linux-kernel - Re: [PATCH] drm/mipi-dsi: Fix devm unregister & detach

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Date: Wed, 26 Jun 2024 10:49:47 +0200
From: Maxime Ripard <mripard@...nel.org>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, 
	Daniel Vetter <daniel@...ll.ch>, Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>
Subject: Re: [PATCH] drm/mipi-dsi: Fix devm unregister & detach

Hi,

On Wed, Jun 19, 2024 at 12:07:48PM GMT, Tomi Valkeinen wrote:
> From: Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>
> 
> When a bridge driver uses devm_mipi_dsi_device_register_full() or
> devm_mipi_dsi_attach(), the resource management is moved to devres,
> which releases the resource automatically when the bridge driver is
> unbound.
> 
> However, if the DSI host goes away first, the host unregistration code
> will automatically detach and unregister any DSI peripherals, without
> notifying the devres about it. So when the bridge driver later is
> unbound, the resources are released a second time, leading to crash.

That's super surprising. mipi_dsi_device_unregister calls
device_unregister, which calls device_del, which in turn calls
devres_release_all.

If that doesn't work like that, then it's what needs to be fixed, and
not worked around in the MIPI-DSI bus.

Maxime

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