netdev - Re: [PATCH v3 net] i40e: Look up MAC address in Open Firmware or IDPROM

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Date:	Fri, 30 Oct 2015 14:36:45 -0400
From:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:	"Nelson, Shannon" <shannon.nelson@...el.com>
Cc:	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	"Wyborny, Carolyn" <carolyn.wyborny@...el.com>,
	"Skidmore, Donald C" <donald.c.skidmore@...el.com>,
	"Vick, Matthew" <matthew.vick@...el.com>,
	"Ronciak, John" <john.ronciak@...el.com>,
	"Williams, Mitch A" <mitch.a.williams@...el.com>,
	"andy.shevchenko@...il.com" <andy.shevchenko@...il.com>
Subject: Re: [PATCH v3 net] i40e: Look up MAC address in Open Firmware or
 IDPROM

On (10/30/15 18:28), Nelson, Shannon wrote:
> 
> Going along with this being the equivalent of the ixgbe patch, I'd
> prefer the new code to be in i40e_main.c, rather than in i40e_common.c.
> In the design of our drivers, the common file is essentially a device
> specific layer, and the OS and platform related stuff should stay in
> i40e_main.c.  That would also take care of one of the include file nits
> that Andy mentioned.

ok, and that was my initial instinct as well, except that I noticed
that the existing i40e code tries interesting variations from the 
typical intel driver model by calling i40e_get_mac_addr() which lives in
(for reasons not obvious to me) i40e_common.c

So I assumed there must be some other deeper wisdom at work here.

> At the risk of flying my Device Tree ignorance for all to see, I have
> a couple questions on how this is used.
> 
> Since the mac address is specific to the individual device, how does it
> get into the device tree?  I thought the device tree was compiled ahead
> of time for the platform it is used on.  Is this a generic DT pattern
> just in case some platform actually has the mac-address?  Or does the
> device mac-address get saved into the DT on the first time through this
> path so it can be found next time?
> 
> If the Device Tree has a different mac address than the HW, when
> does the kernel tell the HW to use a different mac address?  Does the
> DT management eventually call the ndo_set_mac_address call so the HW
> knows to use a different mac address?

yes, and here I was hoping for some feedback from the intel folks as
well. Commit c762dff24c06 sets hw->mac.perm_addr. I dont know
if there is some similar i40e state that needs to be set.

Please share insights.

--Sowmini

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