linux-kernel - Re: [PATCH v2] drm/bridge: Fix assignment of the of

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Message-ID: <20241101092049.GJ2473@pendragon.ideasonboard.com>
Date: Fri, 1 Nov 2024 11:20:49 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Sui Jingfeng <sui.jingfeng@...ux.dev>
Cc: Johan Hovold <johan@...nel.org>, neil.armstrong@...aro.org,
	Andrzej Hajda <andrzej.hajda@...el.com>,
	Robert Foss <rfoss@...nel.org>, Jonas Karlman <jonas@...boo.se>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Abel Vesa <abel.vesa@...aro.org>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH v2] drm/bridge: Fix assignment of the of_node of the
 parent to aux bridge

On Fri, Nov 01, 2024 at 11:49:07AM +0800, Sui Jingfeng wrote:
> 
> On 2024/11/1 00:23, Johan Hovold wrote:
> > On Thu, Oct 31, 2024 at 11:06:38PM +0800, Sui Jingfeng wrote:
> >
> >> But I think Johan do need more times to understand what exactly
> >> the real problem is. We do need times to investigate new method.
> > No, I know perfectly well what the (immediate) problem is here (I was
> > the one adding support for the of_node_reused flag some years back).
> >
> > I just wanted to make sure that the commit message was correct and
> > complete before merging (and also to figure out whether this particular
> > patch needed to be backported).
> 
> Well under such a design, having the child device sharing the 'OF' device
> node with it parent device means that one parent device can *only*
> create one AUX bridge child device.
> 
> Since If you create two or more child AUX bridge, *all* of them will
> call devm_drm_of_get_bridge(&auxdev->dev, auxdev->dev.of_node, 0, 0),
> then we will *contend* the same next bridge resource.
> 
> Because of the 'auxdev->dev.of_node' is same for all its instance.
> While other display bridges seems don't has such limitations.

Brainstorming a bit, I wonder if we could create a swnode for the
auxiliary device, instead of reusing the parent's OF node. This would
require switching the DRM OF-based APIs to fwnode, but that's easy and
mostly a mechanical change.

-- 
Regards,

Laurent Pinchart