linux-kernel - Re: [PATCH v2 2/5] drm/panel: panel-simple: make panel_dpi_probe return a panel

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Message-ID: <878qldd04p.fsf@minerva.mail-host-address-is-not-set>
Date: Fri, 27 Jun 2025 11:06:30 +0200
From: Javier Martinez Canillas <javierm@...hat.com>
To: Maxime Ripard <mripard@...nel.org>, Neil Armstrong
 <neil.armstrong@...aro.org>, Jessica Zhang <quic_jesszhan@...cinc.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann
 <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter
 <simona@...ll.ch>, Luca Ceresoli <luca.ceresoli@...tlin.com>, Anusha
 Srivatsa <asrivats@...hat.com>, Francesco Dolcini <francesco@...cini.it>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, Maxime
 Ripard <mripard@...nel.org>
Subject: Re: [PATCH v2 2/5] drm/panel: panel-simple: make panel_dpi_probe
 return a panel_desc

Maxime Ripard <mripard@...nel.org> writes:

> If the panel-simple driver is probed from a panel-dpi compatible, the
> driver will use an empty panel_desc structure as a descriminant. It
> will then allocate and fill another panel_desc as part of its probe.
>
> However, that allocation needs to happen after the panel_simple
> structure has been allocated, since panel_dpi_probe(), the function
> doing the panel_desc allocation and initialization, takes a panel_simple
> pointer as an argument.
>
> This pointer is used to fill the panel_simple->desc pointer that is
> still initialized with the empty panel_desc when panel_dpi_probe() is
> called.
>
> Since commit de04bb0089a9 ("drm/panel/panel-simple: Use the new
> allocation in place of devm_kzalloc()"), we will need the panel
> connector type found in panel_desc to allocate panel_simple. This
> creates a circular dependency where we need panel_desc to create
> panel_simple, and need panel_simple to create panel_desc.
>
> Let's break that dependency by making panel_dpi_probe simply return the
> panel_desc it initialized and move the panel_simple->desc assignment to
> the caller.
>
> This will not fix the breaking commit entirely, but will move us towards
> the right direction.
>
> Fixes: de04bb0089a9 ("drm/panel/panel-simple: Use the new allocation in place of devm_kzalloc()")
> Signed-off-by: Maxime Ripard <mripard@...nel.org>
> ---

Reviewed-by: Javier Martinez Canillas <javierm@...hat.com>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat