linux-kernel - Re: [PATCH] platform: set of_node in platform_device_register

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Date:   Wed, 20 Feb 2019 11:51:01 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Måns Rullgård <mans@...sr.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] platform: set of_node in platform_device_register_full()

On Wed, Feb 20, 2019 at 11:41 AM Måns Rullgård <mans@...sr.com> wrote:
>
> "Rafael J. Wysocki" <rafael@...nel.org> writes:
>
> > On Mon, Feb 18, 2019 at 12:10 PM Måns Rullgård <mans@...sr.com> wrote:
> >>
> >> "Rafael J. Wysocki" <rafael@...nel.org> writes:
> >>
> >> > On Sat, Feb 16, 2019 at 5:50 PM Mans Rullgard <mans@...sr.com> wrote:
> >> >>
> >> >> If the provided fwnode is an OF node, set dev.of_node as well.
> >> >>
> >> >> Signed-off-by: Mans Rullgard <mans@...sr.com>
> >> >> ---
> >> >>  drivers/base/platform.c | 1 +
> >> >>  1 file changed, 1 insertion(+)
> >> >>
> >> >> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> >> >> index dff82a3c2caa..853a1d0e5845 100644
> >> >> --- a/drivers/base/platform.c
> >> >> +++ b/drivers/base/platform.c
> >> >> @@ -512,6 +512,7 @@ struct platform_device *platform_device_register_full(
> >> >>
> >> >>         pdev->dev.parent = pdevinfo->parent;
> >> >>         pdev->dev.fwnode = pdevinfo->fwnode;
> >> >> +       pdev->dev.of_node = of_node_get(to_of_node(pdev->dev.fwnode));
> >> >
> >> > of_node_get() generally does a kobject_get() on the node's kobject, so
> >> > when is that reference dropped?  Or if it doesn't need to be dropped
> >> > at all, why is this the case?
> >>
> >> platform_device_release() calls of_device_node_put().
> >
> > Yes, it does, but this is the reference that's already acquired for
> > devices added while parsing DT, isn't it?
> >
> > Your change adds an extra reference AFAICS.
> >
> > Also, why is this patch needed?
>
> Some drivers are just shims that create extra "glue" devices with the DT
> device as parent and have the real driver bind to these.  In other
> cases, the same real driver matches the DT node directly.  When a glue
> device is used, it needs to get a reference to the original DT node in
> order for the main driver to access properties and child nodes.
>
> Right now, my problem is that the suxi-musb driver creates such a glue
> device for the musb core driver to bind to without setting of_node.
> This means devices attached to this USB interface don't get associated
> with DT nodes, if present, the way they do with EHCI.

You really should describe problems that you want to address in patch
changelogs.  This helps a lot to understand the motivation for the
changes.

> The sunxi-musb driver uses platform_device_register_full(), so this
> seemed like the easiest way to let it set of_node of the new device.
> Since this creates a second reference to the same node, of_node_get()
> is required.

But what about devices that already have of_node set at this point?

Maybe check if of_node is NULL before trying to set it?