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

From: Andrew Lunn <andrew@lunn.ch> Sent: Tuesday, August 20, 2019 9:04 PM

On Tue, Aug 20, 2019 at 02:32:26AM +0000, Andy Duan wrote:

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From: Andrew Lunn <andrew@lunn.ch>

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On Mon, Aug 19, 2019 at 05:11:14PM +0000, Marco Hartmann wrote:

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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?

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Thanks
        Andrew

i.MX legacy platforms like i.MX6/7 series, they doesn't support Write & Read

Increment.

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But for i.MX8MQ/MM series, it support C45 full features like Write & Read

Increment.

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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

It still trigger an interrupt to wakeup the completion, we have to wait FEC_MII_TIMEOUT.
Older chips just support part of C45 feature just like the patch implementation.