netdev - Re: [RFC PATCH] net: phy/mdio: enable mmd indirect access through phy_mii

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Date:   Tue, 2 Nov 2021 01:49:42 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Grygorii Strashko <grygorii.strashko@...com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        linux-kernel@...r.kernel.org, Vignesh Raghavendra <vigneshr@...com>
Subject: Re: [RFC PATCH] net: phy/mdio: enable mmd indirect access through
 phy_mii_ioctl()

> The use of the indirect registers is specific to PHYs, and we already
> know that various PHYs don't support indirect access, and some emulate
> access to the EEE registers - both of which are handled at the PHY
> driver level.

That is actually an interesting point. Should the ioctl call actually
use the PHY driver read_mmd and write_mmd? Or should it go direct to
the bus? realtek uses MII_MMD_DATA for something to do with suspend,
and hence it uses genphy_write_mmd_unsupported(), or it has its own
function emulating MMD operations.

So maybe the ioctl handler actually needs to use __phy_read_mmd() if
there is a phy at the address, rather than go direct to the bus?

Or maybe we should just say no, you should do this all from userspace,
by implementing C45 over C22 in userspace, the ioctl allows that, the
kernel does not need to be involved.

	Andrew