Date:   Thu, 5 Nov 2020 23:41:20 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.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>,
        Android Kernel Team <kernel-team@...roid.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v1 15/18] of: property: Update implementation of
 add_links() to create fwnode links

On Thu, Nov 5, 2020 at 11:22 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Thu, Nov 05, 2020 at 03:25:56PM -0800, Saravana Kannan wrote:
> > On Thu, Nov 5, 2020 at 1:41 AM Greg Kroah-Hartman
> > <gregkh@...uxfoundation.org> wrote:
> > >
> > > On Wed, Nov 04, 2020 at 03:23:52PM -0800, Saravana Kannan wrote:
> > > > The semantics of add_links() has changed from creating device link
> > > > between devices to creating fwnode links between fwnodes. So, update the
> > > > implementation of add_links() to match the new semantics.
> > > >
> > > > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> > > > ---
> > > >  drivers/of/property.c | 150 ++++++++++++------------------------------
> > > >  1 file changed, 41 insertions(+), 109 deletions(-)
> > > >
> > > > diff --git a/drivers/of/property.c b/drivers/of/property.c
> > > > index 408a7b5f06a9..86303803f1b3 100644
> > > > --- a/drivers/of/property.c
> > > > +++ b/drivers/of/property.c
> > > > @@ -1038,33 +1038,9 @@ static bool of_is_ancestor_of(struct device_node *test_ancestor,
> > > >  }
> > > >
> > > >  /**
> > > > - * of_get_next_parent_dev - Add device link to supplier from supplier phandle
> > > > - * @np: device tree node
> > > > - *
> > > > - * Given a device tree node (@np), this function finds its closest ancestor
> > > > - * device tree node that has a corresponding struct device.
> > > > - *
> > > > - * The caller of this function is expected to call put_device() on the returned
> > > > - * device when they are done.
> > > > - */
> > > > -static struct device *of_get_next_parent_dev(struct device_node *np)
> > > > -{
> > > > -     struct device *dev = NULL;
> > > > -
> > > > -     of_node_get(np);
> > > > -     do {
> > > > -             np = of_get_next_parent(np);
> > > > -             if (np)
> > > > -                     dev = get_dev_from_fwnode(&np->fwnode);
> > > > -     } while (np && !dev);
> > > > -     of_node_put(np);
> > > > -     return dev;
> > > > -}
> > > > -
> > > > -/**
> > > > - * of_link_to_phandle - Add device link to supplier from supplier phandle
> > > > - * @dev: consumer device
> > > > - * @sup_np: phandle to supplier device tree node
> > > > + * of_link_to_phandle - Add fwnode link to supplier from supplier phandle
> > > > + * @con_np: consumer device tree node
> > > > + * @sup_np: supplier device tree node
> > > >   *
> > > >   * Given a phandle to a supplier device tree node (@sup_np), this function
> > > >   * finds the device that owns the supplier device tree node and creates a
> > > > @@ -1074,16 +1050,14 @@ static struct device *of_get_next_parent_dev(struct device_node *np)
> > > >   * cases, it returns an error.
> > > >   *
> > > >   * Returns:
> > > > - * - 0 if link successfully created to supplier
> > > > - * - -EAGAIN if linking to the supplier should be reattempted
> > > > + * - 0 if fwnode link successfully created to supplier
> > > >   * - -EINVAL if the supplier link is invalid and should not be created
> > > > - * - -ENODEV if there is no device that corresponds to the supplier phandle
> > > > + * - -ENODEV if struct device will never be create for supplier
> > > >   */
> > > > -static int of_link_to_phandle(struct device *dev, struct device_node *sup_np,
> > > > -                           u32 dl_flags)
> > > > +static int of_link_to_phandle(struct device_node *con_np,
> > > > +                           struct device_node *sup_np)
> > > >  {
> > > > -     struct device *sup_dev, *sup_par_dev;
> > > > -     int ret = 0;
> > > > +     struct device *sup_dev;
> > > >       struct device_node *tmp_np = sup_np;
> > > >
> > > >       of_node_get(sup_np);
> > > > @@ -1106,7 +1080,8 @@ static int of_link_to_phandle(struct device *dev, struct device_node *sup_np,
> > > >       }
> > > >
> > > >       if (!sup_np) {
> > > > -             dev_dbg(dev, "Not linking to %pOFP - No device\n", tmp_np);
> > > > +             pr_debug("Not linking %pOFP to %pOFP - No device\n",
> > > > +                      con_np, tmp_np);
> > >
> > > Who is calling this function without a valid dev pointer?
> >
> > Sorry, I plan to delete the "dev" parameter as it's not really used
> > anywhere. I'm trying to do that without causing build time errors and
> > making the series into digestible small patches.
> >
> > I can do the deletion of the parameter as a Patch 19/19. Will that work?
>
> That's fine, but why get rid of dev?  The driver core works on these
> things, and we want errors/messages/warnings to spit out what device is
> causing those issues.  It is fine to drag around a struct device pointer
> just for messages, that's to be expected, and is good.

In general I agree. If the fwnode being parsed is related to the dev,
it's nice to have the dev name in the logs.

But in this instance I feel it's analogous to printing the PID that's
parsing the fwnode -- kinda irrelevant. The device in question can
appear very random and it'll just cause more confusion than be of help
if it shows up in the logs.

For example it can be something like:
<gpio device name>: linking <wifi fwnode> to <iommu fwnode>

If the device was actually that of the wifi fwnode of the iommu
fwnode, I agree it'll be useful to carry around the dev even if it's
just for logs.

Hope that makes sense.

> > > And the only way it can be NULL is if fwnode is NULL, and as you control
> > > the callers to it, how can that be the case?
> >
> > fwnode represents a generic firmware node. The to_of_node() returns
> > NULL if fwnode is not a DT node. So con_np can be NULL if that
> > happens. That's why we need a NULL check here.  With the current code,
> > that can never happen, bit I think it doesn't hurt to check in case
> > there's a buggy caller. I don't have a strong opinion - so I can do it
> > whichever way.
>
> If it can't happen, no need to check for it :)

I don't have a strong opinion, so I can delete it if you insist.

-Saravana

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