linux-kernel - Re: [EXT] Re: [PATCH net-next 0/1] net: fec: add C45 MDIO read/write support

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Message-ID: <20190820130403.GH29991@lunn.ch>
Date:   Tue, 20 Aug 2019 15:04:03 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Andy Duan <fugang.duan@....com>
Cc:     Marco Hartmann <marco.hartmann@....com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Christian Herber <christian.herber@....com>
Subject: Re: [EXT] Re: [PATCH net-next 0/1] net: fec: add C45 MDIO read/write
 support

On Tue, Aug 20, 2019 at 02:32:26AM +0000, Andy Duan wrote:
> From: Andrew Lunn <andrew@...n.ch>
> > On Mon, Aug 19, 2019 at 05:11:14PM +0000, Marco Hartmann wrote:
> > > As of yet, the Fast Ethernet Controller (FEC) driver only supports
> > > Clause 22 conform MDIO transactions. IEEE 802.3ae Clause 45 defines a
> > > modified MDIO protocol that uses a two staged access model in order to
> > > increase the address space.
> > >
> > > This patch adds support for Clause 45 conform MDIO read and write
> > > operations to the FEC driver.
> > 
> > Hi Marco
> > 
> > Do all versions of the FEC hardware support C45? Or do we need to make use
> > of the quirk support in this driver to just enable it for some revisions of FEC?
> > 
> > Thanks
> >         Andrew
> 
> i.MX legacy platforms like i.MX6/7 series, they doesn't support Write & Read Increment.
> But for i.MX8MQ/MM series, it support C45 full features like Write & Read Increment.
> 
> For the patch itself, it doesn't support Write & Read Increment, so I think the patch doesn't
> need to add quirk support.

Hi Andy

So what happens with something older than a i.MX8MQ/MM when a C45
transfer is attempted? This patch adds a new write. Does that write
immediately trigger a completion interrupt? Does it never trigger an
interrupt, and we have to wait FEC_MII_TIMEOUT?

Ideally, if the hardware does not support C45, we want it to return
EOPNOTSUPP.

Thanks
	Andrew