linux-kernel - Re: [PATCH v1 3/5] driver core: Allow fwnode_operations.add

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Date:   Tue, 5 Nov 2019 14:52:21 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Len Brown <lenb@...nel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v1 3/5] driver core: Allow fwnode_operations.add_links to
 differentiate errors

Hi Rafael,

Thanks for the review.

On Tue, Nov 5, 2019 at 2:43 PM Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>
> On Monday, October 28, 2019 11:00:24 PM CET Saravana Kannan wrote:
> > When add_links() still has suppliers that it needs to link to in the
> > future, this patch allows it to differentiate between suppliers that are
> > needed for probing vs suppliers that are needed for sync_state()
> > correctness.
>
> I guess you mean that it will return different error codes in the different
> cases.

Yes.

>
> > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> > ---
> >  drivers/base/core.c    | 12 ++++++++----
> >  include/linux/fwnode.h | 13 +++++++++----
> >  2 files changed, 17 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index 48cd43a91ce6..e6d3e6d485da 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -2297,7 +2297,7 @@ int device_add(struct device *dev)
> >       struct device *parent;
> >       struct kobject *kobj;
> >       struct class_interface *class_intf;
> > -     int error = -EINVAL;
> > +     int error = -EINVAL, fw_ret;
> >       struct kobject *glue_dir = NULL;
> >
> >       dev = get_device(dev);
> > @@ -2413,9 +2413,13 @@ int device_add(struct device *dev)
> >        */
> >       device_link_add_missing_supplier_links();
> >
> > -     if (fwnode_has_op(dev->fwnode, add_links)
> > -         && fwnode_call_int_op(dev->fwnode, add_links, dev))
> > -             device_link_wait_for_mandatory_supplier(dev, true);
> > +     if (fwnode_has_op(dev->fwnode, add_links)) {
>
> fw_ret can be defined here and I'd just call it "ret".

I thought that style of variable declaration is frowned up in the
kernel coding style.

>
> > +             fw_ret = fwnode_call_int_op(dev->fwnode, add_links, dev);
> > +             if (fw_ret == -ENODEV)
> > +                     device_link_wait_for_mandatory_supplier(dev);
> > +             else if (fw_ret)
> > +                     device_link_wait_for_optional_supplier(dev);
> > +     }
> >
> >       bus_probe_device(dev);
> >       if (parent)
> > diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h
> > index 25bb81f8ded8..a19134eae5a5 100644
> > --- a/include/linux/fwnode.h
> > +++ b/include/linux/fwnode.h
> > @@ -96,10 +96,15 @@ struct fwnode_reference_args {
> >   *           available suppliers.
> >   *
> >   *           Return 0 if device links have been successfully created to all
> > - *           the suppliers of this device or if the supplier information is
> > - *           not known. Return an error if and only if the supplier
> > - *           information is known but some of the suppliers are not yet
> > - *           available to create device links to.
> > + *           the suppliers this device needs to create device links to or if
> > + *           the supplier information is not known.
>
> "the known suppliers of this device or if the supplier information is not known."

"suppliers it needs to create device links to" is a subset of known
suppliers. There's no requirement that fw needs to create links to ALL
known suppliers. Just a minor distinction.

> > + *
> > + *           Return -ENODEV if and only if the suppliers needed for probing
> > + *           the device are not yet available to create device links to.
>
> It would be more precise to say something like this:
>
> "Return -ENODEV if an attempt to create a device link to one of the device's
> suppliers needed for probing it fails."

"attempt to create a device link to one of the device's suppliers
needed for probing it fails" to me means device_link_add() fails.
But I'm trying to say that it should return an error if the struct
device isn't even there yet.

> > + *
> > + *           Return -EAGAIN if there are suppliers that need to be linked to
> > + *           that are not yet available but none of those suppliers are
> > + *           necessary for probing this device.
>
> "Return -EAGAIN if attempts to create device links to some of the device's
> suppliers have failed, but those suppliers are not necessary for probing the
> device."

Same comment as before. The distinction I'm making here is that
-EAGAIN is needed when the struct device itself isn't there.

Btw, Greg already pulled these into driver-core-next. Let me know if
you want me to send a delta patch to fix any of these comments.

Thanks,
Saravana