(bridge);
+
 	connector = drm_atomic_get_new_connector_for_encoder(state,
 							     bridge->encoder);
 	crtc = drm_atomic_get_new_connector_state(state, connector)->crtc;
@@ -885,7 +911,13 @@ EXPORT_SYMBOL_GPL(rcar_mipi_dsi_pclk_enable);
 
 void rcar_mipi_dsi_pclk_disable(struct drm_bridge *bridge)
 {
-	struct rcar_mipi_dsi *dsi = bridge_to_rcar_mipi_dsi(bridge);
+	struct rcar_mipi_dsi *dsi;
+
+	bridge = rcar_mipi_dsi_resolve_bridge(bridge);
+	if (WARN_ON(!bridge))
+		return;
+
+	dsi = bridge_to_rcar_mipi_dsi(bridge);
 
 	rcar_mipi_dsi_shutdown(dsi);
 	rcar_mipi_dsi_clk_disable(dsi);

-- 
2.43.0

[PATCH 5/5] arm64: dts: renesas: Add Renesas R-Car V4H DSC

[Tomi Valkeinen]

From: Marek Vasut <marek.vasut+renesas@mailbox.org>

The Renesas DSC Display Stream Compression is a bridge embedded in the
Renesas R-Car V4H SoC. The bridge is placed between DU and DSI1 units.
Describe the bridge in DT and enable it on Retronix Sparrow Hawk board
to keep DSI1 operational on this board.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
---
 arch/arm64/boot/dts/renesas/r8a779g0.dtsi          | 31 +++++++++++++++++++++-
 .../boot/dts/renesas/r8a779g3-sparrow-hawk.dts     |  5 ++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/boot/dts/renesas/r8a779g0.dtsi b/arch/arm64/boot/dts/renesas/r8a779g0.dtsi
index 82a7278836e5..52a6176f9fd0 100644
--- a/arch/arm64/boot/dts/renesas/r8a779g0.dtsi
+++ b/arch/arm64/boot/dts/renesas/r8a779g0.dtsi
@@ -2298,6 +2298,35 @@ du_out_dsi0: endpoint {
 				port@1 {
 					reg = <1>;
 					du_out_dsi1: endpoint {
+						remote-endpoint = <&dsc_in_dsi1>;
+					};
+				};
+			};
+		};
+
+		dsc: dsc@feb8d000 {
+			compatible = "renesas,r8a779g0-dsc";
+			reg = <0 0xfeb8d000 0 0x400>;
+			interrupts = <GIC_SPI 559 IRQ_TYPE_LEVEL_HIGH>;
+			clocks = <&cpg CPG_MOD 2819>;
+			power-domains = <&sysc R8A779G0_PD_ALWAYS_ON>;
+			resets = <&cpg 2819>;
+			status = "disabled";
+
+			ports {
+				#address-cells = <1>;
+				#size-cells = <0>;
+
+				port@0 {
+					reg = <0>;
+					dsc_in_dsi1: endpoint {
+						remote-endpoint = <&du_out_dsi1>;
+					};
+				};
+
+				port@1 {
+					reg = <1>;
+					dsc_out_dsi1: endpoint {
 						remote-endpoint = <&dsi1_in>;
 					};
 				};
@@ -2534,7 +2563,7 @@ ports {
 				port@0 {
 					reg = <0>;
 					dsi1_in: endpoint {
-						remote-endpoint = <&du_out_dsi1>;
+						remote-endpoint = <&dsc_out_dsi1>;
 					};
 				};
 
diff --git a/arch/arm64/boot/dts/renesas/r8a779g3-sparrow-hawk.dts b/arch/arm64/boot/dts/renesas/r8a779g3-sparrow-hawk.dts
index 812b133cf29e..f418998c6b05 100644
--- a/arch/arm64/boot/dts/renesas/r8a779g3-sparrow-hawk.dts
+++ b/arch/arm64/boot/dts/renesas/r8a779g3-sparrow-hawk.dts
@@ -288,6 +288,11 @@ channel4 {
 	};
 };
 
+/* Page 27 / DSI to Display */
+&dsc {
+	status = "okay";
+};
+
 /* Page 27 / DSI to Display */
 &dsi1 {
 	status = "okay";

-- 
2.43.0