linux-kernel - Re: [PATCH v7 3/6] drm/bridge: cadence: cdns-mhdp8546-core: Set the mhdp connector earlier in atomic

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Message-ID: <gtj43rfr2dgegutffma34w5bhvdmvx44jhwxgxb3ficqh5tm53@2iyr6ho3qfdh>
Date: Mon, 6 Oct 2025 02:12:19 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Harikrishna Shenoy <h-shenoy@...com>
Cc: andrzej.hajda@...el.com, neil.armstrong@...aro.org, rfoss@...nel.org,
        Laurent.pinchart@...asonboard.com, jonas@...boo.se,
        jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com,
        mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com,
        simona@...ll.ch, lumag@...nel.org, dianders@...omium.org,
        andy.yan@...k-chips.com, mordan@...ras.ru, linux@...blig.org,
        viro@...iv.linux.org.uk, aradhya.bhatia@...ux.dev, javierm@...hat.com,
        tomi.valkeinen@...asonboard.com, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, devarsht@...com, u-kumar1@...com,
        s-jain1@...com, lyude@...hat.com, luca.ceresoli@...tlin.com
Subject: Re: [PATCH v7 3/6] drm/bridge: cadence: cdns-mhdp8546-core: Set the
 mhdp connector earlier in atomic_enable()

On Mon, Sep 29, 2025 at 02:09:33PM +0530, 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(). Now that we have the connector
> pointer in mhdp bridge structure, so set the mhdp->connector in
> atomic_enable() earlier to avoid possible NULL pointer dereference
> in recovery paths like modeset_retry_fn() with the DBANC flag set.
> 
> Fixes: c932ced6b585 ("drm/tidss: Update encoder/bridge chain connect model")

This Fixes tag means that this patch can be attempted to be backported
back to v6.5 (even w/o cc:stable, etc). I know that it is a pain, but
please move all Fixes to the top of the series. Yes, you want to drop
non-DBANC case first and then fix everything. It doesn't look like it is
a correct approach for the sake of maintaing the -stable branches.

> Signed-off-by: Jayesh Choudhary <j-choudhary@...com>
> Signed-off-by: Harikrishna Shenoy <h-shenoy@...com>
> ---
>  .../drm/bridge/cadence/cdns-mhdp8546-core.c   | 20 +++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 

-- 
With best wishes
Dmitry