linux-kernel - Re: [net-next PATCH v12 07/13] net: mdio: regmap: add support for multiple valid addr

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Message-ID: <Z9SZRDykbTwvGW6S@shell.armlinux.org.uk>
Date: Fri, 14 Mar 2025 21:01:56 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>
Cc: Christian Marangi <ansuelsmth@...il.com>, Lee Jones <lee@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Vladimir Oltean <olteanv@...il.com>,
	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, netdev@...r.kernel.org,
	upstream@...oha.com
Subject: Re: [net-next PATCH v12 07/13] net: mdio: regmap: add support for
 multiple valid addr

On Fri, Mar 14, 2025 at 08:41:33PM +0100, Andrew Lunn wrote:
> On Sun, Mar 09, 2025 at 06:45:43PM +0100, Christian Marangi wrote:
> > On Sun, Mar 09, 2025 at 05:36:49PM +0000, Russell King (Oracle) wrote:
> > > On Sun, Mar 09, 2025 at 06:26:52PM +0100, Christian Marangi wrote:
> > > > +/* If a non empty valid_addr_mask is passed, PHY address and
> > > > + * read/write register are encoded in the regmap register
> > > > + * by placing the register in the first 16 bits and the PHY address
> > > > + * right after.
> > > > + */
> > > > +#define MDIO_REGMAP_PHY_ADDR		GENMASK(20, 16)
> > > > +#define MDIO_REGMAP_PHY_REG		GENMASK(15, 0)
> > > 
> > > Clause 45 PHYs have 5 bits of PHY address, then 5 bits of mmd address,
> > > and then 16 bits of register address - significant in that order. Can
> > > we adjust the mask for the PHY address later to add the MMD between
> > > the PHY address and register number?
> > >
> > 
> > Honestly to future proof this, I think a good idea might be to add
> > helper to encode these info and use Clause 45 format even for C22.
> > Maybe we can use an extra bit to signal if the format is C22 or C45.
> > 
> > BIT(26) 0: C22 1:C45
> > GENMASK(25, 21) PHY ADDR
> > GENMASK(20, 16) MMD ADDR
> > GENMASK(15, 0) REG
> 
> If you look back at older kernels, there was some helpers to do
> something like this, but the C22/C45 was in bit 31. When i cleaned up
> MDIO drivers to have separate C22 and C45 read/write functions, they
> become redundant and they were removed. You might want to bring them
> back again.

I'd prefer we didn't bring that abomination back. The detail about how
things are stored in regmap should be internal within regmap, and I
think it would be better to have an API presented that takes sensible
parameters, rather than something that's been encoded.

-- 
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