netdev - Re: [PATCH net v1] net: dsa: mv88e6xxx: Make unsupported C45 reads return 0xffff

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Message-ID: <20240122125202.yfyxz2flwpum3v22@skbuf>
Date: Mon, 22 Jan 2024 14:52:02 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: Andrew Lunn <andrew@...n.ch>
Cc: netdev-maintainers <edumazet@...gle.com>, kuba@...nel.org,
	pabeni@...hat.com, davem@...emloft.net,
	netdev <netdev@...r.kernel.org>, stable@...r.kernel.org,
	Tim Menninger <tmenninger@...estorage.com>
Subject: Re: [PATCH net v1] net: dsa: mv88e6xxx: Make unsupported C45 reads
 return 0xffff

On Mon, Jan 22, 2024 at 02:29:21PM +0200, Vladimir Oltean wrote:
> On Mon, Jan 22, 2024 at 02:24:57PM +0200, Vladimir Oltean wrote:
> > > Fixes: 1a136ca2e089 ("net: mdio: scan bus based on bus capabilities for C22 and C45")
> > > Fixes: da099a7fb13d ("net: phy: Remove probe_capabilities")
> 
> Also: commit da099a7fb13d ("net: phy: Remove probe_capabilities") is not
> a functional change, so I don't see why it should be blamed? I suppose
> 'git bisect' would find 1a136ca2e089 ("net: mdio: scan bus based on bus
> capabilities for C22 and C45")?

One reason why this patch is not better than Tim's is because it does
not tell phylib straight away that there are no C45 capabilities on the
bus. It lets phylib scan the bus for all addresses, which yes, is not as
slow because no actual MDIO access is performed, but is also not as fast
as simply omitting the c45 ops altogether. I think it would be good to
state what would there be to lose if we just went for Tim's approach.