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SubjectRe: [PATCH v11 3/6] of: property: Add functional dependency link from DT bindings
On Wed, Sep 11, 2019 at 03:29:25AM -0700, Stephen Boyd wrote:
> Quoting Saravana Kannan (2019-09-04 14:11:22)
> > Add device links after the devices are created (but before they are
> > probed) by looking at common DT bindings like clocks and
> > interconnects.
> >
> > Automatically adding device links for functional dependencies at the
> > framework level provides the following benefits:
> >
> > - Optimizes device probe order and avoids the useless work of
> > attempting probes of devices that will not probe successfully
> > (because their suppliers aren't present or haven't probed yet).
> >
> > For example, in a commonly available mobile SoC, registering just
> > one consumer device's driver at an initcall level earlier than the
> > supplier device's driver causes 11 failed probe attempts before the
> > consumer device probes successfully. This was with a kernel with all
> > the drivers statically compiled in. This problem gets a lot worse if
> > all the drivers are loaded as modules without direct symbol
> > dependencies.
> >
> > - Supplier devices like clock providers, interconnect providers, etc
> > need to keep the resources they provide active and at a particular
> > state(s) during boot up even if their current set of consumers don't
> > request the resource to be active. This is because the rest of the
> > consumers might not have probed yet and turning off the resource
> > before all the consumers have probed could lead to a hang or
> > undesired user experience.
> >
> > Some frameworks (Eg: regulator) handle this today by turning off
> > "unused" resources at late_initcall_sync and hoping all the devices
> > have probed by then. This is not a valid assumption for systems with
> > loadable modules. Other frameworks (Eg: clock) just don't handle
> > this due to the lack of a clear signal for when they can turn off
> > resources.
>
> The clk framework disables unused clks at late_initcall_sync. What do
> you mean clk framework doesn't turn them off because of a clear signal?

There's a number of minor things you pointed out in this review.

Saravana, can you send a follow-on patch for the minor code cleanups
like formatting and the like that was found here?

> > +static int of_link_to_phandle(struct device *dev, struct device_node *sup_np)
> > +{
> > + struct device *sup_dev;
> > + u32 dl_flags = DL_FLAG_AUTOPROBE_CONSUMER;
>
> Is it really a u32 instead of an unsigned int or unsigned long?
>
> > + 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?

> > +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.

> > +static int __of_link_to_suppliers(struct device *dev,
>
> Why the double underscore?
>
> > + struct device_node *con_np)
> > +{
> > + struct device_node *child;
> > + struct property *p;
> > + int ret = 0;
> > +
> > + for_each_property_of_node(con_np, p)
> > + if (of_link_property(dev, con_np, p->name))
> > + ret = -EAGAIN;
>
> Same comment.

Same response as above :)

thanks,

greg k-h

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