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
