linux-kernel - Re: [net-next,PATCH 1/2] net: dsa: microchip: Add emulated MIIM access to switch LED config registers

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Message-ID: <ec7861e2-85f5-45bf-bff6-19bc5009cac2@lunn.ch>
Date: Thu, 16 Jan 2025 14:06:07 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Marek Vasut <marex@...x.de>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Russell King <linux@...linux.org.uk>,
	Tristram Ha <tristram.ha@...rochip.com>,
	UNGLinuxDriver@...rochip.com, Vladimir Oltean <olteanv@...il.com>,
	Woojung Huh <woojung.huh@...rochip.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [net-next,PATCH 1/2] net: dsa: microchip: Add emulated MIIM
 access to switch LED config registers

> This preparatory patch exposes the LED control bits in those Switch Config
> Registers by mapping them at high addresses in the MIIM space, so the PHY
> driver can access those registers and surely not collide with the existing
> MIIM block registers. The two registers which are exposed are the global
> Register 11 (0x0B): Global Control 9 as MIIM block register 0x0b00 and
> port specific Register 29/45/61 (0x1D/0x2D/0x3D): Port 1/2/3 Control 10
> as MIIM block register 0x0d00 . The access to those registers is further
> restricted only to the LED configuration bits to prevent the PHY driver
> or userspace tools like 'phytool' from tampering with any other switch
> configuration through this interface.

I do wounder about using register numbers outside of the 0-31
range. We never have enforced it, but these clearly break 802.3 C22.

I wounder if it would be better to emulate pages as well. The PHY
driver already has lanphy_write_page_reg() and
lanphy_read_page_reg(). Could you emulate what those need?  It adds a
lot of complexity, but it should be future proof.

What might be simpler is to expose an emulated C45 register range, and
put the registers in the vendor section.


	Andrew