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Date: Thu, 22 Oct 2015 03:06:47 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc: linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
Stephen Warren <swarren@...dotorg.org>,
Javier Martinez Canillas <javier@....samsung.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Mark Brown <broonie@...nel.org>,
Thierry Reding <thierry.reding@...il.com>,
Alan Stern <stern@...land.harvard.edu>,
linux-arm-kernel@...ts.infradead.org,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
devicetree@...r.kernel.org,
Linus Walleij <linus.walleij@...aro.org>,
linux-acpi@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v6 04/22] of: add function to allow probing a device from a OF node
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@...labora.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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