linux-kernel - Re: [PATCH net-next v1 1/3] dt-bindings: net: Add Motorcomm yt8xxx ethernet phy Driver bindings

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Message-ID: <Y760k6/pKdjwu1fU@lunn.ch>
Date:   Wed, 11 Jan 2023 14:07:31 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     "Frank.Sae" <Frank.Sae@...or-comm.com>
Cc:     Peter Geis <pgwipeout@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        xiaogang.fan@...or-comm.com, fei.zhang@...or-comm.com,
        hua.sun@...or-comm.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH net-next v1 1/3] dt-bindings: net: Add Motorcomm yt8xxx
 ethernet phy Driver bindings

> RX delay = rx-delay-basic (0ns or 1.9ns) + x-delay-additional-ps
> (N*150ps, N = 0 ~ 15)
>  If rx-delay-basic is removed and controlled by phy-mode.
>  when phy-mode is  rgmii-id or rgmii-rxid, RX delay is 1.9ns + N*150ps.
>  But sometimes 1.9ns is still too big, we just need  0ns + N*150ps.
> 
> For this case, can we do like following ?
> rx-internal-delay-ps:
>     enum: [ 0, 150, 300, 450, 600, 750, 900, 1050, 1200, 1350, 1500,
> 1650, 1800, 1900, 1950, 2050, 2100, 2200, 2250, 2350, 2500, 2650, 2800,
> 2950, 3100, 3250, 3400, 3550, 3700, 3850, 4000, 4150 ]
>     default: 0
>  rx-internal-delay-ps is 0ns + N*150ps and  1.9ns + N*150ps.
>  And check whether need rx-delay-basic (1.9ns) by the val of
> rx-internal-delay-ps?

Nothing says delays are only positive. So you could have rgmii-id or
rgmii-rxid and a rx-internal-delay-ps of -150, if you need less than
1.9ns.

As i said, rx-internal-delay-ps is used to fine tune the delay.

> We can't reduce this down to tx-clk-inverted.
> There are two mac and two yt8531 on their board. Each of yt8531 need
> different config in DTS. They need adjust tx clk delay in
> link_change_notify callback function according to current speed.
> 
>  They configured tx-clk-xxxx-inverted like this :
> 
>     speed     GMAC0             GMAC1
>     1000M      1                  0		tx-clk-1000-inverted
>     100M       1                  1		tx-clk-100-inverted
>     10M       0/1                0/1     	tx-clk-10-inverted

What MAC is this? It seems very oddly designed, getting close to
broken. I've not seen any other MAC/PHY combination need anything like
this. 

> Can we put tx-clk-adj-enabled, tx-clk-10-inverted, tx-clk-100-inverted
> and tx-clk-1000-inverted in tx-clk-10-inverted like bit in byte?

No, they are individual boolean properties, so should be kept as they
are. But i really think somebody should be looking deep into the MAC
design to understand why it is like this, and if the MAC can sort out
this mess itself.

	Andrew