netdev - Re: [PATCH net-next 1/1] net: dsa: qca8k: Fix internal PHY MDIO address

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Date:   Thu, 21 Mar 2019 23:24:13 +0100
From:   Christian Lamparter <chunkeey@...il.com>
To:     Marek Behun <marek.behun@....cz>
Cc:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org,
        Andrew Lunn <andrew@...n.ch>,
        Michal Vokáč <vokac.m@...il.com>,
        John Crispin <john@...ozen.org>,
        Wei Yongjun <weiyongjun1@...wei.com>
Subject: Re: [PATCH net-next 1/1] net: dsa: qca8k: Fix internal PHY MDIO address

(Bottom post?)
On Thursday, March 21, 2019 8:55:55 PM CET Marek Behun wrote:
> Hi,
> 
> Oh, I didn't know about Christian's patch.
> 
> I shall test on our device tomorrow. If it works, we will use internal
> PHY access.
> 
> But I think that qca8k_port_to_phy should be used in the external mode
> as well. On our device the PHYs are mapped on 0-4 on the master bus even
> in that mode.

Hm, it's not really a "external mode". But let's try one more time. The
idea is that if an external mdio-bus (from the SoC) has already registered
the PHY 0x0 - 0x4 from the QCA8337, the qca8k should not expose the same
PHYs as it's own mdio-bus because then the PHYs end up being registered twice.

If you look at the mdio-bus communications during boot you can definitly see
the funkyness: every PHY gets initialized twice. You can also see this
"duplication" in /sys/class/mdio_bus. In this directory you'll have a mdio-bus
from the SoC and another one dsa-0:0 from the qca8k. If you look into those
you'll notice that their both the same.

As for why this happend. I think I found the culprit in a "missed"
requirement from one of Andrew Lunn's reponses to the initial qca8k patch:
<https://lore.kernel.org/patchwork/patch/715974/#902734>

In this post, he described the Device-Tree dts configuration we use today.
But at the end he requests: 
"and remove the phy_read() and phy_write() functions."

But from what I can tell, this important bit of information was lost
during the night. Because they show up in v2+:
https://lore.kernel.org/patchwork/patch/716989/

(So I guess I have to add Fixes: to my patch as well)

Cheers,
Christian