[PATCH v6 3/7] of/platform: Add functional dependency link from DT bindings

[PATCH v6 3/7] of/platform: Add functional dependency link from DT bindings

[Saravana Kannan]

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. This leads to downstream hacks to handle cases like this
  that can easily be solved in the upstream kernel.

  By linking devices before they are probed, we give suppliers a clear
  count of the number of dependent consumers. Once all of the
  consumers are active, the suppliers can turn off the unused
  resources without making assumptions about the number of consumers.

By default we just add device-links to track "driver presence" (probe
succeeded) of the supplier device. If any other functionality provided
by device-links are needed, it is left to the consumer/supplier
devices to change the link when they probe.

Signed-off-by: Saravana Kannan <saravanak@google.com>
---
 .../admin-guide/kernel-parameters.txt         |   5 +
 drivers/of/platform.c                         | 158 ++++++++++++++++++
 2 files changed, 163 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 138f6664b2e2..109b4310844f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3141,6 +3141,11 @@
 			This can be set from sysctl after boot.
 			See Documentation/sysctl/vm.txt for details.
 
+	of_devlink	[KNL] Make device links from common DT bindings. Useful
+			for optimizing probe order and making sure resources
+			aren't turned off before the consumer devices have
+			probed.
+
 	ohci1394_dma=early	[HW] enable debugging via the ohci1394 driver.
 			See Documentation/debugging-via-ohci1394.txt for more
 			info.
diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index 04ad312fd85b..88a2086e26fa 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -509,6 +509,163 @@ int of_platform_default_populate(struct device_node *root,
 }
 EXPORT_SYMBOL_GPL(of_platform_default_populate);
 
+bool of_link_is_valid(struct device_node *con, struct device_node *sup)
+{
+	of_node_get(sup);
+	/*
+	 * Don't allow linking a device node as a consumer of one of its
+	 * descendant nodes. By definition, a child node can't be a functional
+	 * dependency for the parent node.
+	 */
+	while (sup) {
+		if (sup == con) {
+			of_node_put(sup);
+			return false;
+		}
+		sup = of_get_next_parent(sup);
+	}
+	return true;
+}
+
+static int of_link_to_phandle(struct device *dev, struct device_node *sup_np)
+{
+	struct platform_device *sup_dev;
+	u32 dl_flags = DL_FLAG_AUTOPROBE_CONSUMER;
+	int ret = 0;
+
+	/*
+	 * Since we are trying to create device links, we need to find
+	 * the actual device node that owns this supplier phandle.
+	 * Often times it's the same node, but sometimes it can be one
+	 * of the parents. So walk up the parent till you find a
+	 * device.
+	 */
+	while (sup_np && !of_find_property(sup_np, "compatible", NULL))
+		sup_np = of_get_next_parent(sup_np);
+	if (!sup_np)
+		return 0;
+
+	if (!of_link_is_valid(dev->of_node, sup_np)) {
+		of_node_put(sup_np);
+		return 0;
+	}
+	sup_dev = of_find_device_by_node(sup_np);
+	of_node_put(sup_np);
+	if (!sup_dev)
+		return -ENODEV;
+	if (!device_link_add(dev, &sup_dev->dev, dl_flags))
+		ret = -ENODEV;
+	put_device(&sup_dev->dev);
+	return ret;
+}
+
+static struct device_node *parse_prop_cells(struct device_node *np,
+					    const char *prop, int i,
+					    const char *binding,
+					    const char *cell)
+{
+	struct of_phandle_args sup_args;
+
+	if (!i && strcmp(prop, binding))
+		return NULL;
+
+	if (of_parse_phandle_with_args(np, binding, cell, i, &sup_args))
+		return NULL;
+
+	return sup_args.np;
+}
+
+static struct device_node *parse_clocks(struct device_node *np,
+					const char *prop, int i)
+{
+	return parse_prop_cells(np, prop, i, "clocks", "#clock-cells");
+}
+
+static struct device_node *parse_interconnects(struct device_node *np,
+					       const char *prop, int i)
+{
+	return parse_prop_cells(np, prop, i, "interconnects",
+				"#interconnect-cells");
+}
+
+static int strcmp_suffix(const char *str, const char *suffix)
+{
+	unsigned int len, suffix_len;
+
+	len = strlen(str);
+	suffix_len = strlen(suffix);
+	if (len <= suffix_len)
+		return -1;
+	return strcmp(str + len - suffix_len, suffix);
+}
+
+static struct device_node *parse_regulators(struct device_node *np,
+					    const char *prop, int i)
+{
+	if (i || strcmp_suffix(prop, "-supply"))
+		return NULL;
+
+	return of_parse_phandle(np, prop, 0);
+}
+
+/**
+ * struct supplier_bindings - Information for parsing supplier DT binding
+ *
+ * @parse_prop:		If the function cannot parse the property, return NULL.
+ *			Otherwise, return the phandle listed in the property
+ *			that corresponds to index i.
+ */
+struct supplier_bindings {
+	struct device_node *(*parse_prop)(struct device_node *np,
+					  const char *name, int i);
+};
+
+struct supplier_bindings bindings[] = {
+	{ .parse_prop = parse_clocks, },
+	{ .parse_prop = parse_interconnects, },
+	{ .parse_prop = parse_regulators, },
+	{ },
+};
+
+static bool of_link_property(struct device *dev, struct device_node *con_np,
+			     const char *prop)
+{
+	struct device_node *phandle;
+	struct supplier_bindings *s = bindings;
+	unsigned int i = 0;
+	bool done = true;
+
+	while (!i && s->parse_prop) {
+		while ((phandle = s->parse_prop(con_np, prop, i))) {
+			i++;
+			if (of_link_to_phandle(dev, phandle))
+				done = false;
+		}
+		s++;
+	}
+	return done ? 0 : -ENODEV;
+}
+
+static bool of_devlink;
+core_param(of_devlink, of_devlink, bool, 0);
+
+static int of_link_to_suppliers(struct device *dev)
+{
+	struct property *p;
+	bool done = true;
+
+	if (!of_devlink)
+		return 0;
+	if (unlikely(!dev->of_node))
+		return 0;
+
+	for_each_property_of_node(dev->of_node, p)
+		if (of_link_property(dev, dev->of_node, p->name))
+			done = false;
+
+	return done ? 0 : -ENODEV;
+}
+
 #ifndef CONFIG_PPC
 static const struct of_device_id reserved_mem_matches[] = {
 	{ .compatible = "qcom,rmtfs-mem" },
@@ -524,6 +681,7 @@ static int __init of_platform_default_populate_init(void)
 	if (!of_have_populated_dt())
 		return -ENODEV;
 
+	platform_bus_type.add_links = of_link_to_suppliers;
 	/*
 	 * Handle certain compatibles explicitly, since we don't want to create
 	 * platform_devices for every node in /reserved-memory with a
-- 
2.22.0.657.g960e92d24f-goog

Re: [PATCH v6 3/7] of/platform: Add functional dependency link from DT bindings

[Rob Herring]

On Sat, Jul 20, 2019 at 12:17 AM Saravana Kannan <saravanak@google.com> wrote:
>
> Add device-links after the devices are created (but before they are
> probed) by looking at common DT bindings like clocks and
> interconnects.

The structure now looks a lot better to me. A few minor things below.

>
> 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. This leads to downstream hacks to handle cases like this
>   that can easily be solved in the upstream kernel.
>
>   By linking devices before they are probed, we give suppliers a clear
>   count of the number of dependent consumers. Once all of the
>   consumers are active, the suppliers can turn off the unused
>   resources without making assumptions about the number of consumers.
>
> By default we just add device-links to track "driver presence" (probe
> succeeded) of the supplier device. If any other functionality provided
> by device-links are needed, it is left to the consumer/supplier
> devices to change the link when they probe.
>
> Signed-off-by: Saravana Kannan <saravanak@google.com>
> ---
>  .../admin-guide/kernel-parameters.txt         |   5 +
>  drivers/of/platform.c                         | 158 ++++++++++++++++++
>  2 files changed, 163 insertions(+)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 138f6664b2e2..109b4310844f 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3141,6 +3141,11 @@
>                         This can be set from sysctl after boot.
>                         See Documentation/sysctl/vm.txt for details.
>
> +       of_devlink      [KNL] Make device links from common DT bindings. Useful
> +                       for optimizing probe order and making sure resources
> +                       aren't turned off before the consumer devices have
> +                       probed.
> +
>         ohci1394_dma=early      [HW] enable debugging via the ohci1394 driver.
>                         See Documentation/debugging-via-ohci1394.txt for more
>                         info.
> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> index 04ad312fd85b..88a2086e26fa 100644
> --- a/drivers/of/platform.c
> +++ b/drivers/of/platform.c
> @@ -509,6 +509,163 @@ int of_platform_default_populate(struct device_node *root,
>  }
>  EXPORT_SYMBOL_GPL(of_platform_default_populate);
>
> +bool of_link_is_valid(struct device_node *con, struct device_node *sup)
> +{
> +       of_node_get(sup);
> +       /*
> +        * Don't allow linking a device node as a consumer of one of its
> +        * descendant nodes. By definition, a child node can't be a functional
> +        * dependency for the parent node.
> +        */
> +       while (sup) {
> +               if (sup == con) {
> +                       of_node_put(sup);
> +                       return false;
> +               }
> +               sup = of_get_next_parent(sup);
> +       }
> +       return true;
> +}
> +
> +static int of_link_to_phandle(struct device *dev, struct device_node *sup_np)
> +{
> +       struct platform_device *sup_dev;
> +       u32 dl_flags = DL_FLAG_AUTOPROBE_CONSUMER;
> +       int ret = 0;
> +
> +       /*
> +        * Since we are trying to create device links, we need to find
> +        * the actual device node that owns this supplier phandle.
> +        * Often times it's the same node, but sometimes it can be one
> +        * of the parents. So walk up the parent till you find a
> +        * device.
> +        */
> +       while (sup_np && !of_find_property(sup_np, "compatible", NULL))
> +               sup_np = of_get_next_parent(sup_np);
> +       if (!sup_np)
> +               return 0;
> +
> +       if (!of_link_is_valid(dev->of_node, sup_np)) {
> +               of_node_put(sup_np);
> +               return 0;
> +       }
> +       sup_dev = of_find_device_by_node(sup_np);
> +       of_node_put(sup_np);
> +       if (!sup_dev)
> +               return -ENODEV;
> +       if (!device_link_add(dev, &sup_dev->dev, dl_flags))
> +               ret = -ENODEV;
> +       put_device(&sup_dev->dev);
> +       return ret;
> +}
> +
> +static struct device_node *parse_prop_cells(struct device_node *np,
> +                                           const char *prop, int i,

I like 'i' for for loops, but less so for function params. Perhaps
'index' instead like of_parse_phandle_with_args.

> +                                           const char *binding,
> +                                           const char *cell)
> +{
> +       struct of_phandle_args sup_args;
> +
> +       if (!i && strcmp(prop, binding))

Why the '!i' test?

> +               return NULL;
> +
> +       if (of_parse_phandle_with_args(np, binding, cell, i, &sup_args))
> +               return NULL;
> +
> +       return sup_args.np;
> +}
> +
> +static struct device_node *parse_clocks(struct device_node *np,
> +                                       const char *prop, int i)
> +{
> +       return parse_prop_cells(np, prop, i, "clocks", "#clock-cells");
> +}
> +
> +static struct device_node *parse_interconnects(struct device_node *np,
> +                                              const char *prop, int i)
> +{
> +       return parse_prop_cells(np, prop, i, "interconnects",
> +                               "#interconnect-cells");
> +}
> +
> +static int strcmp_suffix(const char *str, const char *suffix)
> +{
> +       unsigned int len, suffix_len;
> +
> +       len = strlen(str);
> +       suffix_len = strlen(suffix);
> +       if (len <= suffix_len)
> +               return -1;
> +       return strcmp(str + len - suffix_len, suffix);
> +}
> +
> +static struct device_node *parse_regulators(struct device_node *np,
> +                                           const char *prop, int i)
> +{
> +       if (i || strcmp_suffix(prop, "-supply"))
> +               return NULL;
> +
> +       return of_parse_phandle(np, prop, 0);
> +}
> +
> +/**
> + * struct supplier_bindings - Information for parsing supplier DT binding
> + *
> + * @parse_prop:                If the function cannot parse the property, return NULL.
> + *                     Otherwise, return the phandle listed in the property
> + *                     that corresponds to index i.
> + */
> +struct supplier_bindings {
> +       struct device_node *(*parse_prop)(struct device_node *np,
> +                                         const char *name, int i);
> +};
> +
> +struct supplier_bindings bindings[] = {

static const

> +       { .parse_prop = parse_clocks, },
> +       { .parse_prop = parse_interconnects, },
> +       { .parse_prop = parse_regulators, },
> +       { },
> +};
> +
> +static bool of_link_property(struct device *dev, struct device_node *con_np,
> +                            const char *prop)
> +{
> +       struct device_node *phandle;
> +       struct supplier_bindings *s = bindings;
> +       unsigned int i = 0;
> +       bool done = true;
> +
> +       while (!i && s->parse_prop) {

Using 'i' is a little odd. Perhaps a 'matched' bool would be easier to read.

> +               while ((phandle = s->parse_prop(con_np, prop, i))) {
> +                       i++;
> +                       if (of_link_to_phandle(dev, phandle))
> +                               done = false;

Just return here. No point in continuing as 'done' is never set back to true.

> +               }
> +               s++;
> +       }
> +       return done ? 0 : -ENODEV;
> +}
> +
> +static bool of_devlink;
> +core_param(of_devlink, of_devlink, bool, 0);
> +
> +static int of_link_to_suppliers(struct device *dev)
> +{
> +       struct property *p;
> +       bool done = true;
> +
> +       if (!of_devlink)
> +               return 0;
> +       if (unlikely(!dev->of_node))
> +               return 0;
> +
> +       for_each_property_of_node(dev->of_node, p)
> +               if (of_link_property(dev, dev->of_node, p->name))
> +                       done = false;
> +
> +       return done ? 0 : -ENODEV;
> +}
> +
>  #ifndef CONFIG_PPC
>  static const struct of_device_id reserved_mem_matches[] = {
>         { .compatible = "qcom,rmtfs-mem" },
> @@ -524,6 +681,7 @@ static int __init of_platform_default_populate_init(void)
>         if (!of_have_populated_dt())
>                 return -ENODEV;
>
> +       platform_bus_type.add_links = of_link_to_suppliers;
>         /*
>          * Handle certain compatibles explicitly, since we don't want to create
>          * platform_devices for every node in /reserved-memory with a
> --
> 2.22.0.657.g960e92d24f-goog
>

Re: [PATCH v6 3/7] of/platform: Add functional dependency link from DT bindings

[Saravana Kannan]

On Tue, Jul 23, 2019 at 11:06 AM Rob Herring <robh+dt@kernel.org> wrote:
>
> On Sat, Jul 20, 2019 at 12:17 AM Saravana Kannan <saravanak@google.com> wrote:
> >
> > Add device-links after the devices are created (but before they are
> > probed) by looking at common DT bindings like clocks and
> > interconnects.
>
> The structure now looks a lot better to me. A few minor things below.

Thanks.

> >
> > 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. This leads to downstream hacks to handle cases like this
> >   that can easily be solved in the upstream kernel.
> >
> >   By linking devices before they are probed, we give suppliers a clear
> >   count of the number of dependent consumers. Once all of the
> >   consumers are active, the suppliers can turn off the unused
> >   resources without making assumptions about the number of consumers.
> >
> > By default we just add device-links to track "driver presence" (probe
> > succeeded) of the supplier device. If any other functionality provided
> > by device-links are needed, it is left to the consumer/supplier
> > devices to change the link when they probe.
> >
> > Signed-off-by: Saravana Kannan <saravanak@google.com>
> > ---
> >  .../admin-guide/kernel-parameters.txt         |   5 +
> >  drivers/of/platform.c                         | 158 ++++++++++++++++++
> >  2 files changed, 163 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 138f6664b2e2..109b4310844f 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -3141,6 +3141,11 @@
> >                         This can be set from sysctl after boot.
> >                         See Documentation/sysctl/vm.txt for details.
> >
> > +       of_devlink      [KNL] Make device links from common DT bindings. Useful
> > +                       for optimizing probe order and making sure resources
> > +                       aren't turned off before the consumer devices have
> > +                       probed.
> > +
> >         ohci1394_dma=early      [HW] enable debugging via the ohci1394 driver.
> >                         See Documentation/debugging-via-ohci1394.txt for more
> >                         info.
> > diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> > index 04ad312fd85b..88a2086e26fa 100644
> > --- a/drivers/of/platform.c
> > +++ b/drivers/of/platform.c
> > @@ -509,6 +509,163 @@ int of_platform_default_populate(struct device_node *root,
> >  }
> >  EXPORT_SYMBOL_GPL(of_platform_default_populate);
> >
> > +bool of_link_is_valid(struct device_node *con, struct device_node *sup)
> > +{
> > +       of_node_get(sup);
> > +       /*
> > +        * Don't allow linking a device node as a consumer of one of its
> > +        * descendant nodes. By definition, a child node can't be a functional
> > +        * dependency for the parent node.
> > +        */
> > +       while (sup) {
> > +               if (sup == con) {
> > +                       of_node_put(sup);
> > +                       return false;
> > +               }
> > +               sup = of_get_next_parent(sup);
> > +       }
> > +       return true;
> > +}
> > +
> > +static int of_link_to_phandle(struct device *dev, struct device_node *sup_np)
> > +{
> > +       struct platform_device *sup_dev;
> > +       u32 dl_flags = DL_FLAG_AUTOPROBE_CONSUMER;
> > +       int ret = 0;
> > +
> > +       /*
> > +        * Since we are trying to create device links, we need to find
> > +        * the actual device node that owns this supplier phandle.
> > +        * Often times it's the same node, but sometimes it can be one
> > +        * of the parents. So walk up the parent till you find a
> > +        * device.
> > +        */
> > +       while (sup_np && !of_find_property(sup_np, "compatible", NULL))
> > +               sup_np = of_get_next_parent(sup_np);
> > +       if (!sup_np)
> > +               return 0;
> > +
> > +       if (!of_link_is_valid(dev->of_node, sup_np)) {
> > +               of_node_put(sup_np);
> > +               return 0;
> > +       }
> > +       sup_dev = of_find_device_by_node(sup_np);
> > +       of_node_put(sup_np);
> > +       if (!sup_dev)
> > +               return -ENODEV;
> > +       if (!device_link_add(dev, &sup_dev->dev, dl_flags))
> > +               ret = -ENODEV;
> > +       put_device(&sup_dev->dev);
> > +       return ret;
> > +}
> > +
> > +static struct device_node *parse_prop_cells(struct device_node *np,
> > +                                           const char *prop, int i,
>
> I like 'i' for for loops, but less so for function params. Perhaps
> 'index' instead like of_parse_phandle_with_args.

Sounds good.

>
> > +                                           const char *binding,
> > +                                           const char *cell)
> > +{
> > +       struct of_phandle_args sup_args;
> > +
> > +       if (!i && strcmp(prop, binding))
>
> Why the '!i' test?

To avoid a string comparison for every index. It's kinda wasteful once
the first index passes.

> > +               return NULL;
> > +
> > +       if (of_parse_phandle_with_args(np, binding, cell, i, &sup_args))
> > +               return NULL;
> > +
> > +       return sup_args.np;
> > +}
> > +
> > +static struct device_node *parse_clocks(struct device_node *np,
> > +                                       const char *prop, int i)
> > +{
> > +       return parse_prop_cells(np, prop, i, "clocks", "#clock-cells");
> > +}
> > +
> > +static struct device_node *parse_interconnects(struct device_node *np,
> > +                                              const char *prop, int i)
> > +{
> > +       return parse_prop_cells(np, prop, i, "interconnects",
> > +                               "#interconnect-cells");
> > +}
> > +
> > +static int strcmp_suffix(const char *str, const char *suffix)
> > +{
> > +       unsigned int len, suffix_len;
> > +
> > +       len = strlen(str);
> > +       suffix_len = strlen(suffix);
> > +       if (len <= suffix_len)
> > +               return -1;
> > +       return strcmp(str + len - suffix_len, suffix);
> > +}
> > +
> > +static struct device_node *parse_regulators(struct device_node *np,
> > +                                           const char *prop, int i)
> > +{
> > +       if (i || strcmp_suffix(prop, "-supply"))
> > +               return NULL;
> > +
> > +       return of_parse_phandle(np, prop, 0);
> > +}
> > +
> > +/**
> > + * struct supplier_bindings - Information for parsing supplier DT binding
> > + *
> > + * @parse_prop:                If the function cannot parse the property, return NULL.
> > + *                     Otherwise, return the phandle listed in the property
> > + *                     that corresponds to index i.
> > + */
> > +struct supplier_bindings {
> > +       struct device_node *(*parse_prop)(struct device_node *np,
> > +                                         const char *name, int i);
> > +};
> > +
> > +struct supplier_bindings bindings[] = {
>
> static const

Will do.

>
> > +       { .parse_prop = parse_clocks, },
> > +       { .parse_prop = parse_interconnects, },
> > +       { .parse_prop = parse_regulators, },
> > +       { },
> > +};
> > +
> > +static bool of_link_property(struct device *dev, struct device_node *con_np,
> > +                            const char *prop)
> > +{
> > +       struct device_node *phandle;
> > +       struct supplier_bindings *s = bindings;
> > +       unsigned int i = 0;
> > +       bool done = true;
> > +
> > +       while (!i && s->parse_prop) {
>
> Using 'i' is a little odd. Perhaps a 'matched' bool would be easier to read.

That's how I wrote it first (locally) and then redid it this way
because the bool felt very superfluous. I don't think this is that
hard to understand.

> > +               while ((phandle = s->parse_prop(con_np, prop, i))) {
> > +                       i++;
> > +                       if (of_link_to_phandle(dev, phandle))
> > +                               done = false;
>
> Just return here. No point in continuing as 'done' is never set back to true.

Actually, there is a point for this. Say Device-C depends on suppliers
Device-S1 and Device-S2 and they are listed in DT in that order.

Say, S1 gets populated after late_initcall_sync but S2 is probes way
before that. If I don't continue past a "failed linking" to S1 and
also link up to S2, then S2 will get a sync_state() callback before C
is probed. So I have to go through all possible suppliers and as many
as possible.

Let me add a comment about this somewhere in the code (probably the
header that defines the add_links() ops).

-Saravana

> > +               }
> > +               s++;
> > +       }
> > +       return done ? 0 : -ENODEV;
> > +}
> > +
> > +static bool of_devlink;
> > +core_param(of_devlink, of_devlink, bool, 0);
> > +
> > +static int of_link_to_suppliers(struct device *dev)
> > +{
> > +       struct property *p;
> > +       bool done = true;
> > +
> > +       if (!of_devlink)
> > +               return 0;
> > +       if (unlikely(!dev->of_node))
> > +               return 0;
> > +
> > +       for_each_property_of_node(dev->of_node, p)
> > +               if (of_link_property(dev, dev->of_node, p->name))
> > +                       done = false;
> > +
> > +       return done ? 0 : -ENODEV;
> > +}
> > +
> >  #ifndef CONFIG_PPC
> >  static const struct of_device_id reserved_mem_matches[] = {
> >         { .compatible = "qcom,rmtfs-mem" },
> > @@ -524,6 +681,7 @@ static int __init of_platform_default_populate_init(void)
> >         if (!of_have_populated_dt())
> >                 return -ENODEV;
> >
> > +       platform_bus_type.add_links = of_link_to_suppliers;
> >         /*
> >          * Handle certain compatibles explicitly, since we don't want to create
> >          * platform_devices for every node in /reserved-memory with a
> > --
> > 2.22.0.657.g960e92d24f-goog
> >

Re: [PATCH v6 3/7] of/platform: Add functional dependency link from DT bindings

[Rob Herring]

On Tue, Jul 23, 2019 at 2:49 PM Saravana Kannan <saravanak@google.com> wrote:
>
> On Tue, Jul 23, 2019 at 11:06 AM Rob Herring <robh+dt@kernel.org> wrote:
> >
> > On Sat, Jul 20, 2019 at 12:17 AM Saravana Kannan <saravanak@google.com> wrote:
> > >
> > > Add device-links after the devices are created (but before they are
> > > probed) by looking at common DT bindings like clocks and
> > > interconnects.
> >
> > The structure now looks a lot better to me. A few minor things below.
>
> Thanks.
>
> > >
> > > 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. This leads to downstream hacks to handle cases like this
> > >   that can easily be solved in the upstream kernel.
> > >
> > >   By linking devices before they are probed, we give suppliers a clear
> > >   count of the number of dependent consumers. Once all of the
> > >   consumers are active, the suppliers can turn off the unused
> > >   resources without making assumptions about the number of consumers.
> > >
> > > By default we just add device-links to track "driver presence" (probe
> > > succeeded) of the supplier device. If any other functionality provided
> > > by device-links are needed, it is left to the consumer/supplier
> > > devices to change the link when they probe.
> > >
> > > Signed-off-by: Saravana Kannan <saravanak@google.com>
> > > ---
> > >  .../admin-guide/kernel-parameters.txt         |   5 +
> > >  drivers/of/platform.c                         | 158 ++++++++++++++++++
> > >  2 files changed, 163 insertions(+)
> > >
> > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > > index 138f6664b2e2..109b4310844f 100644
> > > --- a/Documentation/admin-guide/kernel-parameters.txt
> > > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > > @@ -3141,6 +3141,11 @@
> > >                         This can be set from sysctl after boot.
> > >                         See Documentation/sysctl/vm.txt for details.
> > >
> > > +       of_devlink      [KNL] Make device links from common DT bindings. Useful
> > > +                       for optimizing probe order and making sure resources
> > > +                       aren't turned off before the consumer devices have
> > > +                       probed.
> > > +
> > >         ohci1394_dma=early      [HW] enable debugging via the ohci1394 driver.
> > >                         See Documentation/debugging-via-ohci1394.txt for more
> > >                         info.
> > > diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> > > index 04ad312fd85b..88a2086e26fa 100644
> > > --- a/drivers/of/platform.c
> > > +++ b/drivers/of/platform.c
> > > @@ -509,6 +509,163 @@ int of_platform_default_populate(struct device_node *root,
> > >  }
> > >  EXPORT_SYMBOL_GPL(of_platform_default_populate);
> > >
> > > +bool of_link_is_valid(struct device_node *con, struct device_node *sup)
> > > +{
> > > +       of_node_get(sup);
> > > +       /*
> > > +        * Don't allow linking a device node as a consumer of one of its
> > > +        * descendant nodes. By definition, a child node can't be a functional
> > > +        * dependency for the parent node.
> > > +        */
> > > +       while (sup) {
> > > +               if (sup == con) {
> > > +                       of_node_put(sup);
> > > +                       return false;
> > > +               }
> > > +               sup = of_get_next_parent(sup);
> > > +       }
> > > +       return true;
> > > +}
> > > +
> > > +static int of_link_to_phandle(struct device *dev, struct device_node *sup_np)
> > > +{
> > > +       struct platform_device *sup_dev;
> > > +       u32 dl_flags = DL_FLAG_AUTOPROBE_CONSUMER;
> > > +       int ret = 0;
> > > +
> > > +       /*
> > > +        * Since we are trying to create device links, we need to find
> > > +        * the actual device node that owns this supplier phandle.
> > > +        * Often times it's the same node, but sometimes it can be one
> > > +        * of the parents. So walk up the parent till you find a
> > > +        * device.
> > > +        */
> > > +       while (sup_np && !of_find_property(sup_np, "compatible", NULL))
> > > +               sup_np = of_get_next_parent(sup_np);
> > > +       if (!sup_np)
> > > +               return 0;
> > > +
> > > +       if (!of_link_is_valid(dev->of_node, sup_np)) {
> > > +               of_node_put(sup_np);
> > > +               return 0;
> > > +       }
> > > +       sup_dev = of_find_device_by_node(sup_np);
> > > +       of_node_put(sup_np);
> > > +       if (!sup_dev)
> > > +               return -ENODEV;
> > > +       if (!device_link_add(dev, &sup_dev->dev, dl_flags))
> > > +               ret = -ENODEV;
> > > +       put_device(&sup_dev->dev);
> > > +       return ret;
> > > +}
> > > +
> > > +static struct device_node *parse_prop_cells(struct device_node *np,
> > > +                                           const char *prop, int i,
> >
> > I like 'i' for for loops, but less so for function params. Perhaps
> > 'index' instead like of_parse_phandle_with_args.
>
> Sounds good.
>
> >
> > > +                                           const char *binding,
> > > +                                           const char *cell)
> > > +{
> > > +       struct of_phandle_args sup_args;
> > > +
> > > +       if (!i && strcmp(prop, binding))
> >
> > Why the '!i' test?
>
> To avoid a string comparison for every index. It's kinda wasteful once
> the first index passes.

That's not very obvious and pretty fragile though this is a static
function. Perhaps we should split to match() and parse() functions. At
least put a comment here as to what we're doing.

>
> > > +               return NULL;
> > > +
> > > +       if (of_parse_phandle_with_args(np, binding, cell, i, &sup_args))
> > > +               return NULL;
> > > +
> > > +       return sup_args.np;
> > > +}
> > > +
> > > +static struct device_node *parse_clocks(struct device_node *np,
> > > +                                       const char *prop, int i)
> > > +{
> > > +       return parse_prop_cells(np, prop, i, "clocks", "#clock-cells");
> > > +}
> > > +
> > > +static struct device_node *parse_interconnects(struct device_node *np,
> > > +                                              const char *prop, int i)
> > > +{
> > > +       return parse_prop_cells(np, prop, i, "interconnects",
> > > +                               "#interconnect-cells");
> > > +}
> > > +
> > > +static int strcmp_suffix(const char *str, const char *suffix)
> > > +{
> > > +       unsigned int len, suffix_len;
> > > +
> > > +       len = strlen(str);
> > > +       suffix_len = strlen(suffix);
> > > +       if (len <= suffix_len)
> > > +               return -1;
> > > +       return strcmp(str + len - suffix_len, suffix);
> > > +}
> > > +
> > > +static struct device_node *parse_regulators(struct device_node *np,
> > > +                                           const char *prop, int i)
> > > +{
> > > +       if (i || strcmp_suffix(prop, "-supply"))
> > > +               return NULL;
> > > +
> > > +       return of_parse_phandle(np, prop, 0);
> > > +}
> > > +
> > > +/**
> > > + * struct supplier_bindings - Information for parsing supplier DT binding
> > > + *
> > > + * @parse_prop:                If the function cannot parse the property, return NULL.
> > > + *                     Otherwise, return the phandle listed in the property
> > > + *                     that corresponds to index i.
> > > + */
> > > +struct supplier_bindings {
> > > +       struct device_node *(*parse_prop)(struct device_node *np,
> > > +                                         const char *name, int i);
> > > +};
> > > +
> > > +struct supplier_bindings bindings[] = {
> >
> > static const
>
> Will do.
>
> >
> > > +       { .parse_prop = parse_clocks, },
> > > +       { .parse_prop = parse_interconnects, },
> > > +       { .parse_prop = parse_regulators, },
> > > +       { },
> > > +};
> > > +
> > > +static bool of_link_property(struct device *dev, struct device_node *con_np,
> > > +                            const char *prop)
> > > +{
> > > +       struct device_node *phandle;
> > > +       struct supplier_bindings *s = bindings;
> > > +       unsigned int i = 0;
> > > +       bool done = true;
> > > +
> > > +       while (!i && s->parse_prop) {
> >
> > Using 'i' is a little odd. Perhaps a 'matched' bool would be easier to read.
>
> That's how I wrote it first (locally) and then redid it this way
> because the bool felt very superfluous. I don't think this is that
> hard to understand.

Alright...

> > > +               while ((phandle = s->parse_prop(con_np, prop, i))) {
> > > +                       i++;
> > > +                       if (of_link_to_phandle(dev, phandle))
> > > +                               done = false;
> >
> > Just return here. No point in continuing as 'done' is never set back to true.
>
> Actually, there is a point for this. Say Device-C depends on suppliers
> Device-S1 and Device-S2 and they are listed in DT in that order.
>
> Say, S1 gets populated after late_initcall_sync but S2 is probes way
> before that. If I don't continue past a "failed linking" to S1 and
> also link up to S2, then S2 will get a sync_state() callback before C
> is probed. So I have to go through all possible suppliers and as many
> as possible.
>
> Let me add a comment about this somewhere in the code (probably the
> header that defines the add_links() ops).

Okay, makes sense.

Rob

Re: [PATCH v6 3/7] of/platform: Add functional dependency link from DT bindings

[Saravana Kannan]

On Tue, Jul 23, 2019 at 3:18 PM Rob Herring <robh+dt@kernel.org> wrote:
>
> On Tue, Jul 23, 2019 at 2:49 PM Saravana Kannan <saravanak@google.com> wrote:
> >
> > On Tue, Jul 23, 2019 at 11:06 AM Rob Herring <robh+dt@kernel.org> wrote:
> > >
> > > On Sat, Jul 20, 2019 at 12:17 AM Saravana Kannan <saravanak@google.com> wrote:
> > > >
> > > > Add device-links after the devices are created (but before they are
> > > > probed) by looking at common DT bindings like clocks and
> > > > interconnects.
> > >
> > > The structure now looks a lot better to me. A few minor things below.
> >
> > Thanks.
> >
> > > >
> > > > 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. This leads to downstream hacks to handle cases like this
> > > >   that can easily be solved in the upstream kernel.
> > > >
> > > >   By linking devices before they are probed, we give suppliers a clear
> > > >   count of the number of dependent consumers. Once all of the
> > > >   consumers are active, the suppliers can turn off the unused
> > > >   resources without making assumptions about the number of consumers.
> > > >
> > > > By default we just add device-links to track "driver presence" (probe
> > > > succeeded) of the supplier device. If any other functionality provided
> > > > by device-links are needed, it is left to the consumer/supplier
> > > > devices to change the link when they probe.
> > > >
> > > > Signed-off-by: Saravana Kannan <saravanak@google.com>
> > > > ---
> > > >  .../admin-guide/kernel-parameters.txt         |   5 +
> > > >  drivers/of/platform.c                         | 158 ++++++++++++++++++
> > > >  2 files changed, 163 insertions(+)
> > > >
> > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > > > index 138f6664b2e2..109b4310844f 100644
> > > > --- a/Documentation/admin-guide/kernel-parameters.txt
> > > > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > > > @@ -3141,6 +3141,11 @@
> > > >                         This can be set from sysctl after boot.
> > > >                         See Documentation/sysctl/vm.txt for details.
> > > >
> > > > +       of_devlink      [KNL] Make device links from common DT bindings. Useful
> > > > +                       for optimizing probe order and making sure resources
> > > > +                       aren't turned off before the consumer devices have
> > > > +                       probed.
> > > > +
> > > >         ohci1394_dma=early      [HW] enable debugging via the ohci1394 driver.
> > > >                         See Documentation/debugging-via-ohci1394.txt for more
> > > >                         info.
> > > > diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> > > > index 04ad312fd85b..88a2086e26fa 100644
> > > > --- a/drivers/of/platform.c
> > > > +++ b/drivers/of/platform.c
> > > > @@ -509,6 +509,163 @@ int of_platform_default_populate(struct device_node *root,
> > > >  }
> > > >  EXPORT_SYMBOL_GPL(of_platform_default_populate);
> > > >
> > > > +bool of_link_is_valid(struct device_node *con, struct device_node *sup)
> > > > +{
> > > > +       of_node_get(sup);
> > > > +       /*
> > > > +        * Don't allow linking a device node as a consumer of one of its
> > > > +        * descendant nodes. By definition, a child node can't be a functional
> > > > +        * dependency for the parent node.
> > > > +        */
> > > > +       while (sup) {
> > > > +               if (sup == con) {
> > > > +                       of_node_put(sup);
> > > > +                       return false;
> > > > +               }
> > > > +               sup = of_get_next_parent(sup);
> > > > +       }
> > > > +       return true;
> > > > +}
> > > > +
> > > > +static int of_link_to_phandle(struct device *dev, struct device_node *sup_np)
> > > > +{
> > > > +       struct platform_device *sup_dev;
> > > > +       u32 dl_flags = DL_FLAG_AUTOPROBE_CONSUMER;
> > > > +       int ret = 0;
> > > > +
> > > > +       /*
> > > > +        * Since we are trying to create device links, we need to find
> > > > +        * the actual device node that owns this supplier phandle.
> > > > +        * Often times it's the same node, but sometimes it can be one
> > > > +        * of the parents. So walk up the parent till you find a
> > > > +        * device.
> > > > +        */
> > > > +       while (sup_np && !of_find_property(sup_np, "compatible", NULL))
> > > > +               sup_np = of_get_next_parent(sup_np);
> > > > +       if (!sup_np)
> > > > +               return 0;
> > > > +
> > > > +       if (!of_link_is_valid(dev->of_node, sup_np)) {
> > > > +               of_node_put(sup_np);
> > > > +               return 0;
> > > > +       }
> > > > +       sup_dev = of_find_device_by_node(sup_np);
> > > > +       of_node_put(sup_np);
> > > > +       if (!sup_dev)
> > > > +               return -ENODEV;
> > > > +       if (!device_link_add(dev, &sup_dev->dev, dl_flags))
> > > > +               ret = -ENODEV;
> > > > +       put_device(&sup_dev->dev);
> > > > +       return ret;
> > > > +}
> > > > +
> > > > +static struct device_node *parse_prop_cells(struct device_node *np,
> > > > +                                           const char *prop, int i,
> > >
> > > I like 'i' for for loops, but less so for function params. Perhaps
> > > 'index' instead like of_parse_phandle_with_args.
> >
> > Sounds good.
> >
> > >
> > > > +                                           const char *binding,
> > > > +                                           const char *cell)
> > > > +{
> > > > +       struct of_phandle_args sup_args;
> > > > +
> > > > +       if (!i && strcmp(prop, binding))
> > >
> > > Why the '!i' test?
> >
> > To avoid a string comparison for every index. It's kinda wasteful once
> > the first index passes.
>
> That's not very obvious and pretty fragile though this is a static
> function. Perhaps we should split to match() and parse() functions.

Yeah, I did think about doing this. That's why I made it a struct for
supplier_bindings instead of just an array of function pointers. But
having a parse function just for a strcmp() was creating a lot of code
noise. So went ahead and did it this way. We can keep it this way and
if we later see the need for a separate parse function, it should be
easy to do so (because it's already a struct for each binding).

> At
> least put a comment here as to what we're doing.

Done.

> >
> > > > +               return NULL;
> > > > +
> > > > +       if (of_parse_phandle_with_args(np, binding, cell, i, &sup_args))
> > > > +               return NULL;
> > > > +
> > > > +       return sup_args.np;
> > > > +}
> > > > +
> > > > +static struct device_node *parse_clocks(struct device_node *np,
> > > > +                                       const char *prop, int i)
> > > > +{
> > > > +       return parse_prop_cells(np, prop, i, "clocks", "#clock-cells");
> > > > +}
> > > > +
> > > > +static struct device_node *parse_interconnects(struct device_node *np,
> > > > +                                              const char *prop, int i)
> > > > +{
> > > > +       return parse_prop_cells(np, prop, i, "interconnects",
> > > > +                               "#interconnect-cells");
> > > > +}
> > > > +
> > > > +static int strcmp_suffix(const char *str, const char *suffix)
> > > > +{
> > > > +       unsigned int len, suffix_len;
> > > > +
> > > > +       len = strlen(str);
> > > > +       suffix_len = strlen(suffix);
> > > > +       if (len <= suffix_len)
> > > > +               return -1;
> > > > +       return strcmp(str + len - suffix_len, suffix);
> > > > +}
> > > > +
> > > > +static struct device_node *parse_regulators(struct device_node *np,
> > > > +                                           const char *prop, int i)
> > > > +{
> > > > +       if (i || strcmp_suffix(prop, "-supply"))
> > > > +               return NULL;
> > > > +
> > > > +       return of_parse_phandle(np, prop, 0);
> > > > +}
> > > > +
> > > > +/**
> > > > + * struct supplier_bindings - Information for parsing supplier DT binding
> > > > + *
> > > > + * @parse_prop:                If the function cannot parse the property, return NULL.
> > > > + *                     Otherwise, return the phandle listed in the property
> > > > + *                     that corresponds to index i.
> > > > + */
> > > > +struct supplier_bindings {
> > > > +       struct device_node *(*parse_prop)(struct device_node *np,
> > > > +                                         const char *name, int i);
> > > > +};
> > > > +
> > > > +struct supplier_bindings bindings[] = {
> > >
> > > static const
> >
> > Will do.
> >
> > >
> > > > +       { .parse_prop = parse_clocks, },
> > > > +       { .parse_prop = parse_interconnects, },
> > > > +       { .parse_prop = parse_regulators, },
> > > > +       { },
> > > > +};
> > > > +
> > > > +static bool of_link_property(struct device *dev, struct device_node *con_np,
> > > > +                            const char *prop)
> > > > +{
> > > > +       struct device_node *phandle;
> > > > +       struct supplier_bindings *s = bindings;
> > > > +       unsigned int i = 0;
> > > > +       bool done = true;
> > > > +
> > > > +       while (!i && s->parse_prop) {
> > >
> > > Using 'i' is a little odd. Perhaps a 'matched' bool would be easier to read.
> >
> > That's how I wrote it first (locally) and then redid it this way
> > because the bool felt very superfluous. I don't think this is that
> > hard to understand.
>
> Alright...

I like the name "matched" over "found" that I had used locally. So, I
actually went ahead and did this.

-Saravana

> > > > +               while ((phandle = s->parse_prop(con_np, prop, i))) {
> > > > +                       i++;
> > > > +                       if (of_link_to_phandle(dev, phandle))
> > > > +                               done = false;
> > >
> > > Just return here. No point in continuing as 'done' is never set back to true.
> >
> > Actually, there is a point for this. Say Device-C depends on suppliers
> > Device-S1 and Device-S2 and they are listed in DT in that order.
> >
> > Say, S1 gets populated after late_initcall_sync but S2 is probes way
> > before that. If I don't continue past a "failed linking" to S1 and
> > also link up to S2, then S2 will get a sync_state() callback before C
> > is probed. So I have to go through all possible suppliers and as many
> > as possible.
> >
> > Let me add a comment about this somewhere in the code (probably the
> > header that defines the add_links() ops).
>
> Okay, makes sense.
>
> Rob