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

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Date:   Wed, 3 Nov 2021 20:36:49 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Grygorii Strashko <grygorii.strashko@...com>
Cc:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        "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()

On Wed, Nov 03, 2021 at 08:42:07PM +0200, Grygorii Strashko wrote:
> 
> 
> On 03/11/2021 02:27, Andrew Lunn wrote:
> > > > What i find interesting is that you and the other resent requester are
> > > > using the same user space tool. If you implement C45 over C22 in that
> > > > tool, you get your solution, and it will work for older kernels as
> > > > well. Also, given the diverse implementations of this IOTCL, it
> > > > probably works for more drivers than just those using phy_mii_ioctl().
> > > 
> > > Do you mean change uapi, like
> > >   add mdio_phy_id_is_c45_over_c22() and
> > >   flag #define MDIO_PHY_ID_C45_OVER_C22 0x4000?
> > 
> > No, i mean user space implements C45 over C22. Make phytool write
> > MII_MMD_CTRL and MII_MMD_DATA to perform a C45 over C22.
> 
> Now I give up - as mentioned there is now way to sync User space vs Kernel
> MMD transactions and so no way to get trusted results.

Except that it will probably work 99% of the time, which is enough for
a debug tool. phylib is pretty idle most of the time, it just polls
the PHY once a second to see if the link status has changed. And does
not poll at all if interrupts are wired up. And you can always do a
read three times and see if you get the same answer, or do a write
followed by a read to see if the write actually happened correctly, or
corrupted some other register.

	Andrew