linux-kernel - Re: [PATCH v3 17/24] driver core: Export get_dev_from

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Message-ID: <aGWH2mH6iZJ3s3lL@pollux>
Date: Wed, 2 Jul 2025 21:26:18 +0200
From: Danilo Krummrich <dakr@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Ulf Hansson <ulf.hansson@...aro.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Stephen Boyd <sboyd@...nel.org>, linux-pm@...r.kernel.org,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Michael Grzeschik <m.grzeschik@...gutronix.de>,
	Bjorn Andersson <andersson@...nel.org>,
	Abel Vesa <abel.vesa@...aro.org>, Peng Fan <peng.fan@....nxp.com>,
	Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
	Johan Hovold <johan@...nel.org>,
	Maulik Shah <maulik.shah@....qualcomm.com>,
	Michal Simek <michal.simek@....com>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Jonathan Hunter <jonathanh@...dia.com>,
	Hiago De Franco <hiago.franco@...adex.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 17/24] driver core: Export get_dev_from_fwnode()

On Wed, Jul 02, 2025 at 09:34:12AM +0200, Greg Kroah-Hartman wrote:
> On Tue, Jul 01, 2025 at 01:47:19PM +0200, Ulf Hansson wrote:
> > It has turned out get_dev_from_fwnode() is useful at a few other places
> > outside of the driver core, as in gpiolib.c for example. Therefore let's
> > make it available as a common helper function.
> > 
> > Suggested-by: Saravana Kannan <saravanak@...gle.com>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Tested-by: Hiago De Franco <hiago.franco@...adex.com> # Colibri iMX8X
> > Tested-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com> # TI AM62A,Xilinx ZynqMP ZCU106
> > Signed-off-by: Ulf Hansson <ulf.hansson@...aro.org>
> > ---
> >  drivers/base/core.c    | 8 ++++++--
> >  include/linux/device.h | 1 +
> >  2 files changed, 7 insertions(+), 2 deletions(-)
> > 
> 
> Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

I'm a bit concerned about exporting get_dev_from_fwnode() -- at least without a
clear note on that this helper should be used with caution.

AFAIK, a struct fwnode_handle instance does not have a reference count for its
struct device pointer.

Hence, calling get_dev_from_fwnode() with a valid fwnode handle is not enough.
The caller also needs to ensure that the device the fwnode has a pointer to has
not been released yet.

If this really needs to be exported, can we please add documentation covering
this properly?

- Danilo