netdev - Re: [PATCH net-next] net: phy: fixed_phy: replace list of fixed PHYs with static array

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Message-ID: <20260108181102.4553d618@kernel.org>
Date: Thu, 8 Jan 2026 18:11:02 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Heiner Kallweit <hkallweit1@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>, Andrew Lunn <andrew+netdev@...n.ch>,
 Russell King - ARM Linux <linux@...linux.org.uk>, Paolo Abeni
 <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>, David Miller
 <davem@...emloft.net>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: phy: fixed_phy: replace list of fixed
 PHYs with static array

On Tue, 6 Jan 2026 17:56:26 +0100 Heiner Kallweit wrote:
> +/* The DSA loop driver may allocate 4 fixed PHY's, and 4 additional
> + * fixed PHY's for a system should be sufficient.
> + */
> +#define NUM_FP	8
> +
>  struct fixed_phy {
> -	int addr;
>  	struct phy_device *phydev;
>  	struct fixed_phy_status status;
>  	int (*link_update)(struct net_device *, struct fixed_phy_status *);
> -	struct list_head node;
>  };
>  
> +static struct fixed_phy fmb_fixed_phys[NUM_FP];
>  static struct mii_bus *fmb_mii_bus;
> -static LIST_HEAD(fmb_phys);
> +static DEFINE_IDA(phy_fixed_ida);

Isn't IDA an overkill for a range this tiny?
IDA is useful if the ID range is large and may be sparse.
Here a bitmap would suffice.

DECLARE_BITMAP(phy_fixed_ids, NUM_FP); 

id = find_first_zero_bit(phy_fixed_ids, NUM_FP);
if (id >= NUM_FP)
	return -ENOSPC;

set_bit(id, phy_fixed_ids);
...