linux-kernel - Re: [PATCH v2 0/5] Add support for GE SUNH hot-pluggable connector (was: "drm: add support for hot-pluggable bridges")

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Message-ID: <20240514191117.519b274c@booty>
Date: Tue, 14 May 2024 19:11:17 +0200
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Rob Herring <robh@...nel.org>
Cc: Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, 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>, Daniel Vetter <daniel@...ll.ch>, Derek Kiernan
 <derek.kiernan@....com>, Dragan Cvetic <dragan.cvetic@....com>, Arnd
 Bergmann <arnd@...db.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Saravana Kannan <saravanak@...gle.com>, Paul Kocialkowski
 <contact@...lk.fr>, Hervé Codina
 <herve.codina@...tlin.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, Paul
 Kocialkowski <paul.kocialkowski@...tlin.com>
Subject: Re: [PATCH v2 0/5] Add support for GE SUNH hot-pluggable connector
 (was: "drm: add support for hot-pluggable bridges")

Hello Rob,

On Fri, 10 May 2024 11:44:49 -0500
Rob Herring <robh@...nel.org> wrote:

> On Fri, May 10, 2024 at 09:10:36AM +0200, Luca Ceresoli wrote:

[...]

> > Overall approach
> > ================
> > 
> > Device tree overlays appear as the most natural solution to support the
> > addition and removal of devices from a running system.
> > 
> > Several features are missing from the mainline Linux kernel in order to
> > support this use case:
> > 
> >  1. runtime (un)loading of device tree overlays is not supported  
> 
> Not true. Device specific applying of overlays has been supported 
> since we merged DT overlay support. What's not supported is a general 
> purpose interface to userspace to change any part of the DT at any point 
> in time.

I think I should replace "supported" with "exposed [to user space]". In
other words, there is no user of of_overlay_fdt_apply() /
of_overlay_remove*() in mainline Linux, except in unittest. Would it be
a correct rewording?

> >  2. if enabled, overlay (un)loading exposes several bugs  
> 
> Hence why there is no general purpose interface.

Absolutely.

Best regards,
Luca

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