[PATCH v1] drm/bridge: ssd2825: Fix panel enable sequence

[PATCH v1] drm/bridge: ssd2825: Fix panel enable sequence

[Svyatoslav Ryhel]

Currently, in the case of a single bridge and a single panel, the DRM
framework calls panel prepare() > bridge pre_enable() > bridge enable() >
panel enable(). While this is fine for most cases, the SSD2825 requires
the last two steps to be swapped. There is no meaningful way to achieve
this using standard bridge chain configuration, so the bridge previously
called panel_enable() directly at the end of its pre_enable() hook to
gain fine-grained control over the sequence.

Commit 554d36acf5e0 ("drm/bridge: ssd2825: don't create a panel_bridge")
removed this call, resulting in a regression where display output is
missing because the panel enable function is now called after the bridge
completes its configuration.

Since panels are now automatically wrapped into the bridge framework,
invoke the next bridge's atomic enable directly, similar to how panel
enabling was handled previously.

This restores panel support on the LG Optimus 4X HD (P880) and
Optimus Vu (P895).

Fixes: 554d36acf5e0 ("drm/bridge: ssd2825: don't create a panel_bridge")
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
---
 drivers/gpu/drm/bridge/ssd2825.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/bridge/ssd2825.c b/drivers/gpu/drm/bridge/ssd2825.c
index 71877699dfab6..9216cee09115f 100644
--- a/drivers/gpu/drm/bridge/ssd2825.c
+++ b/drivers/gpu/drm/bridge/ssd2825.c
@@ -475,6 +475,7 @@ static void ssd2825_bridge_atomic_pre_enable(struct drm_bridge *bridge,
 					     struct drm_atomic_commit *state)
 {
 	struct ssd2825_priv *priv = bridge_to_ssd2825(bridge);
+	struct drm_bridge *next_bridge = priv->output.bridge;
 	struct mipi_dsi_device *dsi_dev = priv->output.dev;
 	const struct drm_crtc_state *crtc_state;
 	const struct drm_display_mode *mode;
@@ -569,6 +570,14 @@ static void ssd2825_bridge_atomic_pre_enable(struct drm_bridge *bridge,
 	/* Initial DSI configuration register set */
 	ssd2825_write_reg(priv, SSD2825_CONFIGURATION_REG, config);
 	ssd2825_write_reg(priv, SSD2825_VC_CTRL_REG, 0);
+
+	/*
+	 * The SSD2825 requires that the next bridge be enabled first;
+	 * otherwise, the SSD2825 cannot complete its configuration and
+	 * there will be no output.
+	 */
+	if (next_bridge->funcs && next_bridge->funcs->atomic_enable)
+		next_bridge->funcs->atomic_enable(next_bridge, state);
 }
 
 static void ssd2825_bridge_atomic_enable(struct drm_bridge *bridge,
-- 
2.53.0

Re: [PATCH v1] drm/bridge: ssd2825: Fix panel enable sequence

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] drm/bridge: ssd2825: duplicate atomic_enable() call on next_bridge
--

commit 1c5e404afec7538a0e06a870cc1167b8db336814
Author: Svyatoslav Ryhel <clamor95@gmail.com>

drm/bridge: ssd2825: Fix panel enable sequence

This commit invokes the next bridge's atomic_enable() callback directly at
the end of ssd2825_bridge_atomic_pre_enable() to restore panel output after
commit 554d36acf5e0 removed direct panel handling.

> diff --git a/drivers/gpu/drm/bridge/ssd2825.c b/drivers/gpu/drm/bridge/ssd2825.c
> index 71877699dfab6..9216cee09115f 100644
> --- a/drivers/gpu/drm/bridge/ssd2825.c
> +++ b/drivers/gpu/drm/bridge/ssd2825.c
> @@ -475,6 +475,7 @@ static void ssd2825_bridge_atomic_pre_enable(struct drm_bridge *bridge,
>  					     struct drm_atomic_commit *state)
>  {
>  	struct ssd2825_priv *priv = bridge_to_ssd2825(bridge);
> +	struct drm_bridge *next_bridge = priv->output.bridge;
>  	struct mipi_dsi_device *dsi_dev = priv->output.dev;
>  	const struct drm_crtc_state *crtc_state;
>  	const struct drm_display_mode *mode;
> @@ -569,6 +570,14 @@ static void ssd2825_bridge_atomic_pre_enable(struct drm_bridge *bridge,
>  	/* Initial DSI configuration register set */
>  	ssd2825_write_reg(priv, SSD2825_CONFIGURATION_REG, config);
>  	ssd2825_write_reg(priv, SSD2825_VC_CTRL_REG, 0);
> +
> +	/*
> +	 * The SSD2825 requires that the next bridge be enabled first;
> +	 * otherwise, the SSD2825 cannot complete its configuration and
> +	 * there will be no output.
> +	 */
> +	if (next_bridge->funcs && next_bridge->funcs->atomic_enable)
> +		next_bridge->funcs->atomic_enable(next_bridge, state);

[Severity: Medium]
Does calling next_bridge->funcs->atomic_enable() directly in
ssd2825_bridge_atomic_pre_enable() cause next_bridge->funcs->atomic_enable()
to be invoked twice on every modeset enable?

In drivers/gpu/drm/bridge/ssd2825.c, ssd2825_bridge_attach() attaches
priv->output.bridge to the encoder's bridge chain:

	return drm_bridge_attach(bridge->encoder, priv->output.bridge, bridge,
				 flags);

During an atomic modeset enable, drm_atomic_helper_commit_modeset_enables()
runs drm_atomic_bridge_chain_pre_enable(), which calls
ssd2825_bridge_atomic_pre_enable() and now invokes
next_bridge->funcs->atomic_enable() for the first time.

Immediately afterwards, drm_atomic_helper_commit_encoder_bridge_enable()
calls drm_atomic_bridge_chain_enable() in drivers/gpu/drm/drm_bridge.c:

	drm_for_each_bridge_in_chain_from(first_bridge, bridge)
		if (bridge->funcs->atomic_enable)
			bridge->funcs->atomic_enable(bridge, state);

This calls next_bridge->funcs->atomic_enable() a second time while
drm_atomic_bridge_chain_disable() only calls atomic_disable() once.

When next_bridge is a panel bridge, panel_bridge_atomic_enable() calls
drm_panel_enable() in drivers/gpu/drm/drm_panel.c, where the second call hits
the already-enabled check and emits a warning on every modeset:

	if (panel->enabled) {
		dev_warn(panel->dev, "Skipping enable of already enabled panel\n");
		return;
	}

When next_bridge is a non-panel drm_bridge, there is no enabled-state guard
in the DRM bridge core, so next_bridge->funcs->atomic_enable() runs twice
without a matching second disable.

Additionally, if next_bridge sets pre_enable_prev_first,
drm_atomic_bridge_chain_pre_enable() runs ssd2825_bridge_atomic_pre_enable()
before next_bridge->funcs->atomic_pre_enable(), which would cause
next_bridge->funcs->atomic_enable() to run before next_bridge has been
prepared in atomic_pre_enable().

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261025133636.253505-1-clamor95@gmail.com?part=1