linux-kernel - Re: [PATCH v11 3/6] of: property: Add functional dependency link from DT bindings

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Message-Id: <20191008145304.2BD54205F4@mail.kernel.org>
Date:   Tue, 08 Oct 2019 07:53:02 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Jonathan Corbet <corbet@....net>, Len Brown <lenb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Saravana Kannan <saravanak@...gle.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-acpi@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        David Collins <collinsd@...eaurora.org>,
        kernel-team@...roid.com, kbuild test robot <lkp@...el.com>
Subject: Re: [PATCH v11 3/6] of: property: Add functional dependency link from DT bindings

Quoting Greg Kroah-Hartman (2019-10-04 08:37:50)
> On Wed, Sep 11, 2019 at 03:29:25AM -0700, Stephen Boyd wrote:
> > Quoting Saravana Kannan (2019-09-04 14:11:22)
> > > +       int ret = 0;
> > > +       struct device_node *tmp_np = sup_np;
> > > +
> > > +       of_node_get(sup_np);
> > > +       /*
> > > +        * Find the device node that contains the supplier phandle.  It may be
> > > +        * @sup_np or it may be an ancestor of @sup_np.
> > > +        */
> > > +       while (sup_np && !of_find_property(sup_np, "compatible", NULL))
> > > +               sup_np = of_get_next_parent(sup_np);
> > 
> > I don't get this. This is assuming that drivers are only probed for
> > device nodes that have a compatible string? What about drivers that make
> > sub-devices for clk support that have drivers in drivers/clk/ that then
> > attach at runtime later? This happens sometimes for MFDs that want to
> > split the functionality across the driver tree to the respective
> > subsystems.
> 
> For that, the link would not be there, correct?

The parent device (MFD) would have the links because that is the device
node with the provider property like '#clock-cells'. The child clk
device that's populated by the MFD would be the one actually providing
the clk via a driver that may probe any time later, or never, depending
on if the clk driver is configured as a module or not. I fail to see how
this will work for these cases.

Is this logic there to find the parent of a regulator phandle and match
that to some driver? It looks like it.

> 
> > > +static int of_link_property(struct device *dev, struct device_node *con_np,
> > > +                            const char *prop_name)
> > > +{
> > > +       struct device_node *phandle;
> > > +       const struct supplier_bindings *s = bindings;
> > > +       unsigned int i = 0;
> > > +       bool matched = false;
> > > +       int ret = 0;
> > > +
> > > +       /* Do not stop at first failed link, link all available suppliers. */
> > > +       while (!matched && s->parse_prop) {
> > > +               while ((phandle = s->parse_prop(con_np, prop_name, i))) {
> > > +                       matched = true;
> > > +                       i++;
> > > +                       if (of_link_to_phandle(dev, phandle) == -EAGAIN)
> > > +                               ret = -EAGAIN;
> > 
> > And don't break?
> 
> There was comments before about how this is not needed.  Frank asked
> that the comment be removed.  And now you point it out again :)
> 
> Look at the comment a few lines up, we have to go through all of the
> suppliers.
> 

Ok. The comment tells me what is happening but it misses the essential
part which is _why_ we must make links to each supplier and return
-EAGAIN.