linux-kernel - Re: [PATCH v2] driver core: auxiliary bus: Optimize logic of auxiliary_match

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Message-Id: <DCJ52UB7OIXR.3MS54RJKMI4OK@kernel.org>
Date: Wed, 03 Sep 2025 13:46:58 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Zijun Hu" <zijun_hu@...oud.com>
Cc: "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>, "Dave Ertman"
 <david.m.ertman@...el.com>, "Ira Weiny" <ira.weiny@...el.com>, "Leon
 Romanovsky" <leon@...nel.org>, "Rafael J. Wysocki" <rafael@...nel.org>,
 <linux-kernel@...r.kernel.org>, "Zijun Hu" <zijun.hu@....qualcomm.com>
Subject: Re: [PATCH v2] driver core: auxiliary bus: Optimize logic of
 auxiliary_match_id()

On Wed Sep 3, 2025 at 1:37 PM CEST, Zijun Hu wrote:
> diff --git a/drivers/base/auxiliary.c b/drivers/base/auxiliary.c
> index 12ffdd8437567f282374bbf3775d9de7ca0dc4c7..ed2537cf3b048149e784e5a582631db549050734 100644
> --- a/drivers/base/auxiliary.c
> +++ b/drivers/base/auxiliary.c
> @@ -171,17 +171,18 @@
>  static const struct auxiliary_device_id *auxiliary_match_id(const struct auxiliary_device_id *id,
>  							    const struct auxiliary_device *auxdev)
>  {
> -	for (; id->name[0]; id++) {
> -		const char *p = strrchr(dev_name(&auxdev->dev), '.');
> -		int match_size;
> +	const char *auxdev_name = dev_name(&auxdev->dev);

I feel like this is a bit too ambitious. Using dev_name() directly for the calls
below seems more obvious to me.

Yes, dev_name() contains a branch, but I'm pretty sure the compiler optimizes
them away for subsequent calls anyways.

> +	const char *p = strrchr(auxdev_name, '.');
> +	int match_size;
>  
> -		if (!p)
> -			continue;
> -		match_size = p - dev_name(&auxdev->dev);
> +	if (!p)
> +		return NULL;
> +	match_size = p - auxdev_name;
>  
> +	for (; id->name[0]; id++) {
>  		/* use dev_name(&auxdev->dev) prefix before last '.' char to match to */
>  		if (strlen(id->name) == match_size &&
> -		    !strncmp(dev_name(&auxdev->dev), id->name, match_size))
> +		    !strncmp(auxdev_name, id->name, match_size))
>  			return id;
>  	}
>  	return NULL;
>
> ---
> base-commit: 1b237f190eb3d36f52dffe07a40b5eb210280e00
> change-id: 20250902-fix_auxbus-76bec91376db
>
> Best regards,
> -- 
> Zijun Hu <zijun.hu@....qualcomm.com>