linux-kernel - Re: [PATCH v2 3/4] drm/bridge: dw-hdmi-qp: Add high TMDS clock ratio and scrambling support

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Message-ID: <20260113-unselfish-russet-chicken-80d3c3@houat>
Date: Tue, 13 Jan 2026 16:00:01 +0100
From: Maxime Ripard <mripard@...nel.org>
To: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, 
	Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
	Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman <jonas@...boo.se>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Sandy Huang <hjc@...k-chips.com>, 
	Heiko Stübner <heiko@...ech.de>, Andy Yan <andy.yan@...k-chips.com>, kernel@...labora.com, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org, 
	Diederik de Haas <diederik@...ow-tech.com>, Maud Spierings <maud_spierings@...mail.com>
Subject: Re: [PATCH v2 3/4] drm/bridge: dw-hdmi-qp: Add high TMDS clock ratio
 and scrambling support

On Tue, Jan 13, 2026 at 12:26:20AM +0200, Cristian Ciocaltea wrote:
> @@ -902,13 +981,74 @@ static void dw_hdmi_qp_bridge_atomic_disable(struct drm_bridge *bridge,
>  
>  	hdmi->tmds_char_rate = 0;
>  
> +	dw_hdmi_qp_disable_scramb(hdmi);
> +
> +	hdmi->curr_conn = NULL;
>  	hdmi->phy.ops->disable(hdmi, hdmi->phy.data);
>  }
>  
> -static enum drm_connector_status
> -dw_hdmi_qp_bridge_detect(struct drm_bridge *bridge, struct drm_connector *connector)
> +static int dw_hdmi_qp_reset_link(struct dw_hdmi_qp *hdmi,
> +				 struct drm_connector *conn,
> +				 struct drm_modeset_acquire_ctx *ctx)
> +{
> +	struct drm_crtc *crtc;
> +	u8 config;
> +	int ret;
> +
> +	if (!conn->state)
> +		return 0;
> +
> +	crtc = conn->state->crtc;
> +	if (!crtc)
> +		return 0;
> +
> +retry:
> +	ret = drm_modeset_lock(&crtc->mutex, ctx);
> +	if (ret)
> +		goto check_err;
> +
> +	if (!crtc->state->active)
> +		return 0;
> +
> +	if (conn->state->commit &&
> +	    !try_wait_for_completion(&conn->state->commit->hw_done))
> +		return 0;
> +
> +	ret = drm_scdc_readb(hdmi->bridge.ddc, SCDC_TMDS_CONFIG, &config);
> +	if (ret < 0) {
> +		dev_err(hdmi->dev, "Failed to read TMDS config: %d\n", ret);
> +		return 0;
> +	}
> +
> +	if (!!(config & SCDC_SCRAMBLING_ENABLE) == hdmi->scramb_enabled)
> +		return 0;
> +
> +	dev_dbg(hdmi->dev, "%s resetting crtc\n", __func__);
> +
> +	drm_atomic_helper_connector_hdmi_hotplug(conn, connector_status_connected);
> +
> +	/*
> +	 * Conform to HDMI 2.0 spec by ensuring scrambled data is not sent
> +	 * before configuring the sink scrambling, as well as suspending any
> +	 * TMDS transmission while changing the TMDS clock rate in the sink.
> +	 */
> +	ret = drm_atomic_helper_reset_crtc(crtc, ctx);
> +
> +check_err:
> +	if (ret == -EDEADLK) {
> +		drm_modeset_backoff(ctx);
> +		goto retry;
> +	}
> +
> +	return ret;
> +}
> +
> +static int dw_hdmi_qp_bridge_detect(struct drm_bridge *bridge,
> +				    struct drm_connector *connector,
> +				    struct drm_modeset_acquire_ctx *ctx)
>  {
>  	struct dw_hdmi_qp *hdmi = bridge->driver_private;
> +	enum drm_connector_status status;
>  	const struct drm_edid *drm_edid;
>  
>  	if (hdmi->no_hpd) {
> @@ -919,7 +1059,15 @@ dw_hdmi_qp_bridge_detect(struct drm_bridge *bridge, struct drm_connector *connec
>  			return connector_status_disconnected;
>  	}
>  
> -	return hdmi->phy.ops->read_hpd(hdmi, hdmi->phy.data);
> +	status = hdmi->phy.ops->read_hpd(hdmi, hdmi->phy.data);
> +
> +	dev_dbg(hdmi->dev, "%s status=%d scramb=%d\n", __func__,
> +		status, hdmi->scramb_enabled);
> +
> +	if (status == connector_status_connected && hdmi->scramb_enabled)
> +		dw_hdmi_qp_reset_link(hdmi, connector, ctx);
> +
> +	return status;
>  }

We have drm_bridge_helper_reset_crtc() now, any reason you didn't use it?

Maxime

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