netdev - Re: [PATCH v1 2/3] net/fsl: acpize xgmac

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Date:   Thu, 18 Jun 2020 10:43:24 -0500
From:   Jeremy Linton <jeremy.linton@....com>
To:     Andrew Lunn <andrew@...n.ch>,
        Calvin Johnson <calvin.johnson@....nxp.com>
Cc:     Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Jon <jon@...id-run.com>,
        Cristi Sovaiala <cristian.sovaiala@....com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Madalin Bucur <madalin.bucur@....nxp.com>,
        netdev@...r.kernel.org, linux.cj@...il.com
Subject: Re: [PATCH v1 2/3] net/fsl: acpize xgmac_mdio

Hi,

On 6/17/20 12:34 PM, Andrew Lunn wrote:
> On Wed, Jun 17, 2020 at 10:45:34PM +0530, Calvin Johnson wrote:
>> From: Jeremy Linton <jeremy.linton@....com>
> 
>> +static const struct acpi_device_id xgmac_acpi_match[] = {
>> +	{ "NXP0006", (kernel_ulong_t)NULL },
> 
> Hi Jeremy
> 
> What exactly does NXP0006 represent? An XGMAC MDIO bus master? Some
> NXP MDIO bus master? An XGMAC Ethernet controller which has an NXP
> MDIO bus master? A cluster of Ethernet controllers?

Strictly speaking its a NXP defined (they own the "NXP" prefix per 
https://uefi.org/pnp_id_list) id. So, they have tied it to a specific 
bit of hardware. In this case it appears to be a shared MDIO master 
which isn't directly contained in an Ethernet controller. Its somewhat 
similar to a  "nxp,xxxxx" compatible id, depending on how they are using 
it to identify an ACPI device object (_HID()/_CID()).

So AFAIK, this is all valid ACPI usage as long as the ID maps to a 
unique device/object.

> 
> Is this documented somewhere? In the DT world we have a clear
> documentation for all the compatible strings. Is there anything
> similar in the ACPI world for these magic numbers?

Sadly not fully. The mentioned PNP and ACPI 
(https://uefi.org/acpi_id_list) ids lists are requested and registered 
to a given organization. But, once the prefix is owned, it becomes the 
responsibility of that organization to assign & manage the ID's with 
their prefix. There are various individuals/etc which have collected 
lists, though like PCI ids, there aren't any formal publishing requirements.