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SubjectRe: [PATCH v2] Documentation: acpi: Add an example for PRP0001
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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@codethink.co.uk>
>> ---
>> 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
>

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