linux-kernel - Re: [PATCH 1/5] drm/bridge: Add drm_bridge_find_by

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Date: Tue, 23 Jan 2024 17:15:10 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Sui Jingfeng <sui.jingfeng@...ux.dev>
Cc: David Airlie <airlied@...il.com>,
	Neil Armstrong <neil.armstrong@...aro.org>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	Daniel Vetter <daniel@...ll.ch>, dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] drm/bridge: Add drm_bridge_find_by_fwnode() helper

Hi Sui,

On Tue, Jan 23, 2024 at 04:01:28PM +0800, Sui Jingfeng wrote:
> On 2024/1/23 09:17, Laurent Pinchart wrote:
> > On Tue, Jan 23, 2024 at 12:32:16AM +0800, Sui Jingfeng wrote:
> >> Because ACPI based systems only has the fwnode associated, the of_node
> >> member of struct device is NULL. To order to move things forward, we add
> >> drm_bridge_find_by_fwnode() to extend the support.
> >>
> >> Signed-off-by: Sui Jingfeng <sui.jingfeng@...ux.dev>
> >
> > Could we switch completely to fwnode, instead of maintaining the fwnode
> > and OF options side-by-side ?
> 
> The side-by-side approach allow us to migrate smoothly,

But it increases the maintenance burden for the duration of the
migration. I fear the migration would span years, with nobody really
taking active care of it, and the OF and non-OF API will have a risk to
diverge.

> the main consideration is that the OF approach has been
> works very well, it is flexible and very successful in
> the embedded world.

fwnode is a superset of OF, so I don't expect issues switching from OF
to fwnode. For the non-OF, non-fwnode users, that's possibly a different
question.

> It seems that the fwnode API could NOT replace the OF
> options completely. For example, the'of_device_id' and 'of_match_table' related things are always there, there

Yes, and that's not a problem. OF drivers still use of_device_id and
of_match_table, even if they use the fwnode API. No issue there.

> are large well-established helpers and subroutines and
> already formed as a standard. Some part of it may suffer
> from backward compatibility problems.

fwnode has been designed to offer the same API as OF for drivers. If
something is missing, it can be raised with the maintainers.

> So I want to leave some space to other programmers.
> Maybe there are other programmers who feel that using
> OF alone is enough for a specific problem(domain).

-- 
Regards,

Laurent Pinchart