netdev - Re: [RFC PATCH net-next] net: dsa: mt7530: rename MT7621 compatible

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Date:   Sat, 19 Dec 2020 21:48:31 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>, DENG Qingfang <dqfext@...il.com>,
        netdev@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Greg Ungerer <gerg@...nel.org>,
        Rene van Dorst <opensource@...rst.com>,
        John Crispin <john@...ozen.org>
Subject: Re: [RFC PATCH net-next] net: dsa: mt7530: rename MT7621 compatible

Hi Andrew, Florian,

On Sat, Dec 19, 2020 at 09:07:13AM -0800, Florian Fainelli wrote:
> On 12/19/2020 8:26 AM, Andrew Lunn wrote:
> >> --- a/drivers/net/dsa/mt7530.c
> >> +++ b/drivers/net/dsa/mt7530.c
> >> @@ -2688,7 +2688,7 @@ static const struct mt753x_info mt753x_table[] = {
> >>  };
> >>  
> >>  static const struct of_device_id mt7530_of_match[] = {
> >> -	{ .compatible = "mediatek,mt7621", .data = &mt753x_table[ID_MT7621], },
> >> +	{ .compatible = "mediatek,mt7621-gsw", .data = &mt753x_table[ID_MT7621], },
> >>  	{ .compatible = "mediatek,mt7530", .data = &mt753x_table[ID_MT7530], },
> >>  	{ .compatible = "mediatek,mt7531", .data = &mt753x_table[ID_MT7531], },
> >>  	{ /* sentinel */ },
> > 
> > This will break backwards compatibility with existing DT blobs. You
> > need to keep the old "mediatek,mt7621", but please add a comment that
> > it is deprecated.
> 
> Besides, adding -gsw would make it inconsistent with the existing
> matching compatible strings. While it's not ideal to have the same
> top-level SoC compatible and having another sub-node within that SoC's
> DTS have the same compatible, given this would be break backwards
> compatibility, cannot you stay with what is defined today?

The MT7621 device tree is in staging. I suppose that some amount of
breaking changes could be tolerated?

But Qingfang, I'm confused when looking at drivers/staging/mt7621-dts/mt7621.dtsi.

/ethernet@...00000/mdio-bus {
	switch0: switch0@0 {
		compatible = "mediatek,mt7621";
		#address-cells = <1>;
		#size-cells = <0>;
		reg = <0>;
		mediatek,mcm;
		resets = <&rstctrl 2>;
		reset-names = "mcm";

		ports {
			#address-cells = <1>;
			#size-cells = <0>;
			reg = <0>;
			port@0 {
				status = "off";
				reg = <0>;
				label = "lan0";
			};
			port@1 {
				status = "off";
				reg = <1>;
				label = "lan1";
			};
			port@2 {
				status = "off";
				reg = <2>;
				label = "lan2";
			};
			port@3 {
				status = "off";
				reg = <3>;
				label = "lan3";
			};
			port@4 {
				status = "off";
				reg = <4>;
				label = "lan4";
			};
			port@6 {
				reg = <6>;
				label = "cpu";
				ethernet = <&gmac0>;
				phy-mode = "trgmii";
				fixed-link {
					speed = <1000>;
					full-duplex;
				};
			};
		};
	};
};

/ {
	gsw: gsw@...10000 {
		compatible = "mediatek,mt7621-gsw";
		reg = <0x1e110000 0x8000>;
		interrupt-parent = <&gic>;
		interrupts = <GIC_SHARED 23 IRQ_TYPE_LEVEL_HIGH>;
	};
};

What is the platform device at the memory address 1e110000?
There is no driver for it. The documentation only has me even more
confused:

Mediatek Gigabit Switch
=======================

The mediatek gigabit switch can be found on Mediatek SoCs (mt7620, mt7621).

Required properties:
- compatible: Should be "mediatek,mt7620-gsw" or "mediatek,mt7621-gsw"
- reg: Address and length of the register set for the device
- interrupts: Should contain the gigabit switches interrupt
- resets: Should contain the gigabit switches resets
- reset-names: Should contain the reset names "gsw"

Example:

gsw@...10000 {
	compatible = "ralink,mt7620-gsw";     <- notice how even the example is bad and inconsistent
	reg = <0x10110000 8000>;

	resets = <&rstctrl 23>;
	reset-names = "gsw";

	interrupt-parent = <&intc>;
	interrupts = <17>;
};

Does the MT7621 contain two Ethernet switches, one accessed over MMIO
and another over MDIO? Or is it the same switch? I don't understand.
What is the relationship between the new compatible that you're
proposing, Qingfang, and the existing device tree bindings?