Subject: Re: [PATCH 6/6] net: mvpp2: use device_for_each_child_node() to access device child nodes

From: "Russell King (Oracle)" <[email-masked]>
Date: Mon, 29 Jul 2024 09:23:28 +0100

On Sat, Jul 06, 2024 at 05:23:38PM +0200, Javier Carrasco wrote:
> The iterated nodes are direct children of the device node, and the
> `device_for_each_child_node()` macro accounts for child node
> availability.
> 
> `fwnode_for_each_available_child_node()` is meant to access the child
> nodes of an fwnode, and therefore not direct child nodes of the device
> node.
> 
> The child nodes within mvpp2_probe are not accessed outside the lopps,

"lopps" ?

> and the socped version of the macro can be used to automatically

"socped" ?

> decrement the refcount on early exits.
> 
> Use `device_for_each_child_node()` and its scoped variant to indicate
> device's direct child nodes.
> 
> Signed-off-by: Javier Carrasco <[email-masked]>
> ---
>  drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 13 ++++---------
>  1 file changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> index 9adf4301c9b1..97f1faab6f28 100644
> --- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> +++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> @@ -7417,8 +7417,6 @@ static int mvpp2_get_sram(struct platform_device *pdev,
>  
>  static int mvpp2_probe(struct platform_device *pdev)
>  {
> -	struct fwnode_handle *fwnode = pdev->dev.fwnode;
> -	struct fwnode_handle *port_fwnode;
>  	struct mvpp2 *priv;
>  	struct resource *res;
>  	void __iomem *base;
> @@ -7591,7 +7589,7 @@ static int mvpp2_probe(struct platform_device *pdev)
>  	}
>  
>  	/* Map DTS-active ports. Should be done before FIFO mvpp2_init */
> -	fwnode_for_each_available_child_node(fwnode, port_fwnode) {
> +	device_for_each_child_node_scoped(&pdev->dev, port_fwnode) {
>  		if (!fwnode_property_read_u32(port_fwnode, "port-id", &i))
>  			priv->port_map |= BIT(i);
>  	}
> @@ -7614,7 +7612,7 @@ static int mvpp2_probe(struct platform_device *pdev)
>  		goto err_axi_clk;
>  
>  	/* Initialize ports */
> -	fwnode_for_each_available_child_node(fwnode, port_fwnode) {
> +	device_for_each_child_node_scoped(&pdev->dev, port_fwnode) {
>  		err = mvpp2_port_probe(pdev, port_fwnode, priv);
>  		if (err < 0)
>  			goto err_port_probe;
> @@ -7653,10 +7651,8 @@ static int mvpp2_probe(struct platform_device *pdev)
>  	return 0;
>  
>  err_port_probe:
> -	fwnode_handle_put(port_fwnode);
> -
>  	i = 0;
> -	fwnode_for_each_available_child_node(fwnode, port_fwnode) {
> +	device_for_each_child_node_scoped(&pdev->dev, port_fwnode) {
>  		if (priv->port_list[i])
>  			mvpp2_port_remove(priv->port_list[i]);
>  		i++;
> @@ -7677,13 +7673,12 @@ static int mvpp2_probe(struct platform_device *pdev)
>  static void mvpp2_remove(struct platform_device *pdev)
>  {
>  	struct mvpp2 *priv = platform_get_drvdata(pdev);
> -	struct fwnode_handle *fwnode = pdev->dev.fwnode;
>  	int i = 0, poolnum = MVPP2_BM_POOLS_NUM;
>  	struct fwnode_handle *port_fwnode;
>  
>  	mvpp2_dbgfs_cleanup(priv);
>  
> -	fwnode_for_each_available_child_node(fwnode, port_fwnode) {
> +	device_for_each_child_node(&pdev->dev, port_fwnode) {
>  		if (priv->port_list[i]) {
>  			mutex_destroy(&priv->port_list[i]->gather_stats_lock);
>  			mvpp2_port_remove(priv->port_list[i]);

This loop is just silly. There is no need to iterate the child nodes.
port_fwnode is not used, and the loop boils down to:

	for (i = 0; i < priv->port_count; i++) {
		mutex_destroy(&priv->port_list[i]->gather_stats_lock);
		mvpp2_port_remove(priv->port_list[i]);
	}

Not only is walking the child nodes not necessary, but checking whether
the pointer is NULL is also unnecessary. mvpp2_port_probe() populates
the array using:

        priv->port_list[priv->port_count++] = port;

and "port" can not be NULL here, so we're guaranteed that all port_list
entries for 0..priv->port_count will be non-NULL, and the driver makes
this assumption in multiple places.

In fact, I'd say that using fwnode_for_each_available_child_node() or
device_for_each_child_node() is buggy here if the availability of the
children change - it could leave ports not cleaned up.

-- 
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