Re: [RFC 1/3] ARM: dts: imx28: Add description for L2 switch on XEA board

[Florian Fainelli <f.fainelli@gmail.com>]

On 6/23/2021 8:26 AM, Lukasz Majewski wrote:
> Hi Andrew,
> 
>> On Tue, Jun 22, 2021 at 10:51:34PM +0200, Lukasz Majewski wrote:
>>> Hi Andrew,
>>>
>>>> On Tue, Jun 22, 2021 at 04:41:09PM +0200, Lukasz Majewski wrote:
>>>>> The 'eth_switch' node is now extendfed to enable support for L2
>>>>> switch.
>>>>>
>>>>> Moreover, the mac[01] nodes are defined as well and linked to
>>>>> the former with 'phy-handle' property.
>>>>
>>>> A phy-handle points to a phy, not a MAC! Don't abuse a well known
>>>> DT property like this.
>>>
>>> Ach.... You are right. I will change it.
>>>
>>> Probably 'ethernet' property or 'link' will fit better?
>>
>> You should first work on the overall architecture. I suspect you will
>> end up with something more like the DSA binding, and not have the FEC
>> nodes at all. Maybe the MDIO busses will appear under the switch?
>>
>> Please don't put minimal changes to the FEC driver has your first
>> goal. We want an architecture which is similar to other switchdev
>> drivers. Maybe look at drivers/net/ethernet/ti/cpsw_new.c.
> 
> I'm a bit confused - as I thought that with switchdev API I could just
> extend the current FEC driver to add bridge offload.
> This patch series shows that it is doable with little changes
> introduced.

Regardless of how you end up implementing the switching part in the 
driver, one thing that you can use is the same DT binding as what DSA 
uses as far as representing ports of the Ethernet controller. That means 
that ports should ideally be embedded into an 'ethernet-ports' container 
node, and you describe each port individually as sub-nodes and provide, 
when appropriate 'phy-handle' and 'phy-mode' properties to describe how 
the Ethernet PHYs are connected.

> 
> However, now it looks like I would need to replace FEC driver and
> rewrite it in a way similar to cpsw_new.c, so the switchdev could be
> used for both cases - with and without L2 switch offload.
> 
> This would be probably conceptually correct, but i.MX FEC driver has
> several issues to tackle:
> 
> - On some SoCs (vf610, imx287, etc.) the ENET-MAC ports don't have the
>    same capabilities (eth1 is a bit special)
> 
> - Without switch we need to use DMA0 and DMA1 in the "bypass" switch
>    mode (default). When switch is enabled we only use DMA0. The former
>    case is best fitted with FEC driver instantiation. The latter with
>    DSA or switchdev.
> 
>> The cpsw
>> driver has an interesting past, it did things the wrong way for a long
>> time, but the new switchdev driver has an architecture similar to what
>> the FEC driver could be like.
>>
>> 	Andrew
> 
> Maybe somebody from NXP can provide input to this discussion - for
> example to sched some light on FEC driver (near) future.

Seems like some folks at NXP are focusing on the STMMAC controller these 
days (dwmac from Synopsys), so maybe they have given up on having their 
own Ethernet MAC for lower end products.
-- 
Florian