linux-kernel - Re: [PATCH] drivers/soc/tegra: Replace dev

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Message-Id: <D0TBBT7FZ3E0.14ZFOT5S4QZPR@gmail.com>
Date: Thu, 25 Apr 2024 17:35:46 +0200
From: "Thierry Reding" <thierry.reding@...il.com>
To: "Miguel Miranda" <mmikernel@...il.com>, <jonathanh@...dia.com>,
 <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Cc: <skhan@...uxfoundation.org>, <javier.carrasco.cruz@...il.com>,
 <julia.lawall@...ia.fr>
Subject: Re: [PATCH] drivers/soc/tegra: Replace dev_node refcount management

On Wed Apr 24, 2024 at 3:53 AM CEST, Miguel Miranda wrote:
> Remove the manual refcount management of device_node
> and instead, use scope-based resource management.
>
> While the pointer never gets out of scope it reduces
> somehow the risk of missing the of_node_put() call.

I don't understand what you're trying to say here.

> Suggested-by: Julia Lawall <julia.lawall@...ia.fr>
> Signed-off-by: Miguel Miranda <mmikernel@...il.com>
> ---
> I only have a deprecated jetson nano dev-kit, but need
> to test this on hardware. I am exploring options to
> build a rootfs to test this using qemu-system-aarch64.

It doesn't look like it'll be necessary to extensively test this. Just
by inspecting this we can see that it doesn't change behaviour. There
isn't really a big advantage to employ the __free() mechanism here since
we have exactly one of_node_put() to clean up, but I guess why not. So
maybe reword that commit message to be less confusing.

Thierry

> ---
>  drivers/soc/tegra/common.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/drivers/soc/tegra/common.c b/drivers/soc/tegra/common.c
> index dff6d5ef4e46..94d11102d90f 100644
> --- a/drivers/soc/tegra/common.c
> +++ b/drivers/soc/tegra/common.c
> @@ -28,14 +28,12 @@ static const struct of_device_id tegra_machine_match[] = {
>  bool soc_is_tegra(void)
>  {
>  	const struct of_device_id *match;
> -	struct device_node *root;
> +	struct device_node *root __free(device_node) = of_find_node_by_path("/");
>  
> -	root = of_find_node_by_path("/");
>  	if (!root)
>  		return false;
>  
>  	match = of_match_node(tegra_machine_match, root);
> -	of_node_put(root);
>  
>  	return match != NULL;
>  }


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