Re: [PATCH v6 04/22] of: add function to allow probing a device from a OF node

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

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.