linux-kernel - Re: [net-next PATCH v14 07/16] net: mdio: regmap: add support for C45 read/write

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Message-ID: <5472c608-df78-4433-a086-6ac9323d9d35@lunn.ch>
Date: Thu, 10 Apr 2025 22:56:32 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Christian Marangi <ansuelsmth@...il.com>
Cc: 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>,
	Russell King <linux@...linux.org.uk>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	"Chester A. Unal" <chester.a.unal@...nc9.com>,
	Daniel Golle <daniel@...rotopia.org>,
	DENG Qingfang <dqfext@...il.com>,
	Sean Wang <sean.wang@...iatek.com>, Simon Horman <horms@...nel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-mediatek@...ts.infradead.org, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	upstream@...oha.com
Subject: Re: [net-next PATCH v14 07/16] net: mdio: regmap: add support for
 C45 read/write

> Hope you can give some guidance about this! Happy to split this once we
> find a common point on how to proceed with this.

One thing i'm failing to understand is, why use a regmap at all. For a
single C22 device it make sense. 32 linear registers, nice and
simple. They could be memory mapped, I2C addresses, SPI addresses,
etc. The regmap implementer probably just adds a constant offset and
does a hardware access.

Multiple C22 devices gets us into a two dimensional problem. Multiple
C45 devices gives us a three dimensional problem. Mixing multiple C22
and C45 gets us a four dimensional problem. This is a long way from
regmaps nice simple model of linear registers.

What does regmap bring here?

	Andrew