Re: [PATCH v2] Documentation: acpi: Add an example for PRP0001

[Thomas Preston]

On 25/03/2019 15:30, Andy Shevchenko wrote:
> On Mon, Mar 25, 2019 at 03:12:10PM +0000, Thomas Preston wrote:
> > Add an example for the magic PRP0001 device ID which allows matching
> > ACPI devices against drivers using OF Device Tree compatible property.
>
> > It wasn't clear to me that PRP0001 could be used in _CID.
>
> Yes, but it's not necessary to have it if we have defined a _HID.
>
> In that case PRP0001 is a temporary stub until corresponding driver
> incorporates an official _HID.
>
> On the contrary, when there is no official _HID available, PRP0001 can be used
> instead directly as a _HID and no _CID is needed.

In that case, how do we uniquely identify devices in sysfs? We have a
case where sound/soc/soc-core.c generates an i2c codec name i2c-TDA7802:00.
It is useful to identify that device by part name, rather than some indexed
generic PRP device i2c-PRP0001:04. I can achieve this with:

	_HID("TDA7802")
	_CID("PRP0001")
	...
	compatible = "st,tda7802" // driver I want to load using OF DT

> I would really recommend to look at the examples in meta-acpi repository. There
> are cases like described above.
>
> This one is good enough, though see below.

I will drop the superfluous _CID - I think the example is still useful
to have. Even if we don't illustrate my special case for _HID/_CID.

> > Signed-off-by: Thomas Preston <thomas.preston@xxxxxxxxxxxxxxx>
> > ---
> >   Documentation/acpi/enumeration.txt | 31 +++++++++++++++++++++++++++++++
> >   1 file changed, 31 insertions(+)
> >
> > diff --git a/Documentation/acpi/enumeration.txt b/Documentation/acpi/enumeration.txt
> > index 7bcf9c3d9fbe..8375fc506b47 100644
> > --- a/Documentation/acpi/enumeration.txt
> > +++ b/Documentation/acpi/enumeration.txt
> > @@ -410,6 +410,37 @@ Specifically, the device IDs returned by _HID and preceding PRP0001 in the _CID
> >   return package will be checked first.  Also in that case the bus type the device
> >   will be enumerated to depends on the device ID returned by _HID.
> >   
> > +For example, the following ACPI sample might be used to enumerate an lm75-type
> > +I2C temperature sensor and match it to the driver using the Device Tree
> > +namespace link:
> > +
> > +	Device (TMP0)
> > +	{
> > +		/* _HID will appear in sysfs */
> > +		Name (_HID, "PRP0001")
> > +
>
> > +		/* _CID can also be used to search for "compatible" property */
> > +		Name (_CID, "PRP0001")
>
> So, these lines are superfluous as stated exaxtly in a following paragraph.
>
> > +
> > +		Name (_DSD, Package() {
> > +			ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> > +			Package () {
> > +				Package (2) { "compatible", "ti,tmp75" },
> > +			}
> > +		})
> > +		Method (_CRS, 0, Serialized)
> > +		{
> > +			Name (SBUF, ResourceTemplate ()
> > +			{
> > +				I2cSerialBusV2 (0x48, ControllerInitiated,
> > +					400000, AddressingMode7Bit,
> > +					"\\_SB.PCI0.I2C1", 0x00,
> > +					ResourceConsumer, , Exclusive,)
> > +			})
> > +			Return (SBUF)
> > +		}
> > +	}
> > +
> >   It is valid to define device objects with a _HID returning PRP0001 and without
> >   the "compatible" property in the _DSD or a _CID as long as one of their
> >   ancestors provides a _DSD with a valid "compatible" property.  Such device