Re: [PATCH v2 06/10] drm/bridge: dw-hdmi: warn on unsupported attach combination
From: Damon Ding
Date: Thu Apr 02 2026 - 05:17:54 EST
Hi Luca,
On 3/31/2026 3:25 AM, Luca Ceresoli wrote:
dw-hdmi can operate in two different modes, depending on the platform data
as set by the driver:
A. hdmi->plat_data->output_port = 0:
the HDMI output (port@1) in device tree is not used
B. hdmi->plat_data->output_port = 1:
the HDMI output (port@1) is parsed to find the next bridge
Only case B is supported when the DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is
passed to the attach callback. Emit a warning when this is violated. Also
return -EINVAL which would be returned by drm_bridge_attach() right after
anyway.
Reviewed-by: Liu Ying <victor.liu@xxxxxxx>
Tested-by: Martyn Welch <martyn.welch@xxxxxxxxxxxxx>
Tested-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx> # TQMa8MPxL/MBa8MPxL
Signed-off-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx>
---
Note: Returning when the warning triggers does not change the functional
behaviour of this function. It is not strictly necessary in this patch but
it will have to be done anyway in the following patch.
---
drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index 0296e110ce65..ab1a6a8783cd 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -2910,6 +2910,10 @@ static int dw_hdmi_bridge_attach(struct drm_bridge *bridge,
{
struct dw_hdmi *hdmi = bridge->driver_private;
+ /* DRM_BRIDGE_ATTACH_NO_CONNECTOR requires a remote-endpoint to the next bridge */
+ if (WARN_ON((flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) && !hdmi->plat_data->output_port))
+ return -EINVAL;
+
if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
return drm_bridge_attach(encoder, hdmi->bridge.next_bridge,
bridge, flags);
Since many older Rockchip platforms (RK3288, RK3399, etc.) lack a hdmi-connector node linked to the HDMI DT node, which corresponds to case A. Could we relax this restriction and treat cases where DRM_BRIDGE_ATTACH_NO_CONNECTOR is set but hdmi->plat_data->output_port = 0 as a new case C?
For Rockchip platforms, the HDMI driver invokes dw_hdmi_bind() to attach the Synopsys bridge. This sequence differs from that on the XNP platform, but is similar to the Allwinner implementation.
If we treat the case where DRM_BRIDGE_ATTACH_NO_CONNECTOR is set and hdmi->plat_data->output_port = 0 as -EINVAL, I will have to modify the HDMI DT configuration for all Rockchip platforms when adapting to the bridge-connector framework.
The patch that adapts to the bridge-connector framework and has been verified OK on RK3399 is attached.
Best regards,
Damon
diff --git a/arch/arm64/boot/dts/rockchip/rk3399-evb-ind.dts b/arch/arm64/boot/dts/rockchip/rk3399-evb-ind.dts
index 70aee1ab904c..5a78e741f113 100644
--- a/arch/arm64/boot/dts/rockchip/rk3399-evb-ind.dts
+++ b/arch/arm64/boot/dts/rockchip/rk3399-evb-ind.dts
@@ -17,6 +17,7 @@ aliases {
chosen {
stdout-path = "serial2:1500000n8";
+ bootargs = "root=PARTUUID=614e0000-0000 rootwait";
};
vcc5v0_sys: regulator-vcc5v0-sys {
diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index ada45e8b3e2c..0e97e183a8b3 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -2914,7 +2914,7 @@ static int dw_hdmi_bridge_attach(struct drm_bridge *bridge,
/* DRM_BRIDGE_ATTACH_NO_CONNECTOR requires a remote-endpoint to the next bridge */
if (WARN_ON((flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) && !hdmi->plat_data->output_port))
- return -EINVAL;
+ return 0;
if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
struct device_node *remote __free(device_node) =
@@ -3628,7 +3628,7 @@ struct dw_hdmi *dw_hdmi_bind(struct platform_device *pdev,
if (IS_ERR(hdmi))
return hdmi;
- ret = drm_bridge_attach(encoder, &hdmi->bridge, NULL, 0);
+ ret = drm_bridge_attach(encoder, &hdmi->bridge, NULL, DRM_BRIDGE_ATTACH_NO_CONNECTOR);
if (ret) {
dw_hdmi_remove(hdmi);
return ERR_PTR(ret);
diff --git a/drivers/gpu/drm/rockchip/Kconfig b/drivers/gpu/drm/rockchip/Kconfig
index e7f49fe845ea..69b832d0c8c4 100644
--- a/drivers/gpu/drm/rockchip/Kconfig
+++ b/drivers/gpu/drm/rockchip/Kconfig
@@ -76,6 +76,7 @@ config ROCKCHIP_DW_DP
config ROCKCHIP_DW_HDMI
bool "Rockchip specific extensions for Synopsys DW HDMI"
+ select DRM_BRIDGE_CONNECTOR
help
This selects support for Rockchip SoC specific extensions
for the Synopsys DesignWare HDMI driver. If you want to
diff --git a/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c b/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
index 0dc1eb5d2ae3..174a10c1d7c2 100644
--- a/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
+++ b/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
@@ -13,6 +13,7 @@
#include <linux/regulator/consumer.h>
#include <drm/bridge/dw_hdmi.h>
+#include <drm/drm_bridge_connector.h>
#include <drm/drm_edid.h>
#include <drm/drm_of.h>
#include <drm/drm_probe_helper.h>
@@ -542,6 +543,7 @@ static int dw_hdmi_rockchip_bind(struct device *dev, struct device *master,
struct drm_device *drm = data;
struct drm_encoder *encoder;
struct rockchip_hdmi *hdmi;
+ struct drm_connector *connector;
int ret;
if (!pdev->dev.of_node)
@@ -619,7 +621,14 @@ static int dw_hdmi_rockchip_bind(struct device *dev, struct device *master,
goto err_bind;
}
- return 0;
+ connector = drm_bridge_connector_init(drm, encoder);
+ if (IS_ERR(connector)) {
+ ret = PTR_ERR(connector);
+ dev_err(hdmi->dev, "Failed to initialize bridge_connector\n");
+ goto err_bind;
+ }
+
+ return drm_connector_attach_encoder(connector, encoder);
err_bind:
drm_encoder_cleanup(encoder);