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

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