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

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Message-ID: <CAJZ5v0hvfVgTigfycGmV7u-Rj6i2fyzhrJjdiWEQfq4PxgFzwA@mail.gmail.com>
Date:   Wed, 20 Feb 2019 12:08:49 +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 12:02 PM Måns Rullgård <mans@...sr.com> wrote:
>
> "Rafael J. Wysocki" <rafael@...nel.org> writes:
>
> > 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.
>
> Do you want me to send a new patch with the above explanation in the
> commit message?

Yes, please.

> >> 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?
>
> It's a brand new device allocated a few lines above.  of_node has to be
> null here.

Right, sorry for the confusion.