Date: Sun, 21 Apr 2002 16:04:24 -0700 (PDT) From: wpaul@FreeBSD.ORG (Bill Paul) To: semenu@FreeBSD.org (Semen A. Ustimenko) Cc: freebsd-hackers@FreeBSD.org Subject: Re: MIIBUS_MEDIAINIT method Message-ID: <20020421230424.9B4B637B400@hub.freebsd.org> In-Reply-To: <20020422020233.W611-100000@def.the.net> from "Semen A. Ustimenko" at "Apr 22, 2002 02:13:12 am"
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> Hi!
>
> I was just thinking about the purpose of this method... What is it?
>
> It used to be used by NIC drivers to add something like AUI beside MII
> provided media, correct?
It is _still_ used that way. See if_xl.c. There exists a 3c905B-Combo
card which supports a 10/100 RJ-45 port, a 10Mbps-only BNC port and
a 10Mbps only AUI port. Why did I concoct MEDIAINIT for this? Because
each device can have only one ifmedia structure. When a driver uses
miibus, the ifmedia struct is initialized by the underlying PHY driver,
and that initialization does not happen until after we leave the
MAC driver's attach routine. It's not a problem to add additional
media types to the ifmedia struct later, but we need to have the PHY
driver call back to the MAC driver to do this, which is why every
PHY driver has a call to MIIBUS_MEDIAINIT() in its attach routine.
If the parent MAC driver does not implement this method, nothing
happens. But if it does implement this method, the parent can use it
to do some extra ifmedia_add()s to tack on some extra media types.
> But it looks like every PHY's driver thinks it must call MEDIAINIT in its
> attach() routine. So, if there would be two PHY on MII (can this happen?),
Yes, though it's rare, and not always useful.
> then the method will be called twice, and some NIC drivers (tx, xl, dc,
> maybe more) will not behave well.
They work fine if the author of the MAC driver was smart enough to check
for this in his mediainit method and just return immmediately if the
auxilliary media types have already been ifmedia_add()ed. Right now,
the only card that uses this feature is the 3c905B-Combo, and its
hardware configuration does not permit the sort of edge condition
you are fretting over.
> Isn't it reasonable to stop all PHY drivers from calling MEDIAINIT, and
> call it once per miibus instance in miibus_attach() or miibus_probe()
> instead?
No. We want the PHY driver to set up its media types in the ifmedia
struct first, and then add our own after those, which means we have
to wait until the end of the PHY's attach routine, and it's newbus
that calls the attach routines, not the miibus code.
If you have a card or hardware configuration which is actually
causing the scenario you describe, then say so. Otherwise, keep
your fingers out of this code. No user-servicable parts inside.
Keep out of children. Do not look into laser optics with remaining
eye.
-Bill
--
=============================================================================
-Bill Paul (510) 749-2329 | Senior Engineer, Master of Unix-Fu
wpaul@windriver.com | Wind River Systems
=============================================================================
God was my co-pilot, until we crashed in the mountains and I had to eat him.
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