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

[Michael Walle]

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?

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.
I.e.

mii write <phyad> 0x17 0xffff
mii write <phyad> 0x00 0x8000
mii read <phyad> 0x17

will still return 0xffff?

> 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