linux-kernel - Re: [PATCH v3 2/2] dell-laptop: Expose auxiliary MAC address if available

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Date:	Fri, 20 May 2016 16:27:42 +0200
From:	Pali Rohár <pali.rohar@...il.com>
To:	Mario_Limonciello@...l.com
Cc:	kernel@...pniu.pl, mjg59@...f.ucam.org, dvhart@...radead.org,
	linux-kernel@...r.kernel.org, platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH v3 2/2] dell-laptop: Expose auxiliary MAC address if
 available

On Thursday 12 May 2016 19:08:30 Mario_Limonciello@...l.com wrote:
> > > We do mirror the information in ACPI under the system bus:
> > >
> > >     Scope (_SB)
> > >     {
> > >         Name (AMAC, Buffer (0x17)
> > >         {
> > >             "_AUXMAC_#847BEB5992D2#"
> > >         })
> > >     }
> > >
> > > I don't know how to properly access this from the kernel side.  I noticed
> > that most drivers that reference ACPI nodes refer to devices, not something
> > hanging off the system bus.
> > > If you could advise the right way to go about that, I would appreciate it.
> > 
> > So there are two ways how to read that MAC address. One is via SMM and
> > one via ACPI.
> 
> Yes, this isn't a general statement for read only static information, but in this case it is true.
> 
> > You can also read ACPI buffer (name is probably \_SB.AMAC) with ACPI
> > functions in kernel. Ask ACPI people, for correct API. I'm sure this is possible
> > also without creating new ACPI driver...
> 
> Thanks will do.

I think that acpi_get_handle() and acpi_evaluate_object() methods are
those which you want to use.

> > > If I can access that, maybe it's better to do this directly as a patch to the
> > Ethernet driver in question (r8152).
> > > That's actually how it's handled on the OS side for Windows too from what I
> > understand.
> > > We have some FW bit set in them to indicate they're Dell Realtek products
> > (don't have this detail yet).
> > > When they see that bit they look for that ACPI buffer and use it to set the
> > MAC address the OS sees.
> > 
> > Maybe it should be better to chose same way as Windows drivers? Better
> > ask on netdev mailing list and ping maintainers of that ethernet driver what
> > they think about it.
> > 
> > For me it sounds like a better solution (patching that ethernet driver) as
> > exporting some non-standard sysfs node from kernel with MAC address and
> > then using another tool which send that MAC address back to kernel.
> > 
> 
> Great, thank you for your feedback.  I'll wander down that rabbit hole.

Ok, CC me next discussion.

-- 
Pali Rohár
pali.rohar@...il.com