linux-kernel - Re: [PATCH v2] drm/mipi-dsi: Add OF notifier handler

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Message-ID: <CAGXv+5FZtRb2R_OSwQQAUESM4p-UszXGWaDf8GW7+cHcZ7CuNQ@mail.gmail.com>
Date: Thu, 4 Jul 2024 15:04:33 +0800
From: Chen-Yu Tsai <wenst@...omium.org>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>
Cc: 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>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v2] drm/mipi-dsi: Add OF notifier handler

On Fri, Jun 28, 2024 at 6:31 PM Luca Ceresoli <luca.ceresoli@...tlin.com> wrote:
>
> Hello Chen-Yu,
>
> +Rob
>
> On Thu, 27 Jun 2024 15:19:03 +0800
> Chen-Yu Tsai <wenst@...omium.org> wrote:
>
> > Add OF notifier handler needed for creating/destroying MIPI DSI devices
> > according to dynamic runtime changes in the DT live tree. This code is
> > enabled when CONFIG_OF_DYNAMIC is selected.
> >
> > This is based on existing code for I2C and SPI subsystems.
> >
> > Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>
>
> Thanks for copying me on this patch. Could be useful for my
> hotplug-bridge work, however I'm aiming at writing code that works also
> for non-DSI so we'll see. The code looks pretty fine however.
>
> My concern however is about the usage of an OF reconfig notifier. A few
> days ago Rob Herring wrote:
>
> > a notifier is never a great design so
> > maybe we can come up with something better
>
> (https://lore.kernel.org/all/CAL_Jsq+=mGEJXsjq1UZFMJtHko_z+doiFMXnx9K7exDuznymSA@mail.gmail.com)
>
> So maybe this is something you can clarify with him.

Well, as mentioned in the commit message, this is based on existing code
found in the I2C and SPI cores. In these cases it is dealing with the
status flipping from disabled to okay, which then triggers the subsystem
to register a new device for the toggled device node.

If a better mechanism can be developed, then the existing code along with
the code I introduce here can be migrated over.

ChenYu

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