Date:   Fri, 10 May 2019 13:28:22 +0200
From:   Petr Štetiar <ynezz@...e.cz>
To:     Andy Duan <fugang.duan@....com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "john@...ozen.org" <john@...ozen.org>,
        "bgolaszewski@...libre.com" <bgolaszewski@...libre.com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Alban Bedel <albeu@...e.fr>, devicetree@...r.kernel.org
Subject: Re: [PATCH net 0/3] add property "nvmem_macaddr_swap" to swap
 macaddr bytes order

Andy Duan <fugang.duan@....com> [2019-05-10 08:23:58]:

Hi Andy,

you've probably forget to Cc some maintainers and mailing lists, so I'm
adding them now to the Cc loop. This patch series should be posted against
net-next tree as per netdev FAQ[0], but you've to wait little bit as
net-next is currently closed for the new submissions and you would need to
resend it anyway.

0. https://www.kernel.org/doc/html/latest/networking/netdev-FAQ.html

> ethernet controller driver call .of_get_mac_address() to get
> the mac address from devictree tree, if these properties are
> not present, then try to read from nvmem. i.MX6x/7D/8MQ/8MM
> platforms ethernet MAC address read from nvmem ocotp eFuses,
> but it requires to swap the six bytes order.

Thanks for bringing up this topic, as I would like to extend the
functionality as well, but I'm still unsure how to tackle this and where,
so I'll (ab)use this opportunity to bring other use cases I would like to
cover in the future, so we could better understand the needs.

This reverse byte order format/layout is one of a few other storage formats
currently used by vendors, some other (creative) vendors are currently
providing MAC addresses in NVMEMs as ASCII text in following two formats
(hexdump -C /dev/mtdX):

 a) 0090FEC9CBE5 - MAC address stored as ASCII without colon between octets

  00000090  57 2e 4c 41 4e 2e 4d 41  43 2e 41 64 64 72 65 73  |W.LAN.MAC.Addres|
  000000a0  73 3d 30 30 39 30 46 45  43 39 43 42 45 35 00 48  |s=0090FEC9CBE5.H|
  000000b0  57 2e 4c 41 4e 2e 32 47  2e 30 2e 4d 41 43 2e 41  |W.LAN.2G.0.MAC.A|

  (From https://github.com/openwrt/openwrt/pull/1448#issuecomment-442476695)

 b) D4:EE:07:33:6C:20 - MAC address stored as ASCII with colon between octets

  00000180  66 61 63 5f 6d 61 63 20  3d 20 44 34 3a 45 45 3a  |fac_mac = D4:EE:|
  00000190  30 37 3a 33 33 3a 36 43  3a 32 30 0a 42 44 49 4e  |07:33:6C:20.BDIN|

  (From https://github.com/openwrt/openwrt/pull/1906#issuecomment-483881911)

> The patch set is to add property "nvmem_macaddr_swap" to swap
> macaddr bytes order.

so it would allow following DT construct (simplified):

 &eth0 {
	nvmem-cells = <&eth0_addr>;
	nvmem-cell-names = "mac-address";
	nvmem_macaddr_swap;
 };

I'm not sure about the `nvmem_macaddr_swap` property name, as currently there
are no other properties with underscores, so it should be probably named as
`nvmem-macaddr-swap`. DT specs permits use of the underscores, but the
estabilished convention is probably prefered.

In order to cover all above mentioned use cases, it would make more sense
to add a description of the MAC address layout to the DT and use this
information to properly postprocess the NVMEM content into usable MAC
address?

Something like this?

 - nvmem-cells: phandle, reference to an nvmem node for the MAC address
 - nvmem-cell-names: string, should be "mac-address" if nvmem is to be used
 - nvmem-mac-address-layout: string, specifies MAC address storage layout.
   Supported values are: "binary", "binary-swapped", "ascii", "ascii-delimited".
   "binary" is the default.

Or perhaps something like this?

 - nvmem-cells: phandle, reference to an nvmem node for the MAC address
 - nvmem-cell-names: string, should be any of the supported values.
   Supported values are: "mac-address", "mac-address-swapped",
   "mac-address-ascii", "mac-address-ascii-delimited".

I'm more inclined towards the first proposed solution, as I would like to
propose MAC address octet incrementation feature in the future, so it would
become:

 - nvmem-cells: phandle, reference to an nvmem node for the MAC address
 - nvmem-cell-names: string, should be "mac-address" if nvmem is to be used
 - nvmem-mac-address-layout: string, specifies MAC address storage layout.
   Supported values are: "binary", "binary-swapped", "ascii", "ascii-delimited".
   "binary" is the default.
 - nvmem-mac-address-increment: number, value by which should be
   incremented MAC address octet, could be negative value as well.
 - nvmem-mac-address-increment-octet: number, valid values 0-5, default is 5.
   Specifies MAC address octet used for `nvmem-mac-address-increment`.

What do you think?

Cheers,

Petr

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