Re: [PATCH v2 07/10] drm/bridge: dw-hdmi: move next_bridge lookup to attach time

Damon Ding
2026-03-31T07:59:50Z

On 3/31/2026 3:25 AM, Luca Ceresoli wrote:
> This driver looks up the next_bridge at probe time and stores it in
> hdmi->bridge.next_bridge, but only uses the stored value when attaching,
> and only in the DRM_BRIDGE_ATTACH_NO_CONNECTOR case.
>
> This will be problematic with an upcoming change, adding an hdmi-connector
> using a device tree overlay when not present. That change is in turn
> necessary to migrate the i.MX LCDIF driver to the bridge-connector.
>
> The problem is that, adding the hdmi-connector via an overlay, devlink
> considers hdmi-connector a consumer of the dw-hdmi device, generating a
> chicken-egg problem:
>
> * hdmi-connector probe won't be tried until dw-hdmi is probed (devlink)
> * dw-hdmi probe will defer until it finds the next_bridge (the
> hdmi-connector wrapper bridge)
>
> In preparation for those changes, move the next_bridge lookup from probe to
> attach, when it is actually used. This allows dw-hdmi to probe, so that the
> hdmi-connector can probe as well.
>
> Also avoid storing the pointer in hdmi->bridge.next_bridge: the value is
> computed when needed, thus a local variable is enough.
>
> Finally, this also allows to slightly improve the code by not doing any DT
> lookup in the !DRM_BRIDGE_ATTACH_NO_CONNECTOR case.
>
> Tested-by: Martyn Welch <martyn.welch@collabora.com>
> Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com> # TQMa8MPxL/MBa8MPxL
> Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
>
> ---
>
> Changes in v2:
> - Fix returned error codes
> - Added missing cleanup.h include
> ---
> drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 45 +++++++++++--------------------
> 1 file changed, 16 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> index ab1a6a8783cd..f4a1ebb79716 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> @@ -6,6 +6,8 @@
> * Copyright (C) 2011-2013 Freescale Semiconductor, Inc.
> * Copyright (C) 2010, Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> */
> +
> +#include <linux/cleanup.h>
> #include <linux/clk.h>
> #include <linux/delay.h>
> #include <linux/err.h>
> @@ -2914,9 +2916,20 @@ static int dw_hdmi_bridge_attach(struct drm_bridge *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);
> + if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR) {
> + struct device_node *remote __free(device_node) =
> + of_graph_get_remote_node(hdmi->dev->of_node,
> + hdmi->plat_data->output_port, -1);
> + if (!remote)
> + return -ENODEV;
> +
> + struct drm_bridge *next_bridge __free(drm_bridge_put) =
> + of_drm_find_and_get_bridge(remote);
> + if (!next_bridge)
> + return -EPROBE_DEFER;
> +
> + return drm_bridge_attach(encoder, next_bridge, bridge, flags);
> + }
>
> return dw_hdmi_connector_create(hdmi);
> }
> @@ -3307,28 +3320,6 @@ static void dw_hdmi_init_hw(struct dw_hdmi *hdmi)
> * Probe/remove API, used from platforms based on the DRM bridge API.
> */
>
> -static int dw_hdmi_parse_dt(struct dw_hdmi *hdmi)
> -{
> - struct device_node *remote;
> -
> - if (!hdmi->plat_data->output_port)
> - return 0;
> -
> -
> - remote = of_graph_get_remote_node(hdmi->dev->of_node,
> - hdmi->plat_data->output_port,
> - -1);
> - if (!remote)
> - return -ENODEV;
> -
> - hdmi->bridge.next_bridge = of_drm_find_and_get_bridge(remote);
> - of_node_put(remote);
> - if (!hdmi->bridge.next_bridge)
> - return -EPROBE_DEFER;
> -
> - return 0;
> -}
> -
> bool dw_hdmi_bus_fmt_is_420(struct dw_hdmi *hdmi)
> {
> return hdmi_bus_fmt_is_yuv420(hdmi->hdmi_data.enc_out_bus_format);
> @@ -3373,10 +3364,6 @@ struct dw_hdmi *dw_hdmi_probe(struct platform_device *pdev,
> mutex_init(&hdmi->cec_notifier_mutex);
> spin_lock_init(&hdmi->audio_lock);
>
> - ret = dw_hdmi_parse_dt(hdmi);
> - if (ret < 0)
> - return ERR_PTR(ret);
> -
> ddc_node = of_parse_phandle(np, "ddc-i2c-bus", 0);
> if (ddc_node) {
> hdmi->ddc = of_get_i2c_adapter_by_node(ddc_node);
>

Tested-by: Damon Ding <damon.ding@rock-chips.com> (on rk3399)

Best regards,
Damon