Re: [PATCH v3 17/24] driver core: Export get_dev_from_fwnode()

[Danilo Krummrich <dakr@kernel.org>]

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@google.com>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Tested-by: Hiago De Franco <hiago.franco@toradex.com> # Colibri iMX8X
> > Tested-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> # TI AM62A,Xilinx ZynqMP ZCU106
> > Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> > ---
> >  drivers/base/core.c    | 8 ++++++--
> >  include/linux/device.h | 1 +
> >  2 files changed, 7 insertions(+), 2 deletions(-)
> > 
> 
> Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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