netdev - Re: [PATCH net-next v4 2/2] net:dsa:microchip: add property to select

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Date: Tue, 24 Oct 2023 12:09:15 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Ante Knezic <ante.knezic@...mholz.de>
Cc: UNGLinuxDriver@...rochip.com, andrew@...n.ch, conor+dt@...nel.org,
	davem@...emloft.net, devicetree@...r.kernel.org,
	edumazet@...gle.com, f.fainelli@...il.com,
	krzysztof.kozlowski+dt@...aro.org, kuba@...nel.org,
	linux-kernel@...r.kernel.org, marex@...x.de, netdev@...r.kernel.org,
	olteanv@...il.com, pabeni@...hat.com, robh+dt@...nel.org,
	woojung.huh@...rochip.com
Subject: Re: [PATCH net-next v4 2/2] net:dsa:microchip: add property to select

On Tue, Oct 24, 2023 at 09:56:43AM +0200, Ante Knezic wrote:
> On Mon, 23 Oct 2023 16:36:35 +0200, Oleksij Rempel wrote:
> > If I see it correctly, in both cases there is only one bit to configure
> > direction. The code need to support two interface modes:
> > - PHY_INTERFACE_MODE_RMII (MAC mode) PLL is the clock provider. REFCLKO
> >  is used.
> > - PHY_INTERFACE_MODE_REVRMII (PHY mode) PLL is not used, REFCLKI is the
>    clock provider.
> 
> As you suggested, it looks like KSZ9897 clocking mode depends on RMII interface
> mode (with strapping pins), but I don't see this for KSZ8863. The PHY/MAC mode
> is selected with Register 0x35 bit 7 and the clocking mode is selected via
> strapping pins EN_REFCLKO and SMTXD32 (and additional register 0xC6 bit 3).
> I guess its possible for the KSZ8863 to be the clock provider/consumer
> regardless of PHY/MAC mode?

Register 0x35 bit 7 is for MII mode
Register 0xC6 bit 3 is for RMII mode

MII != RMII

> Table 3-5: RMII CLOCK SETTING of KSZ8863 datasheet describes the available 
> clocking modes. If we try to create a relation between KSZ9897 and KSZ8863:
> 
> KSZ9897 "Normal Mode" is equivalent to KSZ8863 mode described in first column
> of table 3-5: 
> - EN_REFCLKO = 0, 0xC6(3) = 0 -> external 50Mhz OSC input to REFCLKI and X1 
>   pin directly
> 
> KSZ9897 "Clock Mode" is equivalent to KSZ8863 mode described in fourth/fifth 
> column (difference is only clock frequency) of table 3-5:
> - EN_REFCLKO = 1, 0xC6(3) = 1 -> 50/25Mhz on X1 pin, 50/25Mhz RMII clock goes
>   to REFCLKI internally. REFCLKI can be pulled down by resistor.
> 
> That leaves us with additional columns 2 and 3 of table 3-5 for KSZ8863, that
> are similar to KSZ9897 Clock mode, but REFCLKI needs to be fed externally from
> REFCLKO.

All of 5 variants described in "Table 3-5: RMII CLOCK SETTING of KSZ8863"
can be boiled down to two main configurations:

REFCLKI is used as clock source for internal MAC == Normal Mode or
RevRMII mode.
REFCLKI is not used as clock source for internal MAC == Clock Mode or
RMII mode.

Variants 1, 2, 3 describe only how can we feed REFCLKI from outside of
the chip. Even variant 2 and 3 make the switch to be an actually
physical clock provider, we still need to use REFCLKI and wire it
outside of the chip which make it practically a Normal Mode or RevRMII mode.

> > I already did some work to configure CPU interface, where which can be at least
> > partially reused for your work:
> > https://lore.kernel.org/all/20230517121034.3801640-2-o.rempel@pengutronix.de/
> > (Looks I forgot to complete mainlining for this patch)
> > 
> > If implanted as described, no new devicetree properties will be needed.
> 
> I don't quite get how the proposed patch might effect this topic?

You will need to add ksz8_phylink_mac_link_up() as this patch already
dose.

> By setting PHY/MAC mode? As noted, I dont see the same relation between clock and
> MII mode for KSZ8863 as for KSZ9897? 

I hope current mail will clear it.

Regards,
Oleksij
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