linux-kernel - Re: [RFC PATCH v2 3/8] net: sparx5: add hostmode with phylink support

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Date:   Wed, 23 Dec 2020 22:05:21 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Steen Hegelund <steen.hegelund@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Bjarni Jonasson <bjarni.jonasson@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        Madalin Bucur <madalin.bucur@....nxp.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Mark Einon <mark.einon@...il.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC PATCH v2 3/8] net: sparx5: add hostmode with phylink support

On Wed, Dec 23, 2020 at 09:58:52PM +0100, Alexandre Belloni wrote:
> On 22/12/2020 15:41:41+0100, Andrew Lunn wrote:
> > > Yes the register based injection/extration is not going to be fast, but
> > > the FDMA and its driver is being sent later as separate series to keep
> > > the size of this review down.
> > 
> > FDMA?
> > 
> > I need a bit more background here, just to make use this should be a
> > pure switchdev driver and not a DSA driver.
> > 
> 
> I don't think this should be a DSA driver. As for Ocelot, the CPU
> port is not a MAC and in that use case, this would be like a top of the
> rack switch with traffic going to the CPU port being mostly used for
> managmement (dhcp, stp, etc...) as opposed to being used to forward
> traffic to another interface, like WAN or wifi.
> 
> However, I would think there will be cases where the internal CPU is not
> use and instead use ths switch in a DSA setting, very much like what is
> done for Felix with regards to Ocelot.

>From what i have heard so far, it does seem like a pure switchdev
driver is correct. So long as FDMA is not a standalone Ethernet
driver, but just a DMA engine incorporated into this driver, the
architecture looks correct.

I was asking because from the information that was available, it was
impossible to say what the correct architecture should be.

     Andrew