linux-kernel - Re: [PATCH RFC] driver core: Ensure DT devices always have fwnode set

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Date:   Mon, 9 Nov 2020 11:25:39 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Mark Brown <broonie@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Daniel Mentz <danielmentz@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Frank Rowand <frowand.list@...il.com>
Subject: Re: [PATCH RFC] driver core: Ensure DT devices always have fwnode set

On Fri, Nov 6, 2020 at 1:09 PM Saravana Kannan <saravanak@...gle.com> wrote:
>
> +Rob and Frank
>
> On Fri, Nov 6, 2020 at 7:09 AM Mark Brown <broonie@...nel.org> wrote:
> >
> > Currently the fwnode API and things that rely on it like fw_devlink will
> > not reliably work for devices created from DT since each subsystem that
> > creates devices must individually set dev->fwnode in addition to setting
> > dev->of_node, currently a number of subsystems don't do so. Ensure that
> > this can't get missed by setting fwnode from of_node if it's not
> > previously been set by the subsystem.
> >
> > Reported-by: Saravana Kannan <saravanak@...gle.com>
> > Signed-off-by: Mark Brown <broonie@...nel.org>
> > ---
> >
> > *Very* minimally tested.
> >
> >  drivers/base/core.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index d661ada1518f..658626bafd76 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -2864,6 +2864,10 @@ int device_add(struct device *dev)
> >         if (parent && (dev_to_node(dev) == NUMA_NO_NODE))
> >                 set_dev_node(dev, dev_to_node(parent));
> >
> > +       /* ensure that fwnode is set up */
> > +       if (IS_ENABLED(CONFIG_OF) && dev->of_node && !dev->fwnode)
> > +               dev->fwnode = of_fwnode_handle(dev->of_node);
> > +
>
> I don't think we should add more CONFIG_OF specific code in drivers/base/

It's fwnode specific code because it's fwnode that needs it...

> If you want to do this in "one common place", then I think the way to
> do this is have include/linux/of.h provide something like:
> void of_set_device_of_node(dev, of_node)
> {
>     dev->of_node = of_node;
>     dev->fw_node = &of_node->fwnode;
>    /* bunch of other housekeeping like setting OF_POPULATED and doing
> proper of_node_get() */
>    // Passing NULL for of_node could undo all the above for dev->of_node.
> }
>
> And all the subsystems that create their own device from an of_node
> should use of_set_device_of_node() to set the device's of_node. That
> way, all this is done in a consistent manner across subsystems and
> avoid all of the of_get/put() and OF_POPULATED set/clear strewn all
> over the subsystems.

Perhaps a fwnode call in device_add instead that implements the above
and anything else needed for each type of fwnode. It might even be
possible with that to get rid of most of
of_platform_device_create_pdata() and of_device_add(). IIRC, those
were pretty much copies of the core code.

That would also be less fragile than having a coccinelle script.

Rob