linux-kernel - Re: [PATCH v5 3/6] drm/bridge: cadence: cdns-mhdp8546-core: Set the mhdp connector earlier in atomic

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Message-ID: <6fa1a8d5-149e-437d-aef0-587c49957197@ideasonboard.com>
Date: Mon, 1 Sep 2025 13:05:02 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Harikrishna Shenoy <h-shenoy@...com>
Cc: jonas@...boo.se, jernej.skrabec@...il.com,
 maarten.lankhorst@...ux.intel.com, tzimmermann@...e.de, airlied@...il.com,
 simona@...ll.ch, lyude@...hat.com, luca.ceresoli@...tlin.com,
 viro@...iv.linux.org.uk, andy.yan@...k-chips.com, linux@...blig.org,
 javierm@...hat.com, linux-kernel@...r.kernel.org, devarsht@...com,
 j-choudhary@...com, u-kumar1@...com, s-jain1@...com,
 andrzej.hajda@...el.com, neil.armstrong@...aro.org, rfoss@...nel.org,
 Laurent.pinchart@...asonboard.com, mripard@...nel.org, lumag@...nel.org,
 dianders@...omium.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v5 3/6] drm/bridge: cadence: cdns-mhdp8546-core: Set the
 mhdp connector earlier in atomic_enable()

Hi,

On 11/08/2025 10:59, Harikrishna Shenoy wrote:
> From: Jayesh Choudhary <j-choudhary@...com>
> 
> In case if we get errors in cdns_mhdp_link_up() or cdns_mhdp_reg_read()
> in atomic_enable, we will go to cdns_mhdp_modeset_retry_fn() and will hit
> NULL pointer while trying to access the mutex. We need the connector to
> be set before that. Unlike in legacy !(DBANC) cases, we do not have
> connector initialised in bridge_attach(). So set the mhdp->connector
> in atomic_enable() earlier to avoid possible NULL pointer.
> 
> Fixes: c932ced6b585 ("drm/tidss: Update encoder/bridge chain connect model")
> Signed-off-by: Jayesh Choudhary <j-choudhary@...com>
> ---
>  .../drm/bridge/cadence/cdns-mhdp8546-core.c   | 20 +++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> index c2ce3d6e5a88..b2f5a48cac2d 100644
> --- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> +++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
> @@ -1759,12 +1759,21 @@ static void cdns_mhdp_atomic_enable(struct drm_bridge *bridge,
>  	struct drm_bridge_state *new_state;
>  	const struct drm_display_mode *mode;
>  	u32 resp;
> -	int ret;
> +	int ret = 0;
>  
>  	dev_dbg(mhdp->dev, "bridge enable\n");
>  
>  	mutex_lock(&mhdp->link_mutex);
>  
> +	mhdp->connector = drm_atomic_get_new_connector_for_encoder(state,
> +								   bridge->encoder);
> +	if (WARN_ON(!mhdp->connector))
> +		goto out;
> +
> +	conn_state = drm_atomic_get_new_connector_state(state, mhdp->connector);
> +	if (WARN_ON(!conn_state))
> +		goto out;

You are just moving code here, but... Shouldn't these be errors? If I
read this right, ret is 0 here, and thus if we hit either of those
issues above, we'll return 0.

 Tomi

> +
>  	if (mhdp->plugged && !mhdp->link_up) {
>  		ret = cdns_mhdp_link_up(mhdp);
>  		if (ret < 0)
> @@ -1784,15 +1793,6 @@ static void cdns_mhdp_atomic_enable(struct drm_bridge *bridge,
>  	cdns_mhdp_reg_write(mhdp, CDNS_DPTX_CAR,
>  			    resp | CDNS_VIF_CLK_EN | CDNS_VIF_CLK_RSTN);
>  
> -	mhdp->connector = drm_atomic_get_new_connector_for_encoder(state,
> -								   bridge->encoder);
> -	if (WARN_ON(!mhdp->connector))
> -		goto out;
> -
> -	conn_state = drm_atomic_get_new_connector_state(state, mhdp->connector);
> -	if (WARN_ON(!conn_state))
> -		goto out;
> -
>  	if (mhdp->hdcp_supported &&
>  	    mhdp->hw_state == MHDP_HW_READY &&
>  	    conn_state->content_protection ==