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

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Date:   Mon, 16 Jan 2023 10:49:43 +0800
From:   "Frank.Sae" <Frank.Sae@...or-comm.com>
To:     Andrew Lunn <andrew@...n.ch>
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

Hi Andrew,

On 2023/1/11 21:07, Andrew Lunn wrote:
>> 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.

The standard type of rx-internal-delay-ps is uint32-array, so it can't
be -150.

https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/property-units.yaml

 "-ps$":
    $ref: types.yaml#/definitions/uint32-array
    description: picosecond


Can we used rx-internal-delay-ps with int32 type?
like this:
  rx-internal-delay-ps:
    $ref: /schemas/types.yaml#/definitions/int32
    enum: [ -1900, -1750, -1600, -1450, -1300, -1150, -1000, -850, -700,
-550, -400, -250, -100, 0, 50, 150, 200, 300, 350, 450, 600, 750, 900,
1050, 1200, 1350, 1500, 1650, 1800, 1950, 2100, 2250 ]
    default: 0


> 
>> 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

Tanks. We will remove tx-clk-xxxx-inverted and tx-clk-adj-enabled.