linux-kernel - Re: [PATCH v9 0/6] MHDP8546 fixes related to DBANC usecase

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Message-ID: <85b86f9f-2ab9-4bfd-b06b-9543244507a7@ti.com>
Date: Thu, 20 Nov 2025 13:18:43 +0530
From: Harikrishna shenoy <h-shenoy@...com>
To: Maxime Ripard <mripard@...nel.org>, Tomi Valkeinen
	<tomi.valkeinen@...asonboard.com>
CC: <Laurent.pinchart@...asonboard.com>, <airlied@...il.com>,
	<andrzej.hajda@...el.com>, <andy.yan@...k-chips.com>,
	<aradhya.bhatia@...ux.dev>, <devarsht@...com>, <dianders@...omium.org>,
	<dri-devel@...ts.freedesktop.org>, <javierm@...hat.com>,
	<jernej.skrabec@...il.com>, <jonas@...boo.se>,
	<linux-kernel@...r.kernel.org>, <linux@...blig.org>,
	<luca.ceresoli@...tlin.com>, <lumag@...nel.org>, <lyude@...hat.com>,
	<maarten.lankhorst@...ux.intel.com>, <mordan@...ras.ru>,
	<neil.armstrong@...aro.org>, <rfoss@...nel.org>, <s-jain1@...com>,
	<simona@...ll.ch>, <tzimmermann@...e.de>, <u-kumar1@...com>
Subject: Re: [PATCH v9 0/6] MHDP8546 fixes related to DBANC usecase



On 18/11/25 21:50, Maxime Ripard wrote:
> On Tue, Nov 18, 2025 at 04:52:49PM +0200, Tomi Valkeinen wrote:
>> Hi,
>>
>> On 18/11/2025 14:40, Maxime Ripard wrote:
>>> Hi,
>>>
>>> On Tue, Nov 18, 2025 at 05:22:49PM +0530, Harikrishna Shenoy wrote:
>>>> With the DBANC framework, the connector is no longer initialized in
>>>> bridge_attach() when the display controller sets the
>>>> DRM_BRIDGE_ATTACH_NO_CONNECTOR flag.
>>>> This causes a null pointer dereference in cdns_mhdp_modeset_retry_fn()
>>>> when trying to access &conn->dev->mode_config.mutex.
>>>> Observed on a board where EDID read failed.
>>>> (log: https://gist.github.com/Jayesh2000/233f87f9becdf1e66f1da6fd53f77429)
>>>>
>>>> Patch 1 adds a connector_ptr which takes care of both
>>>> DBANC and !DBANC case by setting the pointer in appropriate hooks
>>>> and checking for pointer validity before accessing the connector.
>>>> Patch 2 adds mode validation hook to bridge fucntions.
>>>> Patch 3 fixes HDCP to work with both DBANC and !DBANC case by
>>>> moving HDCP state handling into the bridge atomic check in line with
>>>> the DBANC model.
>>>> Patches 4,5 do necessary cleanup and alignment for using
>>>> connector pointer.
>>>
>>> It's mentioned several times in your series, and it might be obvious to
>>> you, but documenting what is the "DBANC framework" is would be helpful.
>>> I have no idea what it's about, and it appears that Google doesn't know
>>> either.
>> Yes, I was a bit baffled initially. DRM_BRIDGE_ATTACH_NO_CONNECTOR.
> 
> Oooooh, thanks
> 
>> I think it makes sense to only use "DBANC" if it's first introduced in
>> that patch. So don't have a patch that just uses "DBANC", even if the
>> previous patch did explain what it means. And if there's just one or two
>> "DBANC"s, just spell it out "DRM_BRIDGE_ATTACH_NO_CONNECTOR".
> 
> Yeah, I'd go even further. Acronyms are fun but something being obvious
> is better still. Use the proper flag name every time.
> 
> Maxime

Hi Maxime,

Thanks for pointing this out, will resend the series replacing the 
acronym with proper flag name.

Regards.