linux-kernel - Re: [RESEND PATCH v1 1/5] of/platform: Speed up of_find_device_by

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Date:   Mon, 10 Jun 2019 11:36:01 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        David Collins <collinsd@...eaurora.org>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [RESEND PATCH v1 1/5] of/platform: Speed up of_find_device_by_node()

Why are you resending this rather than replying to Frank's last
comments on the original?

On Mon, Jun 3, 2019 at 6:32 PM Saravana Kannan <saravanak@...gle.com> wrote:
>
> Add a pointer from device tree node to the device created from it.
> This allows us to find the device corresponding to a device tree node
> without having to loop through all the platform devices.
>
> However, fallback to looping through the platform devices to handle
> any devices that might set their own of_node.
>
> Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> ---
>  drivers/of/platform.c | 20 +++++++++++++++++++-
>  include/linux/of.h    |  3 +++
>  2 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> index 04ad312fd85b..1115a8d80a33 100644
> --- a/drivers/of/platform.c
> +++ b/drivers/of/platform.c
> @@ -42,6 +42,8 @@ static int of_dev_node_match(struct device *dev, void *data)
>         return dev->of_node == data;
>  }
>
> +static DEFINE_SPINLOCK(of_dev_lock);
> +
>  /**
>   * of_find_device_by_node - Find the platform_device associated with a node
>   * @np: Pointer to device tree node
> @@ -55,7 +57,18 @@ 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);
> +       /*
> +        * Spinlock needed to make sure np->dev doesn't get freed between NULL
> +        * check inside and kref count increment inside get_device(). This is
> +        * achieved by grabbing the spinlock before setting np->dev = NULL in
> +        * of_platform_device_destroy().
> +        */
> +       spin_lock(&of_dev_lock);
> +       dev = get_device(np->dev);
> +       spin_unlock(&of_dev_lock);
> +       if (!dev)
> +               dev = bus_find_device(&platform_bus_type, NULL, np,
> +                                     of_dev_node_match);
>         return dev ? to_platform_device(dev) : NULL;
>  }
>  EXPORT_SYMBOL(of_find_device_by_node);
> @@ -196,6 +209,7 @@ static struct platform_device *of_platform_device_create_pdata(
>                 platform_device_put(dev);
>                 goto err_clear_flag;
>         }
> +       np->dev = &dev->dev;
>
>         return dev;
>
> @@ -556,6 +570,10 @@ 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);
>
> +       /* Spinlock is needed for of_find_device_by_node() to work */
> +       spin_lock(&of_dev_lock);
> +       dev->of_node->dev = NULL;
> +       spin_unlock(&of_dev_lock);
>         of_node_clear_flag(dev->of_node, OF_POPULATED);
>         of_node_clear_flag(dev->of_node, OF_POPULATED_BUS);
>
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 0cf857012f11..f2b4912cbca1 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -48,6 +48,8 @@ struct property {
>  struct of_irq_controller;
>  #endif
>
> +struct device;
> +
>  struct device_node {
>         const char *name;
>         phandle phandle;
> @@ -68,6 +70,7 @@ struct device_node {
>         unsigned int unique_id;
>         struct of_irq_controller *irq_trans;
>  #endif
> +       struct device *dev;             /* Device created from this node */
>  };
>
>  #define MAX_PHANDLE_ARGS 16
> --
> 2.22.0.rc1.257.g3120a18244-goog
>