linux-kernel - Re: [PATCH RFC v1 1/4] dt-bindings: net: dwmac-meson: use picoseconds for the RGMII RX delay

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Date:   Sun, 15 Nov 2020 16:37:23 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     davem@...emloft.net, kuba@...nel.org,
        linux-amlogic@...ts.infradead.org, devicetree@...r.kernel.org,
        robh+dt@...nel.org, jianxin.pan@...ogic.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        khilman@...libre.com, Neil Armstrong <narmstrong@...libre.com>,
        jbrunet@...libre.com
Subject: Re: [PATCH RFC v1 1/4] dt-bindings: net: dwmac-meson: use
 picoseconds for the RGMII RX delay

On Sun, Nov 15, 2020 at 10:22:06AM +0100, Martin Blumenstingl wrote:
> Hi Andrew,
> 
> On Sat, Nov 14, 2020 at 11:32 PM Andrew Lunn <andrew@...n.ch> wrote:
> [...]
> > > +        amlogic,rgmii-rx-delay-ps:
> > > +          default: 0
> > >            description:
> > >              The internal RGMII RX clock delay (provided by this IP block) in
> > > -            nanoseconds. When phy-mode is set to "rgmii" then the RX delay
> > > +            picoseconds. When phy-mode is set to "rgmii" then the RX delay
> > >              should be explicitly configured. When the phy-mode is set to
> > >              either "rgmii-id" or "rgmii-rxid" the RX clock delay is already
> > >              provided by the PHY. Any configuration is ignored when the
> > >              phy-mode is set to "rmii".
> >
> > Hi Martin
> >
> > I don't think the wording matches what the driver is actually doing:
> >
> >         if (dwmac->rx_delay_ns == 2)
> >                 rx_dly_config = PRG_ETH0_ADJ_ENABLE | PRG_ETH0_ADJ_SETUP;
> >         else
> >                 rx_dly_config = 0;
> >
> >         switch (dwmac->phy_mode) {
> >         case PHY_INTERFACE_MODE_RGMII:
> >                 delay_config = tx_dly_config | rx_dly_config;
> >                 break;
> >         case PHY_INTERFACE_MODE_RGMII_RXID:
> >                 delay_config = tx_dly_config;
> >                 break;
> >         case PHY_INTERFACE_MODE_RGMII_TXID:
> >                 delay_config = rx_dly_config;
> >                 break;
> >         case PHY_INTERFACE_MODE_RGMII_ID:
> >         case PHY_INTERFACE_MODE_RMII:
> >                 delay_config = 0;
> >                 break;
> >
> > So rx_delay is used for both rgmii and rgmii-txid. The binding says
> > nothing about rgmii-txid.
> interesting point here. it's been like this before this patch. still I
> would like to understand what the proper way to fix it is so I can
> also include a fix for it:
> 1. should rgmii-txid not add any RX delay on the MAC side? that would
> mean for my board I will switch to phy-mode rgmii so the MAC applies
> both the RX and TX delays
> 2. update the documentation to clarify that rgmii-txid would also add
> the RX delay on the MAC side

Hi Martin

I would fix the documentation.

> that is a good point and also a bug with one of the previous patches
> I'll include a patch fixing this in v2

Thanks for looking at these.

       Andrew