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: <38f9e21c-ac64-45cd-a425-4036ad2ef32b@collabora.com>
Date: Tue, 13 Jan 2026 17:10:06 +0200
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Maxime Ripard <mripard@...nel.org>
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

Hi Maxime,

On 1/13/26 5:00 PM, Maxime Ripard wrote:
> 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?

Ups, I missed it somehow..

Thanks,
Cristian