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Message-ID: <2766c2b3-3262-78f5-d736-990aaa385eeb@pobox.com>
Date: Fri, 14 Jun 2019 17:53:02 -0500
From: Daniel Santos <daniel.santos@...ox.com>
To: Daniel Golle <daniel@...rotopia.org>, Felix Fietkau <nbd@....name>,
openwrt-devel <openwrt-devel@...ts.openwrt.org>,
John Crispin <blogic@...nwrt.org>,
Michael Lee <igvtee@...il.com>, netdev@...r.kernel.org
Subject: Understanding Ethernet Architecture (I/O --> MDIO --> MII vs I/O -->
MAC) for mt7620 (OpenWRT)
Hello,
I'm still fairly new to Ethernet drivers and there are a lot of
interesting pieces. What I need help with is understanding MDIO -->
(R)MII vs direct I/O to the MAC (e.g., via ioread32, iowrite32). Why is
there not always a struct mii_bus to talk to this hardware? Is it
because the PHY and/or MAC hardware sometimes attached via an MDIO
device and sometimes directly to the I/O bus? Or does some type of
"indirect access" need to be enabled for that to work?
I might be trying to do something that's unnecessary however, I'm not
sure yet. I need to add functionality to change a port's
auto-negotiate, duplex, etc. I'm adding it to the swconfig first and
then will look at adding it for DSA afterwards. When I run "swconfig
dev switch0 port 0 show", the current mt7530 / mt7620 driver is querying
the MAC status register (at base + 0x3008 + 0x100 * port, described on
pages 323-324 of the MT7620 Programming Guide), so I implemented the
"set" functionality by modifying the MAC's control register (offset
0x3000 on page 321), but it doesn't seem to change anything. So I
figured maybe I need to modify the MII interface's control register for
the port (page 350), but upon debugging I can see that the struct
mii_bus *bus member is NULL.
So should I be able to change it via the MAC's control register and
something else is wrong? Why is there no struct mii_bus? Can I talk to
the MII hardware in some other way?
Thanks,
Daniel
https://download.villagetelco.org/hardware/MT7620/MT7620_ProgrammingGuide.pdf
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