linux-kernel - Re: [PATCH 0/4] media: Add devm-managed helper functions for media and V4L2 subsystems

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Message-ID: <20250723125520.GB6719@pendragon.ideasonboard.com>
Date: Wed, 23 Jul 2025 15:55:20 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Tarang Raval <tarang.raval@...iconsignals.io>
Cc: sakari.ailus@...ux.intel.com, hverkuil@...all.nl,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Ricardo Ribalda <ribalda@...omium.org>,
	Hans de Goede <hansg@...nel.org>,
	James Cowgill <james.cowgill@...ize.com>,
	Yunke Cao <yunkec@...gle.com>,
	Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
	Tommaso Merciai <tomm.merciai@...il.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/4] media: Add devm-managed helper functions for media
 and V4L2 subsystems

Hi Tarang,

On Wed, Jul 23, 2025 at 03:55:04PM +0530, Tarang Raval wrote:
> This patch series introduces devm-managed versions of several commonly used
> media and V4L2 initialization functions. These helpers simplify resource
> management by leveraging the devres infrastructure, ensuring automatic
> cleanup when the associated device is detached or the driver is unloaded.

I'll let Sakari review this, but overall, I don't think we want to take
this direction. Objects need to be refcounted instead of freed at remove
time. This patch series doesn't necessarily cause a regression as such,
but it will make it more difficult to fix life time management issues in
V4L2.

> Tested with IMX219 and OV2735 camera sensors on an i.MX8MP-based platform.
> 
> Tarang Raval (4):
>   media: mc: Add devm_media_entity_pads_init() helper
>   media: v4l: async: Add devm_v4l2_async_register_subdev_sensor() helper
>   media: v4l2: subdev: Add devm_v4l2_subdev_init_finalize() helper
>   media: v4l2-ctrls: Add devm_v4l2_ctrl_handler_init() helper
> 
>  drivers/media/mc/mc-entity.c              | 19 +++++++++++++++++++
>  drivers/media/v4l2-core/v4l2-async.c      | 19 +++++++++++++++++++
>  drivers/media/v4l2-core/v4l2-ctrls-core.c | 20 ++++++++++++++++++++
>  drivers/media/v4l2-core/v4l2-subdev.c     | 18 ++++++++++++++++++
>  include/media/media-entity.h              | 20 ++++++++++++++++++++
>  include/media/v4l2-async.h                | 18 ++++++++++++++++++
>  include/media/v4l2-ctrls.h                | 19 +++++++++++++++++++
>  include/media/v4l2-subdev.h               | 17 +++++++++++++++++
>  8 files changed, 150 insertions(+)
> 

-- 
Regards,

Laurent Pinchart