Hi Sarvana,
I'm not reviewing patches 1-5 in any detail, given my reply to patch 0.
But I had already skimmed through this patch before I received the
email for patch 0, so I want to make one generic comment below,
to give some feedback as you continue thinking through possible
implementations to solve the underlying problems.
On 5/23/19 6:01 PM, Saravana Kannan 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@xxxxxxxxxx>
> ---
> 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 */
We have actively been working on shrinking the size of struct device_node,
as part of reducing the devicetree memory usage. As such, we need strong
justification for adding anything to this struct. For example, proof that
there is a performance problem that can only be solved by increasing the
memory usage.
-Frank
> };
>
> #define MAX_PHANDLE_ARGS 16
>
