linux-kernel - Re: [PATCH v1] driver core: fw_devlink: Don't create device links for devices not on a bus

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Message-ID: <CAGETcx8B-9GJr_wCRLqH=eBKY+f=Cd+LGWfM+GQGt6HzOj1TdQ@mail.gmail.com>
Date:   Wed, 1 Sep 2021 14:55:50 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        kernel-team@...roid.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] driver core: fw_devlink: Don't create device links for
 devices not on a bus

On Wed, Sep 1, 2021 at 12:14 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Tue, Aug 31, 2021 at 11:57:45PM -0700, Saravana Kannan wrote:
> > On Tue, Aug 31, 2021 at 11:24 PM Greg Kroah-Hartman
> > <gregkh@...uxfoundation.org> wrote:
> > >
> > > On Tue, Aug 31, 2021 at 03:45:10PM -0700, Saravana Kannan wrote:
> > > > Devices that are not on a bus will never have a driver bound to it. So,
> > > > fw_devlink should not create device links for it as it can cause probe
> > > > issues[1] or sync_state() call back issues[2].
> > > >
> > > > [1] - https://lore.kernel.org/lkml/CAGETcx_xJCqOWtwZ9Ee2+0sPGNLM5=F=djtbdYENkAYZa0ynqQ@mail.gmail.com/
> > > > [2] - https://lore.kernel.org/lkml/CAPDyKFo9Bxremkb1dDrr4OcXSpE0keVze94Cm=zrkOVxHHxBmQ@mail.gmail.com/
> > > > Fixes: f9aa460672c9 ("driver core: Refactor fw_devlink feature")
> > > > Reported-by: Ulf Hansson <ulf.hansson@...aro.org>
> > > > Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> > > > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> > > > ---
> > > >  drivers/base/core.c | 16 ++++++++++++++++
> > > >  1 file changed, 16 insertions(+)
> > > >
> > > > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > > > index f6360490a4a3..304a06314656 100644
> > > > --- a/drivers/base/core.c
> > > > +++ b/drivers/base/core.c
> > > > @@ -1719,8 +1719,24 @@ static int fw_devlink_create_devlink(struct device *con,
> > > >       struct device *sup_dev;
> > > >       int ret = 0;
> > > >
> > > > +     /*
> > > > +      * If a consumer device is not on a bus (i.e. a driver will never bind
> > > > +      * to it), it doesn't make sense for fw_devlink to create device links
> > > > +      * for it.
> > > > +      */
> > > > +     if (con->bus == NULL)
> > > > +             return -EINVAL;
> > > > +
> > >
> > > Why would a device not be on a bus that has to do with a driver needing
> > > it?  What types of devices are these?
> >
> > I'm not sure what you are asking, because it seems like a question
> > you'd know the answer to. What I'm trying to say is that
> > bus_probe_device() is obviously only possible if the device is on a
> > bus. And fw_devlink creates managed device links that track if a
> > device is bound to a driver. So it doesn't make sense to create the
> > device link if the device is not on a bus.
> >
> > There are plenty of examples for this -- like all the devices that get
> > added to a class? For example the platform bus or the mdio bus itself
> > are devices that are added to a class instead of a bus.
> >
> > Not sure if I answered your question. Let me know.
>
> Sorry, that was a vague question.
>
> I was trying to say, "how can a device that is not attached to a bus at
> all even be called for this?"

This code path is called for all device_add()s.

> Who would be making that type of
> connection, what subsystem is causing this to happen?

fw_devlink trying to interpret DT dependencies can sometimes end up in
this situation for some uncommon cases. But it's not helping [1] or
[2], so for now let's drop this patch. I'll come back to this if I
need this to fix any real issue.

-Saravana