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

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Date: Tue, 24 Oct 2023 09:56:43 +0200
From: Ante Knezic <ante.knezic@...mholz.de>
To: <o.rempel@...gutronix.de>
CC: <UNGLinuxDriver@...rochip.com>, <andrew@...n.ch>,
	<ante.knezic@...mholz.de>, <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 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?

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.

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