linux-kernel - Re: [PATCH v6 03/22] of/platform: Point to struct device from device node

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Message-ID: <1806288.pmhamH8mKQ@vostro.rjw.lan>
Date:	Sat, 24 Oct 2015 15:57:24 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
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 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?

Thanks,
Rafael

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