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

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Message-ID: <20170623090446.ogaoqg7gcsiaxs4a@phenom.ffwll.local>
Date:   Fri, 23 Jun 2017 11:04:47 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Eric Anholt <eric@...olt.net>
Cc:     dri-devel@...ts.freedesktop.org,
        Archit Taneja <architt@...eaurora.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, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] drm/bridge: Support hotplugging panel-bridge.

On Thu, Jun 15, 2017 at 01:41:24PM -0700, 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.
> 
> Signed-off-by: Eric Anholt <eric@...olt.net>

I've not read all the details of the discussion here, just a comment on
what this implies if we go with this.

> ---
>  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);

I'm not sure we want to tie the ->reset stuff in with other helpers. One
of the design goals I had with all things atomic was to make helpers much
more modular, and imo the reset is one such piece - a driver might want to
instead reconstruct state from hw using something like i915's hw state
readout/compare/verify framework.

If we can solve this init ordering issue without adding a depency on the
reset stuff that would be a bit neater imo. But that's just my 2 cents.

Cheers, Daniel

>  
>  	ret = drm_panel_attach(panel_bridge->panel, &panel_bridge->connector);
>  	if (ret < 0)
>  		return ret;
>  
> +	drm_connector_register(&panel_bridge->connector);
> +
>  	return 0;
>  }
>  
> -- 
> 2.11.0
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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