On Wed, Jul 2, 2025 at 12:26 PM Danilo Krummrich [off-list ref] wrote:

On Wed, Jul 02, 2025 at 09:34:12AM +0200, Greg Kroah-Hartman wrote:

quoted

On Tue, Jul 01, 2025 at 01:47:19PM +0200, Ulf Hansson wrote:

quoted

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 <redacted>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Tested-by: Hiago De Franco <redacted> # Colibri iMX8X
Tested-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> # TI AM62A,Xilinx ZynqMP ZCU106
Signed-off-by: Ulf Hansson <redacted>
---
 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.

Not enough for what?

The caller also needs to ensure that the device the fwnode has a pointer to has
not been released yet.

Why? The point of the API is to give you the driver core's notion of
the primary device that corresponds to a fwnode at that instant.

There's no refcount needed for that. This is just a simpler way than
looping through all the devices to find the first device that has that
specific fwnode.

It's only the device that needs to be ref counted because the caller
needs to do stuff with it.

-Saravana