linux-kernel - Re: [PATCH v2 net-next] sky2: use random address if EEPROM is bad

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Date:	Wed, 12 Aug 2015 08:28:23 -0700
From:	Stephen Hemminger <stephen@...workplumber.org>
To:	Liviu Dudau <Liviu.Dudau@....com>
Cc:	Florian Fainelli <f.fainelli@...il.com>,
	Mirko Lindner <mlindner@...vell.com>,
	"ryan.harkin@...aro.org" <ryan.harkin@...aro.org>,
	netdev <netdev@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 net-next] sky2: use random address if EEPROM is bad

On Wed, 12 Aug 2015 10:30:05 +0100
Liviu Dudau <Liviu.Dudau@....com> wrote:

> On Tue, Aug 11, 2015 at 06:01:32PM +0100, Stephen Hemminger wrote:
> > On Tue, 11 Aug 2015 15:35:56 +0100
> > Liviu Dudau <Liviu.Dudau@....com> wrote:
> > 
> > > On some embedded systems the EEPROM does not contain a valid MAC address.
> > > In that case it is better to fallback to a generated mac address and
> > > let init scripts fix the value later.
> > > 
> > > Reported-by: Liviu Dudau <Liviu.Dudau@....com>
> > > Signed-off-by: Stephen Hemminger <stephen@...workplumber.org>
> > > [Changed handcoded setup to use eth_hw_addr_random() instead]
> > > Signed-off-by: Liviu Dudau <Liviu.Dudau@....com>
> > > ---
> > > I have tested this on my Juno platform and I can successfully do an nfsroot boot.
> > > 
> > > Best regards,
> > > Liviu
> > > 
> > >  drivers/net/ethernet/marvell/sky2.c | 7 +++++++
> > >  1 file changed, 7 insertions(+)
> > > 
> > > diff --git a/drivers/net/ethernet/marvell/sky2.c b/drivers/net/ethernet/marvell/sky2.c
> > > index d9f4498..c309879 100644
> > > --- a/drivers/net/ethernet/marvell/sky2.c
> > > +++ b/drivers/net/ethernet/marvell/sky2.c
> > > @@ -4819,6 +4819,13 @@ static struct net_device *sky2_init_netdev(struct sky2_hw *hw, unsigned port,
> > >  		memcpy_fromio(dev->dev_addr, hw->regs + B2_MAC_1 + port * 8,
> > >  			      ETH_ALEN);
> > >  
> > > +	/* if the address is invalid, use a random value */
> > > +	if (!is_valid_ether_addr(dev->dev_addr)) {
> > > +		netdev_warn(dev,
> > > +			"Invalid MAC address, defaulting to random\n");
> > > +		eth_hw_addr_random(dev);
> > > +	}
> > > +
> > >  	return dev;
> > >  }
> > >  
> > 
> > This is not enough, you need to program the hardware with the new random MAC
> > address. The easiest way is calling sky2_set_mac_address, but you need to convert
> > the address from array back to sockaddr.
> > 
> 
> OK, I am a bit confused as to why sky2_set_mac_address is needed here, as this was not
> required by the existing function. Given that in my tests I get a random MAC address
> assigned every time to the device and I can see the same MAC address with ifconfig, how
> can I test the effect of sky2_set_mac_address if I add it?

The network device address is stored in two places. One is in the
kernel (dev->dev_addr) and is  used by networking stack.
The other is the hardware (actually two places) and is used filtering received packets
in the PHY and for sending hardware generated pause frames.

When a random address is generated, you need to tell the hardware
to use that address as well. I suspect your hardware maybe limited in functionality
and not do the normal filtering.
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