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Date:   Sun, 20 Dec 2020 09:49:36 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     DENG Qingfang <dqfext@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>, netdev <netdev@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <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

On Sun, Dec 20, 2020 at 12:48:08PM +0800, DENG Qingfang wrote:
> Hi Vladimir,
> 
> On Sun, Dec 20, 2020 at 3:48 AM Vladimir Oltean <olteanv@...il.com> wrote:
> >
> > 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?
> 
> The current dtsi is copied from OpenWrt, so the existing "mt7621-gsw"
> / "mt7620-gsw" compatible is for their swconfig driver.
> MT7621 has only one switch, accessed over MDIO, so the reg property
> has no effect.
> 
> Should this patch be accepted, the existing gsw nodes can be dropped.

But still, what is at memory address 0x1e110000, if the switch is
accessed over MDIO?

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