linux-kernel - Re: [PATCH v2 2/2] net: phy: motorcomm: Add pad drive strength cfg support

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Message-ID: <492b3874-7fcd-f7c1-bbe1-594c2d795854@starfivetech.com>
Date:   Thu, 18 May 2023 16:29:55 +0800
From:   Guo Samin <samin.guo@...rfivetech.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <netdev@...r.kernel.org>, Peter Geis <pgwipeout@...il.com>,
        Frank <Frank.Sae@...or-comm.com>,
        "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>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Yanhong Wang <yanhong.wang@...rfivetech.com>
Subject: Re: [PATCH v2 2/2] net: phy: motorcomm: Add pad drive strength cfg
 support

Re: [PATCH v2 2/2] net: phy: motorcomm: Add pad drive strength cfg support
From: Guo Samin <samin.guo@...rfivetech.com>
to: Andrew Lunn <andrew@...n.ch>
data: 2023/5/6

> 
> Re: [PATCH v2 2/2] net: phy: motorcomm: Add pad drive strength cfg support
> From: Andrew Lunn <andrew@...n.ch>
> to: Samin Guo <samin.guo@...rfivetech.com>
> data: 2023/5/5
> 
>>>  #define YTPHY_DTS_OUTPUT_CLK_DIS		0
>>> @@ -1495,6 +1504,7 @@ static int yt8531_config_init(struct phy_device *phydev)
>>>  {
>>>  	struct device_node *node = phydev->mdio.dev.of_node;
>>>  	int ret;
>>> +	u32 ds, val;
>>
>> Reverse Christmas tree.  Sort these longest first, shortest last.
>>
> Thanks, will fix.
>> Otherwise this looks O.K.
>>
>> The only open question is if real unit should be used, uA, not some
>> magic numbers. Lets see what the DT Maintainers say.
>>
>>       Andrew
> 
> Hi Andrew,
> 
> As I communicated with Frank, Motorcomm doesn't give specific units on their datasheet, except for magic numbers.
> Tried to ask Motorcomm last week, but it seems that they themselves do not know what the unit is and have no response so far.
> 
> 
> Below is all the relevant information I found：
> 
> Pad Drive Strength Cfg (EXT_0xA010)
> 
> Bit   |  Symbol           |  Access |  Default |  Description
> 15:13 |  Rgmii_sw_dr_rx   |  RW     |  0x3     |  Drive strenght of rx_clk pad.
>                                                |  3'b111: strongest; 3'b000: weakest.
> 
> 12    |  Rgmii_sw_dr[2]   |  RW     |  0x0     |  Bit 2 of Rgmii_sw_dr[2:0], refer to ext A010[5:4]
> 
> 5:4   |  Rgmii_sw_dr[1:0] |  RW     |  0x3     |  Bit 1 and 0 of Rgmii_sw_dr, Drive strenght of rxd/rx_ctl rgmii pad.
>                                                |  3'b111: strongest; 3'b000: weakest
> 
> 
> 
> Best regards,
> Samin

Hi Andrew,

We tried contacting motorcomm again, but so far we haven't been able to get any more information about unit.
Also, I found a similar configuration in Documentation/devicetree/bindings/net/qca,ar803x.yaml, and they also
used the 'magic numbers':

  qca,clk-out-strength:
    description: Clock output driver strength.
    $ref: /schemas/types.yaml#/definitions/uint32
    enum: [0, 1, 2]


Best regards,
Samin