linux-kernel - Re: [PATCH v1 17/18] driver core: Add helper functions to convert fwnode links to device links

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Date:   Fri, 20 Nov 2020 18:00:43 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v1 17/18] driver core: Add helper functions to convert
 fwnode links to device links

On Mon, Nov 16, 2020 at 8:57 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Nov 5, 2020 at 12:24 AM Saravana Kannan <saravanak@...gle.com> wrote:
> >
> > Add helper functions __fw_devlink_link_to_consumers() and
> > __fw_devlink_link_to_suppliers() that convert fwnode links to device
> > links.
> >
> > __fw_devlink_link_to_consumers() is for creating:
> > - Device links between a newly added device and all its consumer devices
> >   that have been added to driver core.
> > - Proxy SYNC_STATE_ONLY device links between the newly added device and
> >   the parent devices of all its consumers that have not been added to
> >   driver core yet.
> >
> > __fw_devlink_link_to_suppliers() is for creating:
> > - Device links between a newly added device and all its supplier devices
> > - Proxy SYNC_STATE_ONLY device links between the newly added device and
> >   all the supplier devices of its child device nodes.
> >
> > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> > ---
> >  drivers/base/core.c | 228 ++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 228 insertions(+)
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index d51dd564add1..0c87ff949d81 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -1585,6 +1585,234 @@ static struct device *fwnode_get_next_parent_dev(struct fwnode_handle *fwnode)
> >         return dev;
> >  }
> >
> > +/**
> > + * fw_devlink_create_devlink - Create a device link from a consumer to fwnode
>
> Have you considered renaming "fw_devlink" to "fwnode_link"?

I avoided using fwnode_link prefix because it's not related to the
fwnode link APIs. This is a fw_devlink feature related code and hence
the fw_devlink prefix.

I could just call it fw_devlink_create() or fw_devlink_create_links()
or fwnode_to_dev_link() if that's less confusing. Any preferences?

> That would be much less confusing IMO and the name of this function
> would be clearer.
>
> > + * @con - Consumer device for the device link
> > + * @sup - fwnode handle of supplier
> > + *
> > + * This function will try to create a device link between the consumer and the
> > + * supplier devices.
>
> "... between consumer device @con and the supplier device represented
> by @sup" (and see below).
>
> > + *
> > + * The supplier has to be provided as a fwnode because incorrect cycles in
> > + * fwnode links can sometimes cause the supplier device to never be created.
> > + * This function detects such cases and returns an error if a device link being
> > + * created in invalid.
>
> "... returns an error if it cannot create a device link from the
> consumer to a missing supplier."
>
> > + *
> > + * Returns,
> > + * 0 on successfully creating a device link
> > + * -EINVAL if the device link being attempted is invalid
>
> "if the device link cannot be created as expected"
>
> > + * -EAGAIN if the device link needs to be attempted again in the future
>
> "if the device link cannot be created right now, but it may be
> possible to do that in the future."

Ack to all the documentation comments above.

>
> > + */
> > +static int fw_devlink_create_devlink(struct device *con,
> > +                                    struct fwnode_handle *sup, u32 flags)
>
> I'd call the second arg sup_handle to indicate that it is not a struct device.

Ack

>
> > +{
> > +       struct device *sup_dev, *sup_par_dev;
> > +       int ret = 0;
> > +
> > +       sup_dev = get_dev_from_fwnode(sup);
> > +       /*
> > +        * If we can't find the supplier device from its fwnode, it might be
> > +        * due to a cyclic dependcy between fwnodes. Some of these cycles can
>
> dependency
>

Ack

> > +        * be broken by applying logic. Check for these types of cycles and
> > +        * break them so that devices in the cycle probe properly.
> > +        */
>
> I would do
>
> if (sup_dev) {
>         if (!device_link_add(con, sup_dev, flags))
>                 ret = -EINVAL;
>
>         put_device(sup_dev);
>         return ret;
> }
>
> here and the cycle detection (error code path) below, possibly using
> the same dev pointer.

Nice suggestion, thanks!


-Saravana