linux-kernel - Re: [net-next: PATCH 09/12] Documentation: ACPI: DSD: introduce DSA description

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Date:   Wed, 22 Jun 2022 12:22:23 +0200
From:   Marcin Wojtas <mw@...ihalf.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>, vivien.didelot@...il.com,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>, pabeni@...hat.com,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Grzegorz Bernacki <gjb@...ihalf.com>,
        Grzegorz Jaszczyk <jaz@...ihalf.com>,
        Tomasz Nowicki <tn@...ihalf.com>,
        Samer El-Haj-Mahmoud <Samer.El-Haj-Mahmoud@....com>,
        upstream@...ihalf.com
Subject: Re: [net-next: PATCH 09/12] Documentation: ACPI: DSD: introduce DSA description

śr., 22 cze 2022 o 11:24 Andrew Lunn <andrew@...n.ch> napisał(a):
>
> On Wed, Jun 22, 2022 at 11:08:13AM +0200, Marcin Wojtas wrote:
> > wt., 21 cze 2022 o 13:42 Andy Shevchenko
> > <andriy.shevchenko@...ux.intel.com> napisał(a):
> > >
> > > On Tue, Jun 21, 2022 at 01:18:38PM +0200, Andrew Lunn wrote:
> > > > On Tue, Jun 21, 2022 at 02:09:14PM +0300, Andy Shevchenko wrote:
> > > > > On Mon, Jun 20, 2022 at 09:47:31PM +0200, Andrew Lunn wrote:
> > >
> > > ...
> > >
> > > > > > > +        Name (_CRS, ResourceTemplate ()
> > > > > > > +        {
> > > > > > > +            Memory32Fixed (ReadWrite,
> > > > > > > +                0xf212a200,
> > > > > > > +                0x00000010,
> > > > > >
> > > > > > What do these magic numbers mean?
> > > > >
> > > > > Address + Length, it's all described in the ACPI specification.
> > > >
> > > > The address+plus length of what? This device is on an MDIO bus. As
> > > > such, there is no memory! It probably makes sense to somebody who
> > > > knows ACPI, but to me i have no idea what it means.
> > >
> > > I see what you mean. Honestly I dunno what the device this description is for.
> > > For the DSA that's behind MDIO bus? Then it's definitely makes no sense and
> > > MDIOSerialBus() resources type is what would be good to have in ACPI
> > > specification.
> > >
> >
> > It's not device on MDIO bus, but the MDIO controller's register itself
>
> Ah. So this is equivalent to
>
>                 CP11X_LABEL(mdio): mdio@...200 {
>                         #address-cells = <1>;
>                         #size-cells = <0>;
>                         compatible = "marvell,orion-mdio";
>                         reg = <0x12a200 0x10>;
>                         clocks = <&CP11X_LABEL(clk) 1 9>, <&CP11X_LABEL(clk) 1 5>,
>                                  <&CP11X_LABEL(clk) 1 6>, <&CP11X_LABEL(clk) 1 18>;
>                         status = "disabled";
>                 };
>
> DT seems a lot more readable, "marvell,orion-mdio" is a good hint that
> device this is. But maybe it is more readable because that is what i'm
> used to.

No worries, this reaction is not uncommon (including myself), I agree
it becomes more readable, the longer you work with it :).

IMO the ACPI node of orion-mdio looks very similar. Please take a look:

        Device (SMI0)
        {
            Name (_HID, "MRVL0100")              // _HID: Hardware ID
            Name (_UID, 0x00)                          // _UID: Unique ID
            Method (_STA)                                 // _STA: Device status
            {
                Return (0xF)
            }
            Name (_CRS, ResourceTemplate ()
            {
                Memory32Fixed (ReadWrite,
                    0xf212a200,                        // Address Base
                    0x00000010,                       // Address Length
                    )
            })
        }

You can "map" the objects/methods to what you know from DT farly easily:
_HID -> compatible string
_STA -> 'status' property
_CRS & Memory32Fixed  -> 'reg' property (_CRS can also comprise IRQs
and other kind of resources, you can check [1] for more details).

Clocks are configured by firmware, so they are not referenced in the
tables and touched by the orion-mdio driver.

>
> Please could you add a lot more comments. Given that nobody currently
> actually does networking via ACPI, we have to assume everybody trying
> to use it is a newbie, and more comments are better than less.

I can add more verbose description of the example and probably a
reference to https://www.kernel.org/doc/Documentation/firmware-guide/acpi/dsd/phy.rst
("DSDT entry for MDIO node").

[1] https://uefi.org/specs/ACPI/6.4/06_Device_Configuration/Device_Configuration.html#crs-current-resource-settings

Best regards,
Marcin

>
> Thanks
>         Andrew