linux-kernel - Re: [PATCH v7 3/3] platform/chrome: cros_ec

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Message-ID: <CAHQZ30Dm1XbcQXjKXAfWUimL7NzYS8tkfwANpnB8kVRORsAjzw@mail.gmail.com>
Date:   Wed, 30 Nov 2022 09:52:29 -0700
From:   Raul Rangel <rrangel@...omium.org>
To:     Tzung-Bi Shih <tzungbi@...nel.org>
Cc:     Mark Hasemeyer <markhas@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Bhanu Prakash Maiya <bhanumaiya@...omium.org>,
        Benson Leung <bleung@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Guenter Roeck <groeck@...omium.org>,
        chrome-platform@...ts.linux.dev
Subject: Re: [PATCH v7 3/3] platform/chrome: cros_ec_uart: Add DT enumeration support

On Wed, Nov 30, 2022 at 12:10 AM Tzung-Bi Shih <tzungbi@...nel.org> wrote:
>
> On Tue, Nov 29, 2022 at 11:13:04AM -0700, Mark Hasemeyer wrote:
> > > > @@ -392,6 +393,12 @@ static int __maybe_unused cros_ec_uart_resume(struct device *dev)
> > > >  static SIMPLE_DEV_PM_OPS(cros_ec_uart_pm_ops, cros_ec_uart_suspend,
> > > >                        cros_ec_uart_resume);
> > > >
> > > > +static const struct of_device_id cros_ec_uart_of_match[] = {
> > > > +     { .compatible = "google,cros-ec-uart" },
> > > > +     {}
> > > > +};
> > > > +MODULE_DEVICE_TABLE(of, cros_ec_uart_of_match);
> > >
> > > It would need a guard for checking CONFIG_OF.  Similar to what
> > > `cros_ec_uart_acpi_id` does.
> > >
> > > > @@ -405,6 +412,7 @@ static struct serdev_device_driver cros_ec_uart_driver = {
> > > >       .driver = {
> > > >               .name   = "cros-ec-uart",
> > > >               .acpi_match_table = ACPI_PTR(cros_ec_uart_acpi_id),
> > > > +             .of_match_table = cros_ec_uart_of_match,
> > >
> > > It would need be wrapped by `of_match_ptr()`.  Similar to what
> > > `ACPI_PTR()` does.
> >
> > I'm not sure we want a guard in this case because we compile the kernel without
> > CONFIG_OF enabled for (most?) x86 platforms. Yet we still need the device
> > tree code to enumerate using the PRP0001 _HID method.
>

> I'm not familiar to ACPI.  However, I thought it should add the compatible
> string in the _DSD instead of using of_match for the case.  See example
> in [1].
>
> [1]: https://www.kernel.org/doc/html/latest/firmware-guide/acpi/enumeration.html#device-tree-namespace-link-device-id

Correct, we need to add the compatible string inside the _DSD. This is
what we currently do for all of our released devices:
```
    Device (CRFP)
    {
        Name (_HID, "PRP0001")  // _HID: Hardware ID
        Name (_UID, Zero)  // _UID: Unique ID
        Name (_DDN, "Fingerprint Reader")  // _DDN: DOS Device Name
        Name (_DSD, Package (0x02)  // _DSD: Device-Specific Data
        {
            ToUUID ("daffd814-6eba-4d8c-8a91-bc9bbf4aa301") /* Device
Properties for _DSD */,
            Package (0x03)
            {
                Package (0x02)
                {
                    "compatible",
                    "google,cros-ec-uart"
                },
                ...
            }
        }
    }
```

Since we define our `_HID` as `PRP0001` we need the `of_match_table`
so the ACPI node can bind.