linux-kernel - Re: [PATCH next] arch: powerpc: platforms: Remove unnecessary call to of_node

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Message-ID: <87h6eo3h4i.fsf@mail.lhotse>
Date: Thu, 23 May 2024 21:25:01 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Prabhav Kumar Vaish <pvkumar5749404@...il.com>, akpm@...ux-foundation.org
Cc: npiggin@...il.com, christophe.leroy@...roup.eu,
 naveen.n.rao@...ux.ibm.com, linuxppc-dev@...ts.ozlabs.org,
 linux-kernel@...r.kernel.org, skhan@...uxfoundation.org,
 julia.lawall@...ia.fr, javier.carrasco.cruz@...il.com, Prabhav Kumar Vaish
 <pvkumar5749404@...il.com>
Subject: Re: [PATCH next] arch: powerpc: platforms: Remove unnecessary call
 to of_node_get

Prabhav Kumar Vaish <pvkumar5749404@...il.com> writes:
> `dev->of_node` has a pointer to device node, of_node_get call seems
> unnecessary.

Sorry but it is necessary.

> Signed-off-by: Prabhav Kumar Vaish <pvkumar5749404@...il.com>
> ---
>  arch/powerpc/platforms/cell/iommu.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/platforms/cell/iommu.c b/arch/powerpc/platforms/cell/iommu.c
> index 4cd9c0de22c2..5b794ce08689 100644
> --- a/arch/powerpc/platforms/cell/iommu.c
> +++ b/arch/powerpc/platforms/cell/iommu.c
> @@ -780,14 +780,13 @@ static int __init cell_iommu_init_disabled(void)
>  static u64 cell_iommu_get_fixed_address(struct device *dev)
>  {
>  	u64 cpu_addr, size, best_size, dev_addr = OF_BAD_ADDR;
> -	struct device_node *np;
> +	struct device_node *np = dev->of_node;
>  	const u32 *ranges = NULL;
>  	int i, len, best, naddr, nsize, pna, range_size;
>  
>  	/* We can be called for platform devices that have no of_node */
> -	np = of_node_get(dev->of_node);
>  	if (!np)
> -		goto out;
> +		return dev_addr;
>  
>  	while (1) {
>  		naddr = of_n_addr_cells(np);

		nsize = of_n_size_cells(np);
		np = of_get_next_parent(np);
		if (!np)
			break;

of_get_next_parent() drops the reference of the node passed to it (np).

So if you actually tested your patch you should see a recount underflow.

cheers