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Date: Fri, 9 Jan 2026 08:31:30 -0800
From: Jakub Kicinski <kuba@kernel.org>
To: "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc: Heiner Kallweit <hkallweit1@gmail.com>, Andrew Lunn <andrew@lunn.ch>,
 Andrew Lunn <andrew+netdev@lunn.ch>, Paolo Abeni <pabeni@redhat.com>, Eric
 Dumazet <edumazet@google.com>, David Miller <davem@davemloft.net>,
 "netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: [PATCH net-next] net: phy: fixed_phy: replace list of fixed
 PHYs with static array
Message-ID: <20260109083130.50ae4ba9@kernel.org>
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References: <e14f6119-9bf9-4e9d-8e14-a8cb884cbd5c@gmail.com>
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On Fri, 9 Jan 2026 15:10:18 +0000 Russell King (Oracle) wrote:
> > 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.

True, if there's no existing locking wrap it in a do {} while and use
test_and_set_bit() as the condition for repeat.