Date:	Thu, 5 Sep 2013 11:11:47 +0200
From:	Willy Tarreau <w@....eu>
To:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Cc:	Ethan Tuttle <ethan@...antuttle.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Lior Amsalem <alior@...vell.com>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	Jochen De Smet <jochen.armkernel@...hnim.org>,
	Peter Sanford <psanford@...rbuy.io>,
	Chény Yves-Gael <yves@...ny.fr>,
	Ryan Press <ryan@...sslab.us>,
	Simon Guinot <simon.guinot@...uanux.org>, vdonnefort@...ie.com,
	stable@...r.kernel.org, Jason Cooper <jason@...edaemon.net>
Subject: Re: [PATCH] net: mvneta: properly disable HW PHY polling and ensure adjust_link() works

On Thu, Sep 05, 2013 at 10:26:59AM +0200, Thomas Petazzoni wrote:
> > One simpler solution for them could be to slightly modify the boot loader
> > so that it sets the MAC address on the two ethernet controllers prior to
> > boot. Then your code which checks if a MAC is already set will simply
> > work.
> 
> This works when the network driver is compiled 'statically' inside the
> kernel. When compiled as a module, then the gatable clock of the
> network interface will be gated at the end of the kernel boot, before
> the mvneta module is probe. And gating the network interface clocks
> means that it will loose its state, including its MAC address. So it's
> not an entirely perfect solution either, but I admit that on such
> platforms, the network driver is most likely compiled statically, so it
> would probably suit the needs of most people.

Agreed.

> Note that this can be done without doing any change in the bootloader.
> For example, on a Mirabox, you can do:
> 
>    mw.l 0xD0072414 0x5C93; mw.l 0xD0072418 0xF0AD4E01; mw.l 0xD0076414 0x5C94; mw.l 0xD0076418 0xF0AD4E01; bootm
> 
> to boot your kernel. This will program the MAC addresses for both
> network interfaces in the network controllers, so that when booting
> Linux, you get:
> 
> [   42.122881] mvneta d0070000.ethernet eth0: Using hardware mac address f0:ad:4e:01:5c:93
> [   42.385398] mvneta d0074000.ethernet eth1: Using hardware mac address f0:ad:4e:01:5c:94
> 
> You add that to your default U-Boot boot script, and that's it, you
> have stable MAC addresses.

Hmmm that's quite interesting. Unfortunately I don't see an easy way to
make this directly rely on the ethaddr/eth1addr so that end users can
simply cut-n-paste a few lines into the u-boot config. But anyway that
can be useful.

> > A last one would be to have the mvneta module accept an array of addresses
> > as a module parameter. This way it would just require a minor change in the
> > kernel's cmdline to pass the MAC addresses. I remember seeing this in the
> > past, I don't remember the platform (maybe the NSLU2 but I could be wrong).
> 
> The situation of module parameters to pass MAC addresses was a bit
> fuzzy. There was once a proposal to add a generic kernel parameter to
> do this, but it was rejected by David Miller (I believe not on specific
> implementation details, but on the general idea). However, there are
> numerous drivers in the tree that do provide a custom module parameter
> to set MAC addresses.

Yes, I remember using this with the sunhme driver many years ago when
we did not have access to the onboard rom to retrieve the MAC address.

> However, with the above suggestion of U-Boot scripting, I believe we
> have a relatively easy solution for people to use.

We could provide a script to do it more conveniently for the user :-)

Best regards,
Willy

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