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    SubjectRe: [PATCH v6 04/22] of: add function to allow probing a device from a OF node
    Date
    On Monday, September 21, 2015 04:02:44 PM Tomeu Vizoso wrote:
    > Walks the OF tree up and finds the closest ancestor that has a struct
    > device associated with it, probing it if isn't bound to a driver yet.
    >
    > The above should ensure that the dependency represented by the passed OF
    > node is available, because probing a device should cause its descendants
    > to be probed as well (when they get registered).
    >
    > Subsystems can use this when looking up resources for drivers, to reduce
    > the chances of deferred probes because of the probing order of devices.
    >
    > Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
    > ---
    >
    > Changes in v5:
    > - Move the assignment to device_node->device for AMBA devices to another
    > commit.
    > - Hold a reference to the struct device while it's in use in
    > of_device_probe().
    >
    > Changes in v4:
    > - Rename of_platform_probe to of_device_probe
    > - Use device_node.device instead of device_node.platform_dev
    >
    > Changes in v3:
    > - Set and use device_node.platform_dev instead of reversing the logic to
    > find the platform device that encloses a device node.
    > - Drop the fwnode API to probe firmware nodes and add OF-only API for
    > now. I think this same scheme could be used for machines with ACPI,
    > but I haven't been able to find one that had to defer its probes because
    > of the device probe order.
    >
    > drivers/of/device.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++
    > include/linux/of_device.h | 3 +++
    > 2 files changed, 64 insertions(+)
    >
    > diff --git a/drivers/of/device.c b/drivers/of/device.c
    > index 8b91ea241b10..836be71fc90e 100644
    > --- a/drivers/of/device.c
    > +++ b/drivers/of/device.c
    > @@ -286,3 +286,64 @@ int of_device_uevent_modalias(struct device *dev, struct kobj_uevent_env *env)
    >
    > return 0;
    > }
    > +
    > +/**
    > + * of_device_probe() - Probe device associated with OF node
    > + * @np: node to probe
    > + *
    > + * Probe the device associated with the passed device node.
    > + */
    > +void of_device_probe(struct device_node *np)

    Same question as from Greg: How does a subsystem know whether or not to use
    this function?

    > +{
    > + struct device_node *target;
    > + struct device *dev = NULL;
    > +
    > + if (!of_root || !of_node_check_flag(of_root, OF_POPULATED_BUS))
    > + return;
    > +
    > + if (!np)
    > + return;
    > +
    > + of_node_get(np);
    > +
    > + /* Find the closest ancestor that has a device associated */
    > + for (target = np;
    > + !of_node_is_root(target);
    > + target = of_get_next_parent(target))
    > + if (get_device(target->device)) {
    > + dev = target->device;
    > + break;
    > + }
    > +
    > + of_node_put(target);
    > +
    > + if (!dev) {
    > + pr_warn("Couldn't find a device for node '%s'\n",
    > + of_node_full_name(np));
    > + return;
    > + }
    > +
    > + /*
    > + * Device is bound or is being probed right now. If we have bad luck
    > + * and the dependency isn't ready when it's needed, deferred probe
    > + * will save us.
    > + */
    > + if (dev->driver)
    > + goto out;
    > +
    > + /*
    > + * Probing a device should cause its descendants to be probed as
    > + * well, which includes the passed device node.
    > + */
    > + if (device_attach(dev) != 1)
    > + /*
    > + * This cannot be a warning for now because clock nodes have a
    > + * compatible string but the clock framework doesn't follow
    > + * the device/driver model yet.
    > + */
    > + dev_dbg(dev, "Probe failed for %s\n", of_node_full_name(np));
    > +
    > +out:
    > + put_device(dev);
    > +}
    > +EXPORT_SYMBOL_GPL(of_device_probe);
    > diff --git a/include/linux/of_device.h b/include/linux/of_device.h
    > index cc7dd687a89d..da8d489e73ad 100644
    > --- a/include/linux/of_device.h
    > +++ b/include/linux/of_device.h
    > @@ -40,6 +40,7 @@ extern ssize_t of_device_get_modalias(struct device *dev,
    >
    > extern void of_device_uevent(struct device *dev, struct kobj_uevent_env *env);
    > extern int of_device_uevent_modalias(struct device *dev, struct kobj_uevent_env *env);
    > +extern void of_device_probe(struct device_node *np);
    >
    > static inline void of_device_node_put(struct device *dev)
    > {
    > @@ -84,6 +85,8 @@ static inline int of_device_uevent_modalias(struct device *dev,
    > return -ENODEV;
    > }
    >
    > +static inline void of_device_probe(struct device_node *np) { }
    > +
    > static inline void of_device_node_put(struct device *dev) { }
    >
    > static inline const struct of_device_id *__of_match_device(
    >

    --
    I speak only for myself.
    Rafael J. Wysocki, Intel Open Source Technology Center.


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