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

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Message-ID: <aWEaWvV_0SfylwW5@shell.armlinux.org.uk>
Date: Fri, 9 Jan 2026 15:10:18 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Heiner Kallweit <hkallweit1@...il.com>, Andrew Lunn <andrew@...n.ch>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	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 Thu, Jan 08, 2026 at 06:11:02PM -0800, 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.
> 
> 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);

Racy without locking.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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