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

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Message-ID: <20210624130303.69234c5f@ktm>
Date:   Thu, 24 Jun 2021 13:03:03 +0200
From:   Lukasz Majewski <lukma@...x.de>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Madalin Bucur <madalin.bucur@....nxp.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Joakim Zhang <qiangqing.zhang@....com>,
        Vladimir Oltean <olteanv@...il.com>, netdev@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Mark Einon <mark.einon@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC 1/3] ARM: dts: imx28: Add description for L2 switch on XEA
 board

On Wed, 23 Jun 2021 17:36:59 -0700
Florian Fainelli <f.fainelli@...il.com> wrote:

> 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.

I see. Thanks for the explanation.

> 
> > 
> > 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.

For example, the imx287 SoC is still active product and is supposed
to be produced for at least 15 years after release. 

Best regards,

Lukasz Majewski

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