RE: [PATCH v6] r8152: Add support for setting pass through MAC address on RTL8153-AD

[<Mario_Limonciello@Dell.com>]

> -----Original Message-----
> From: Pali Rohár [mailto:pali.rohar@gmail.com]
> Sent: Tuesday, June 14, 2016 11:48 AM
> To: Greg KH <gregkh@linuxfoundation.org>
> Cc: David Miller <davem@davemloft.net>; andrew@lunn.ch; Limonciello,
> Mario <Mario_Limonciello@Dell.com>; hayeswang@realtek.com; linux-
> kernel@vger.kernel.org; netdev@vger.kernel.org; linux-
> usb@vger.kernel.org; anthony.wong@canonical.com
> Subject: Re: [PATCH v6] r8152: Add support for setting pass through MAC
> address on RTL8153-AD
> 
> On Tuesday 14 June 2016 18:40:17 Greg KH wrote:
> > On Tue, Jun 14, 2016 at 06:28:10PM +0200, Pali Rohár wrote:
> > > On Saturday 11 June 2016 19:42:26 David Miller wrote:
> > > > From: Andrew Lunn <andrew@lunn.ch>
> > > > Date: Sat, 11 Jun 2016 17:39:21 +0200
> > > >
> > > > > What is still open is do we want to accept it at all? Do we
> > > > > accept the concept of putting the same MAC address on multiple
> > > > > interfaces at hotplug time? Do we trust BIOS vendors to not
> > > > > keep changing DSDT property name, since it is not
> > > > > standardised?
> > > > >
> > > > > Do we want this at all should be decided by somebody more
> > > > > senior then those passing comments on the code.
> > > >
> > > > Indeed, I think the behavior of using the same MAC address on
> > > > multiple interfaces if we plug several of these in at once is not
> > > > good.
> > > >
> > > > We shouldn't behave this way just because the Microsoft driver
> > > > does.
> > >
> > > I agree, but in some cases it is night mare for local admins when
> > > booting different OS cause changing MAC address on local network.
> > >
> > > Another similar situation: Imagine that you have two USB network
> > > cards and both have "burned" into their registers same MAC
> > > address. If you connect both those USB network cards, linux kernel
> > > bind appropriate driver which read MAC address for both those
> > > cards. But those addresses are same. What will linux kernel do in
> > > this case?
> >
> > If you can find such a broken USB device, try it and see :)
> 
> What do you mean by broken USB device?
> 
> You have never seen two ethernet cards with same MAC addresses? Right I
> have not seen two USB, but there is non zero chance that could happen.
> Specially now when more and more people starts using USB network cards.
> 
> > (hint, might be hard to find, I've never seen such a device before.)
> >
> > I don't see how that pertains to this issue, sorry, how does broken
> > USB hardware compare to a working Dell device?
> 
> It is same, how to handle two network cards which tell us, that they
> have same MAC addresses.
> 

The kernel handles this just fine.  In doing this patch I checked to see
what it does in that scenario.  Two devices are made.  systemd doesn't
rename the second device via the MAC name (eg enxAABBCCDDEEFF).