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

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Message-ID: <777ee1b1-e5ce-ea29-8a48-f792354a22d1@codeaurora.org>
Date:   Fri, 16 Jun 2017 11:13:01 +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 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.

Thanks,
Archit

> Signed-off-by: Eric Anholt <eric@...olt.net>
> ---
>   drivers/gpu/drm/bridge/panel.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/bridge/panel.c b/drivers/gpu/drm/bridge/panel.c
> index 67fe19e5a9c6..8ed8a70799c7 100644
> --- a/drivers/gpu/drm/bridge/panel.c
> +++ b/drivers/gpu/drm/bridge/panel.c
> @@ -82,11 +82,14 @@ static int panel_bridge_attach(struct drm_bridge *bridge)
>   
>   	drm_mode_connector_attach_encoder(&panel_bridge->connector,
>   					  bridge->encoder);
> +	drm_atomic_helper_connector_reset(&panel_bridge->connector);
>   
>   	ret = drm_panel_attach(panel_bridge->panel, &panel_bridge->connector);
>   	if (ret < 0)
>   		return ret;
>   
> +	drm_connector_register(&panel_bridge->connector);
> +
>   	return 0;
>   }
>   
> 

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