On Sat, Jul 20, 2019 at 12:17 AM Saravana Kannan <saravanak@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
> .../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
>
