linux-kernel - Re: [PATCH v7 1/2] drm/bridge: move bridges_show logic from drm

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Message-ID: <20250225183621.6b33684b@booty>
Date: Tue, 25 Feb 2025 18:36:21 +0100
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Jani Nikula <jani.nikula@...ux.intel.com>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, Neil Armstrong
 <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, Laurent
 Pinchart <Laurent.pinchart@...asonboard.com>, 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>, Dmitry Baryshkov
 <dmitry.baryshkov@...aro.org>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 1/2] drm/bridge: move bridges_show logic from
 drm_debugfs.c

Hello Jani,

On Tue, 25 Feb 2025 18:36:41 +0200
Jani Nikula <jani.nikula@...ux.intel.com> wrote:

> On Tue, 25 Feb 2025, Luca Ceresoli <luca.ceresoli@...tlin.com> wrote:
> > In preparation to expose more info about bridges in debugfs, which will
> > require more insight into drm_bridge data structures, move the bridges_show
> > code to drm_bridge.c.
> >
> > Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> > Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>  
> 
> I hate myself for doing this on a patch that's at v7... but here goes.

Please don't! :-) This patch is new in v7, and a different (and
definitely worse) approach was present in v6, but there was nothing
before.

> Perhaps consider moving the bridges debugfs creation and fops to
> drm_bridge.c instead of just adding
> drm_bridge_debugfs_show_encoder_bridges().
> 
> For example, add drm_bridge_debugfs_add(struct drm_encoder *encoder),
> which then contains the debugfs_create_file() call.

I think it should go in drm_encoder.c, not drm_bridge.c, right? Here we
are showing the bridges attached to an encoder, so the entry point is
each encoder.

On the other hand in patch 2 we should move the
drm_debugfs_global_add() code to drm_bridge.c, as it's showing bridges
ina encoder-independent way.

And finally drm_bridge should export the common
drm_bridge_debugfs_show_bridge() function to drm_encoder.c.

Do you think this is correct?

> Interestingly, this lets you drop a lot of #ifdef CONFIG_DEBUG_FS. The
> compiler optimizes the fops struct and the functions away when
> debugfs_create_file() becomes a stub for CONFIG_DEBUG_FS=n. It becomes
> all around cleaner.

This surely makes the idea interesting. Cleaner code is always welcome.

Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com