linux-kernel - Re: [PATCH net-next 2/2] ARM: dts: aspeed: elbert: Enable mac3 controller

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Date:   Tue, 6 Sep 2022 13:55:35 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Tao Ren <rentao.bupt@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Heyi Guo <guoheyi@...ux.alibaba.com>,
        Dylan Hung <dylan_hung@...eedtech.com>,
        Guangbin Huang <huangguangbin2@...wei.com>,
        Liang He <windhl@....com>, Hao Chen <chenhao288@...ilicon.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>, Tao Ren <taoren@...com>,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-aspeed@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH net-next 2/2] ARM: dts: aspeed: elbert: Enable mac3
 controller

On Mon, Sep 05, 2022 at 06:41:33PM -0700, Tao Ren wrote:
> Hi Andrew,
> 
> On Tue, Sep 06, 2022 at 02:22:50AM +0200, Andrew Lunn wrote:
> > On Mon, Sep 05, 2022 at 04:56:34PM -0700, rentao.bupt@...il.com wrote:
> > > From: Tao Ren <rentao.bupt@...il.com>
> > > 
> > > Enable mac3 controller in Elbert dts: Elbert MAC3 is connected to the
> > > onboard switch directly (fixed link).
> > 
> > What is the switch? Could you also add a DT node for it?
> > 
> > > 
> > > Signed-off-by: Tao Ren <rentao.bupt@...il.com>
> > > ---
> > >  arch/arm/boot/dts/aspeed-bmc-facebook-elbert.dts | 11 +++++++++++
> > >  1 file changed, 11 insertions(+)
> > > 
> > > diff --git a/arch/arm/boot/dts/aspeed-bmc-facebook-elbert.dts b/arch/arm/boot/dts/aspeed-bmc-facebook-elbert.dts
> > > index 27b43fe099f1..52cb617783ac 100644
> > > --- a/arch/arm/boot/dts/aspeed-bmc-facebook-elbert.dts
> > > +++ b/arch/arm/boot/dts/aspeed-bmc-facebook-elbert.dts
> > > @@ -183,3 +183,14 @@ imux31: i2c@7 {
> > >  &i2c11 {
> > >  	status = "okay";
> > >  };
> > > +
> > > +&mac3 {
> > > +	status = "okay";
> > > +	phy-mode = "rgmii";
> > 
> > 'rgmii' is suspicious, though not necessarily wrong. This value is
> > normally passed to the PHY, so the PHY inserts the RGMII delay. You
> > however don't have a PHY. So i assume the switch is inserting the
> > delay? Again, being able to see the DT properties for the switch would
> > be useful.
> > 
> >    Andrew
> 
> Thank you for the quick review!
> 
> The BMC mac3 is connected to BCM53134P's IMP_RGMII port, and there is no
> PHY between BMC MAC and BCM53134P. BCM53134P loads configurations from
> its EEPROM when the chip is powered.

So i assume you have the switch RGMII port doing the delays. That is
fine.

> Could you please point me an example showing how to describe the switch in
> dts? Anyhow I will need to improve the patch description and comments in
> v2.

It looks like drivers/net/dsa/b53 does not support this particular
switch. You could consider extending the driver. See

Documentation/devicetree/bindings/net/dsa/brcm,b53.yaml

for documentation of the binding.

    Andrew