Re: [PATCH 7/8] drm/bridge: imx8mp-hdmi-tx: add an hdmi-connector when missing using a DT overlay at boot time

Liu Ying
2026-03-26T08:14:52Z

Hi Luca,

On Fri, Mar 20, 2026 at 11:46:18AM +0100, Luca Ceresoli wrote:
> The imx8mp-hdmi-tx one of many drivers based on dw-hdmi. dw-hdmi in turn
> 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 [0]
>
> B. hdmi->plat_data->output_port = 1:
> the HDMI output (port@1) is parsed to find the next bridge
>
> The imx8mp-hdmi-tx driver falls in case A. This implies next_bridge will
> always be NULL, and so dw_hdmi_bridge_attach() [1] will always fail if
> called with the DRM_BRIDGE_ATTACH_NO_CONNECTOR flag.
>
> In fact case A assumes that DRM_BRIDGE_ATTACH_NO_CONNECTOR is not set and
> in that case it adds the connector programmatically at bridge attach time.
>
> Support for DRM_BRIDGE_ATTACH_NO_CONNECTOR is implemented by dw-hdmi.c in
> case B. So, in preparation to support DRM_BRIDGE_ATTACH_NO_CONNECTOR in
> imx8mp-hdmi-tx, move to case B by setting hdmi->plat_data->output_port = 1.
>
> However this change requires that port@1 is connected to a "next
> bridge" DT node, typically the HDMI connector, because dw-hdmi won't add
> the connector when using DRM_BRIDGE_ATTACH_NO_CONNECTOR.
>
> Many dts files for imx8mp-based boards in the kernel have such a connector
> described and linked to port@1, so a connector is added by the
> display-connector driver along with a bridge wrapping it. Sadly some of

Hmm, display-connector driver is a bridge driver so it cannot add a connector.
I assume that you mean a connector will be added by the bridge connector
driver.

> those dts files don't have the connector described. Adding it would solve
> the problem easily, but this would break existing devices which do not
> update the dtb when upgrading to a newer kernel.
>
> To preserve backward compatibility for such devices, introduce a module
> adding the hdmi-connector node to the live device tree at init time. This
> allows the dw-hdmi code to find the next bridge (the one wrapping the
> hdmi-connector) and let the pipeline work as before.
>
> [0] https://elixir.bootlin.com/linux/v7.0-rc1/source/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c#L3310
> [1] https://elixir.bootlin.com/linux/v7.0-rc1/source/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c#L2907
>
> Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
>
> ---
>
> This patch is inspired by commit 0ff223d99147 ("drm/tilcdc: Convert legacy
> panel binding via DT overlay at boot time")
> ---
> drivers/gpu/drm/bridge/imx/Kconfig | 17 ++++++
> drivers/gpu/drm/bridge/imx/Makefile | 2 +
> .../bridge/imx/imx8mp-hdmi-tx-connector-fixup.c | 60 ++++++++++++++++++++++
> .../bridge/imx/imx8mp-hdmi-tx-connector-fixup.dtso | 38 ++++++++++++++
> drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c | 1 +
> 5 files changed, 118 insertions(+)
>
> diff --git a/drivers/gpu/drm/bridge/imx/Kconfig b/drivers/gpu/drm/bridge/imx/Kconfig
> index b9028a5e5a06..b9ce140a93dc 100644
> --- a/drivers/gpu/drm/bridge/imx/Kconfig
> +++ b/drivers/gpu/drm/bridge/imx/Kconfig
> @@ -25,6 +25,23 @@ config DRM_IMX8MP_DW_HDMI_BRIDGE
> Choose this to enable support for the internal HDMI encoder found
> on the i.MX8MP SoC.
>
> +config DRM_IMX8MP_DW_HDMI_BRIDGE_CONNECTOR_FIXUP
> + bool "Support device tree blobs without an hdmi-connector node"
> + default y

depends on DRM_IMX_LCDIF ?

> + depends on DRM_IMX8MP_DW_HDMI_BRIDGE
> + depends on OF
> + select OF_OVERLAY
> + select DRM_DISPLAY_CONNECTOR
> + help
> + Modifies at early boot the live device tree of boards using the
> + i.MX8MP fsl,imx8mp-hdmi-tx adding a hdmi-connector node linked to
> + the htmi-tx. This is needed to support bridge-connector usage in

s/htmi/hdmi/

> + the i.MX8MP LCDIF driver.
> +
> + You need this if you use the i.MX8MP HDMI output and your board
> + device tree file does not have an hdmi-connector node connected
> + to it.
> +
> config DRM_IMX8MP_HDMI_PAI
> tristate "Freescale i.MX8MP HDMI PAI bridge support"
> depends on OF
> diff --git a/drivers/gpu/drm/bridge/imx/Makefile b/drivers/gpu/drm/bridge/imx/Makefile
> index 8d01fda25451..84499fe2e444 100644
> --- a/drivers/gpu/drm/bridge/imx/Makefile
> +++ b/drivers/gpu/drm/bridge/imx/Makefile
> @@ -1,6 +1,8 @@
> obj-$(CONFIG_DRM_IMX_LDB_HELPER) += imx-ldb-helper.o
> obj-$(CONFIG_DRM_IMX_LEGACY_BRIDGE) += imx-legacy-bridge.o
> obj-$(CONFIG_DRM_IMX8MP_DW_HDMI_BRIDGE) += imx8mp-hdmi-tx.o
> +obj-$(CONFIG_DRM_IMX8MP_DW_HDMI_BRIDGE_CONNECTOR_FIXUP) += imx8mp-hdmi-tx-connector-fixup.o \
> + imx8mp-hdmi-tx-connector-fixup.dtbo.o
> obj-$(CONFIG_DRM_IMX8MP_HDMI_PAI) += imx8mp-hdmi-pai.o
> obj-$(CONFIG_DRM_IMX8MP_HDMI_PVI) += imx8mp-hdmi-pvi.o
> obj-$(CONFIG_DRM_IMX8QM_LDB) += imx8qm-ldb.o
> diff --git a/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.c b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.c
> new file mode 100644
> index 000000000000..8c423b9bfa50
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.c
> @@ -0,0 +1,60 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Add an hdmi-connector node to boards using the imx8mp hdmi_tx which
> + * don't have one. This is needed for the i.MX LCDIF to work with
> + * DRM_BRIDGE_ATTACH_NO_CONNECTOR.
> + *
> + * Copyright (C) 2026 GE HealthCare
> + * Author: Luca Ceresoli <luca.ceresoli@bootlin.com>
> + */
> +
> +#include <linux/kernel.h>

Unneeded?

> +#include <linux/of.h>
> +#include <linux/of_fdt.h>
> +#include <linux/slab.h>

Unneeded?

> +
> +/* Embedded dtbo symbols created by cmd_wrap_S_dtb in scripts/Makefile.dtbs */
> +extern char __dtbo_imx8mp_hdmi_tx_connector_fixup_begin[];
> +extern char __dtbo_imx8mp_hdmi_tx_connector_fixup_end[];
> +
> +static int __init imx8mp_hdmi_tx_connector_fixup_init(void)
> +{
> + struct device_node *hdmi_tx __free(device_node) = NULL;

Include linux/cleanup.h as __free() is used.

> + struct device_node *endpoint __free(device_node) = NULL;
> + struct device_node *hdmi_conn __free(device_node) = NULL;
> + void *dtbo_start;
> + u32 dtbo_size;
> + int ovcs_id;
> + int err;
> +
> + hdmi_tx = of_find_node_by_path("/soc@0/bus@32c00000/hdmi@32fd8000");
> + if (!of_device_is_available(hdmi_tx))
> + return 0;
> +
> + /* If endpoint exists, assume an hdmi-connector exists already */
> + endpoint = of_find_node_by_path("/soc@0/bus@32c00000/hdmi@32fd8000/ports/port@1/endpoint");
> + if (endpoint)
> + return 0;
> +
> + dtbo_start = __dtbo_imx8mp_hdmi_tx_connector_fixup_begin;
> + dtbo_size = __dtbo_imx8mp_hdmi_tx_connector_fixup_end -
> + __dtbo_imx8mp_hdmi_tx_connector_fixup_begin;
> +
> + err = of_overlay_fdt_apply(dtbo_start, dtbo_size, &ovcs_id, NULL);
> + if (err)
> + return err;
> +
> + hdmi_conn = of_find_node_by_name(NULL, "fixup-hdmi-connector");

Do you really need to find the node, since the overlay was just applied?

> + if (!hdmi_conn) {
> + err = -ENODEV;
> + goto overlay_remove;

I'd just return -ENODEV and drop overlay_remove.

> + }
> +
> + return 0;
> +
> +overlay_remove:
> + of_overlay_remove(&ovcs_id);
> + return err;
> +}
> +
> +subsys_initcall(imx8mp_hdmi_tx_connector_fixup_init);
> diff --git a/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.dtso b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.dtso
> new file mode 100644
> index 000000000000..ee718ca1b11b
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.dtso
> @@ -0,0 +1,38 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * DTS overlay adding an hdmi-connector node to boards using the imx8mp hdmi_tx
> + *
> + * Copyright (C) 2026 GE HealthCare
> + * Author: Luca Ceresoli <luca.ceresoli@bootlin.com>
> + */
> +
> +/dts-v1/;
> +/plugin/;
> +
> +&{/} {

I see build warnings(W=1):
drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.dtso:25.8-37.4: Warning (unit_address_vs_reg): /fragment@0/__overlay__/soc@0: node has a unit name, but no reg or ranges property
drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.dtso:26.16-36.5: Warning (unit_address_vs_reg): /fragment@0/__overlay__/soc@0/bus@32c00000: node has a unit name, but no reg or ranges property
drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.dtso:27.18-35.6: Warning (unit_address_vs_reg): /fragment@0/__overlay__/soc@0/bus@32c00000/hdmi@32fd8000: node has a unit name, but no reg or ranges property
drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.dtso:29.13-33.8: Warning (unit_address_vs_reg): /fragment@0/__overlay__/soc@0/bus@32c00000/hdmi@32fd8000/ports/port@1: node has a unit name, but no reg or ranges property

Here is a patch to suppress them:

--- a/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.dtso
+++ b/drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx-connector-fixup.dtso
@@ -10,6 +10,9 @@
/plugin/;

&{/} {
+ #address-cells = <2>;
+ #size-cells = <2>;
+
fixup-hdmi-connector {
compatible = "hdmi-connector";
label = "HDMI";
@@ -23,10 +26,25 @@ fixup_hdmi_connector_in: endpoint {
};

soc@0 {
+ #address-cells = <1>;
+ #size-cells = <1>;
+ ranges = <0x0 0x0 0x0 0x3e000000>;
+
bus@32c00000 {
+ reg = <0x32c00000 0x400000>;
+ #address-cells = <1>;
+ #size-cells = <1>;
+
hdmi@32fd8000 {
+ reg = <0x32fd8000 0x7eff>;
+
ports {
+ #address-cells = <1>;
+ #size-cells = <0>;
+
port@1 {
+ reg = <1>;
+
hdmi_tx_out: endpoint {
remote-endpoint = <&fixup_hdmi_connector_in>;
};

> + fixup-hdmi-connector {
> + compatible = "hdmi-connector";
> + label = "HDMI";
> + type = "a";

What if a board uses another type?

--
Regards,
Liu Ying