linux-kernel - Re: [PATCH v2 03/16] ACPI: property: Rework acpi_graph_get_next

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Message-ID: <20250924093934.GC28073@pendragon.ideasonboard.com>
Date: Wed, 24 Sep 2025 12:39:34 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-input@...r.kernel.org, linux-leds@...r.kernel.org,
	linux-media@...r.kernel.org, netdev@...r.kernel.org,
	linux-spi@...r.kernel.org, "Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Daniel Scally <djrscally@...il.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Javier Carrasco <javier.carrasco@...fvision.net>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Lee Jones <lee@...nel.org>, Pavel Machek <pavel@...nel.org>,
	Matthias Fend <matthias.fend@...end.at>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Paul Elder <paul.elder@...asonboard.com>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Horatiu Vultur <horatiu.vultur@...rochip.com>,
	UNGLinuxDriver@...rochip.com, Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Mark Brown <broonie@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v2 03/16] ACPI: property: Rework
 acpi_graph_get_next_endpoint()

Hi Sakari,

On Wed, Sep 24, 2025 at 10:45:49AM +0300, Sakari Ailus wrote:
> Rework the code obtaining the next endpoint in
> acpi_graph_get_next_endpoint(). The resulting code removes unnecessary
> contitionals and should be easier to follow.
> 
> Suggested-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Signed-off-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> ---
>  drivers/acpi/property.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
> index 3e85900080ac..5438592dc136 100644
> --- a/drivers/acpi/property.c
> +++ b/drivers/acpi/property.c
> @@ -1399,14 +1399,15 @@ static struct fwnode_handle *acpi_graph_get_next_endpoint(
>  	if (!port)
>  		return NULL;
>  
> -	endpoint = acpi_get_next_subnode(port, prev);
> -	while (!endpoint) {
> -		port = acpi_get_next_subnode(fwnode, port);
> -		if (!port)
> +	do {
> +		endpoint = acpi_get_next_subnode(port, prev);
> +		if (endpoint)
>  			break;
> +
> +		port = acpi_get_next_subnode(fwnode, port);
>  		if (is_acpi_graph_node(port, "port"))
> -			endpoint = acpi_get_next_subnode(port, NULL);
> -	}
> +			prev = NULL;

Isn't there an issue here ? If the next subnode of fwnode is not a port,
the next iteration of the do loop will attempt to get an endpoint from
that non-port node. Maybe the acpi_get_next_subnode() that will try to
get the endpoint from the non-port port will return NULL because prev
won't be a child of port, but that seems fragile.

I think the following would be easier to understand:

	do {
		endpoint = acpi_get_next_subnode(port, prev);
		if (endpoint)
			break;

		prev = NULL;

		do {
			port = acpi_get_next_subnode(fwnode, port);
		} while (port && !is_acpi_graph_node(port, "port"));
	} while (port);

> +	} while (port);
>  
>  	/*
>  	 * The names of the endpoint nodes begin with "endpoint@" followed by
> 

-- 
Regards,

Laurent Pinchart