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Message-ID: <CAAObsKBjNZMhKn2bUMmQO8Lvrqfucnf9dXqmbfQ2DbAc6_GvcQ@mail.gmail.com>
Date: Tue, 27 Oct 2015 15:48:40 +0100
From: Tomeu Vizoso <tomeu.vizoso@...labora.com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc: "linux-kernel@...r.kernel.org" <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"
<linux-arm-kernel@...ts.infradead.org>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
Linus Walleij <linus.walleij@...aro.org>,
linux-acpi@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v6 03/22] of/platform: Point to struct device from device node
On 24 October 2015 at 15:57, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> On Thursday, October 22, 2015 03:01:45 PM Tomeu Vizoso wrote:
>> On 22 October 2015 at 03:02, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
>> > On Monday, September 21, 2015 04:02:43 PM Tomeu Vizoso wrote:
>> >> When adding platform and AMBA devices, set the device node's device
>> >> member to point to it.
>> >>
>> >> This speeds lookups considerably and is safe because we only create one
>> >> of these devices for any given device node.
>> >>
>> >> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
>> >> ---
>> >>
>> >> Changes in v5:
>> >> - Set the pointer to struct device also for AMBA devices
>> >> - Unset the pointer to struct device when the platform device is about
>> >> to be unregistered
>> >> - Increase the reference count of the device before returning from
>> >> of_find_device_by_node()
>> >>
>> >> drivers/of/platform.c | 19 ++++++++++---------
>> >> include/linux/of.h | 1 +
>> >> 2 files changed, 11 insertions(+), 9 deletions(-)
>> >>
>> >> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
>> >> index 1001efaedcb8..408d89f1d124 100644
>> >> --- a/drivers/of/platform.c
>> >> +++ b/drivers/of/platform.c
>> >> @@ -32,11 +32,6 @@ const struct of_device_id of_default_bus_match_table[] = {
>> >> {} /* Empty terminated list */
>> >> };
>> >>
>> >> -static int of_dev_node_match(struct device *dev, void *data)
>> >> -{
>> >> - return dev->of_node == data;
>> >> -}
>> >> -
>> >> /**
>> >> * of_find_device_by_node - Find the platform_device associated with a node
>> >> * @np: Pointer to device tree node
>> >> @@ -45,10 +40,10 @@ static int of_dev_node_match(struct device *dev, void *data)
>> >> */
>> >> struct platform_device *of_find_device_by_node(struct device_node *np)
>> >> {
>> >> - struct device *dev;
>> >> -
>> >> - dev = bus_find_device(&platform_bus_type, NULL, np, of_dev_node_match);
>> >> - return dev ? to_platform_device(dev) : NULL;
>> >> + if (np->device && np->device->bus == &platform_bus_type &&
>> >> + get_device(np->device))
>> >> + return to_platform_device(np->device);
>> >> + return NULL;
>> >> }
>> >> EXPORT_SYMBOL(of_find_device_by_node);
>> >>
>> >> @@ -192,6 +187,8 @@ static struct platform_device *of_platform_device_create_pdata(
>> >> goto err_clear_flag;
>> >> }
>> >>
>> >> + np->device = &dev->dev;
>> >> +
>> >> return dev;
>> >>
>> >> err_clear_flag:
>> >> @@ -272,6 +269,8 @@ static struct amba_device *of_amba_device_create(struct device_node *node,
>> >> goto err_free;
>> >> }
>> >>
>> >> + node->device = &dev->dev;
>> >> +
>> >> return dev;
>> >>
>> >> err_free:
>> >> @@ -476,6 +475,8 @@ static int of_platform_device_destroy(struct device *dev, void *data)
>> >> if (of_node_check_flag(dev->of_node, OF_POPULATED_BUS))
>> >> device_for_each_child(dev, NULL, of_platform_device_destroy);
>> >>
>> >> + dev->of_node->device = NULL;
>> >> +
>> >> if (dev->bus == &platform_bus_type)
>> >> platform_device_unregister(to_platform_device(dev));
>> >> #ifdef CONFIG_ARM_AMBA
>> >> diff --git a/include/linux/of.h b/include/linux/of.h
>> >> index 2194b8ca41f9..eb091be0f8ee 100644
>> >> --- a/include/linux/of.h
>> >> +++ b/include/linux/of.h
>> >> @@ -52,6 +52,7 @@ struct device_node {
>> >> phandle phandle;
>> >> const char *full_name;
>> >> struct fwnode_handle fwnode;
>> >> + struct device *device;
>> >
>> > There are cases in which multiple device objects point to the same device_node,
>> > so is the single struct device pointer here really sufficient?
>>
>> Only one struct device is registered for a given DT device node when
>> the DT is scanned (otherwise, of_find_device_by_node wouldn't be
>> safe).
>>
>> If some driver makes a struct device to point to a device_node that
>> already has a struct device associated with it, that's fine.
>
> Well, once that has happened, your new device pointer in the given device_node
> becomes useless. Why exactly is that fine?
Why do you think it's useless? It's the device that was registered
from that device_node. The other one just happens to want to point to
the same device_node for whatever other reason, but I don't see how is
that relevant.
Regards,
Tomeu
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