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

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Message-ID: <1263a26d-a622-45d7-8043-262f2b92ed3b@gmail.com>
Date: Fri, 9 Jan 2026 12:00:41 +0100
From: Heiner Kallweit <hkallweit1@...il.com>
To: Jakub Kicinski <kuba@...nel.org>
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 1/9/2026 3:11 AM, Jakub Kicinski wrote:
> 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.
> 

Thanks for the suggestion! The IDA has been there forever, just the definition
has been moved now. I think switching to a bitmap is a good option.
Can we handle this as a follow-up?

> 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);
> ...