linux-kernel - Re: [PATCH 1/7] drm/bridge: Support hotplugging panel-bridge.

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Message-ID: <8e148170-b626-b426-3c94-b93d2746f4ce@codeaurora.org>
Date:   Tue, 20 Jun 2017 09:18:00 +0530
From:   Archit Taneja <architt@...eaurora.org>
To:     Eric Anholt <eric@...olt.net>, dri-devel@...ts.freedesktop.org,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, devicetree@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] drm/bridge: Support hotplugging panel-bridge.



On 06/16/2017 08:13 PM, Eric Anholt wrote:
> Archit Taneja <architt@...eaurora.org> writes:
> 
>> On 06/16/2017 02:11 AM, Eric Anholt wrote:
>>> If the panel-bridge is being set up after the drm_mode_config_reset(),
>>> then the connector's state would never get initialized, and we'd
>>> dereference the NULL in the hotplug path.  We also need to register
>>> the connector, so that userspace can get at it.
>>>
>>
>> Shouldn't the KMS driver make sure the panel-bridge is set up before
>> drm_mode_config_reset? Is it the case when we're inserting the
>> panel-bridge driver as a module?
>>
>>
>> All the connectors that have been added are registered automatically
>> when drm_dev_register() is called by the KMS driver. Registering a
>> connector in the middle of setting up our driver is prone to race
>> conditions if the userspace decides to use them immediately.
> 
> Yeah, this is fixing initializing panel_bridge at DSI host_attach time,
> which in the case of a panel module that creates the DSI device
> (adv7533-style, like you said I should use as a reference) will be after
> drm_mode_config_reset() and drm_dev_register().

Okay. In the case of the msm kms driver, we defer probe until the
adv7533 module is inserted, only then we proceed to drm_mode_config_reset()
and drm_dev_register(). I assumed this was the general practice followed by
most kms drivers. I.,e the kms driver defers probe until all connector
related modules are inserted, and only then proceed to create a drm device.

Feedback from others on this would be appreciated, though.

Thanks,
Archit

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