linux-kernel - Re: [PATCH net-next v6] net: phy: intel-xway: Add RGMII internal delay configuration

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Message-ID: <adb55f7dc3b4be01317cf7766e389874@dev.tdt.de>
Date:   Fri, 24 Feb 2023 09:48:06 +0100
From:   Martin Schiller <ms@....tdt.de>
To:     Michael Walle <michael@...le.cc>
Cc:     tharvey@...eworks.com, andrew@...n.ch, davem@...emloft.net,
        f.fainelli@...il.com, hauke@...ke-m.de, hkallweit1@...il.com,
        kuba@...nel.org, linux-kernel@...r.kernel.org,
        linux@...linux.org.uk, martin.blumenstingl@...glemail.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next v6] net: phy: intel-xway: Add RGMII internal
 delay configuration

On 2023-02-24 09:04, Michael Walle wrote:
> Hi Martin,
> 
> Am 2023-02-24 07:25, schrieb Martin Schiller:
>> On 2023-02-22 17:04, Michael Walle wrote:
>>> Hi Tim, Hi Martin,
>>> 
>>>> I've got some boards with the GPY111 phy on them and I'm finding 
>>>> that
>>>> modifying XWAY_MDIO_MIICTRL to change the skew has no effect unless 
>>>> I
>>>> do a soft reset (BCMR_RESET) first. I don't see anything in the
>>>> datasheet which specifies this to be the case so I'm interested it
>>>> what you have found. Are you sure adjusting the skews like this
>>>> without a soft (or hard pin based) reset actually works?
>>> 
>>> I do have the same PHY and I'm puzzled with the delay settings. Do
>>> you have an EEPROM attached to the PHY? According to my datasheet,
>>> that seems to make a difference. Apparently, only if there is an
>>> EEPROM, you can change the value (the value is then also written to
>>> the EEPROM according the datasheet).
>>> If you don't have one, the values will get overwritten by the
>>> external strappings on a soft reset. Therefore, it seems they cannot
>>> be set. (FWIW there is also a sticky bit, but that doesn't seem to
>>> help in this case).
>>> 
>>> -michael
>> 
>> Yes, you are right. The datasheet says: "In no-EEPROM mode, writing to
>> this register has no impact on operation of the device".
>> 
>> But changing this settings without an EEPROM indeed has an impact.
>> 
>> We don't use an EEPROM and without tuning this values some boards are
>> unable to communicate on the ethernet port(s).
> 
> Thanks for confirming! Could you share your PHYID1/PHYID2 register and
> firmware version (FWV, 0x1E) contents?

I've 2 PHYs integrated into the VR268 SoC which shows this values:

STD_PHYID1(reg 0x02): 0xd565
STD_PHYID2(reg 0x03): 0xa409
PHY_FWV   (reg 0x1E): 0x8435

And then there are 2 external GPY111 with this values:

STD_PHYID1(reg 0x02): 0xd565
STD_PHYID2(reg 0x03): 0xa401
PHY_FWV   (reg 0x1E): 0x8435

And one external GPY112 with this values:

STD_PHYID1(reg 0x02): 0xd565
STD_PHYID2(reg 0x03): 0xa401
PHY_FWV   (reg 0x1E): 0x8435

> 
> In our case, any changes in MIICTRL are lost after a soft reset.
> 
>> I varied these values during operation in the uboot and was able to 
>> test
>> the limits very nicely.
> 
> So I guess, the value you write into MIICTRL are retained on a soft 
> reset.

No, the value I write into MIICTRL are not retained on a soft reset.

> I.e.
> 
> mii write <phyad> 0x17 0xffff
> mii write <phyad> 0x00 0x8000
> mii read <phyad> 0x17
> 
> will still return 0xffff?

In my tests I always set the skew values in register 0x17 first and
then triggered a restart of the ANEG via register 0x0. This then led to
the new values being adopted.

> 
>> 
>> I wouldn't have introduced this feature if it hasn't got any impact.
> 
> Sure, I'm just trying to figure out the differences ;)
> 
> Thanks,
> Michael

- Martin