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

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Date:   Mon, 25 Mar 2019 17:30:32 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Thomas Preston <thomas.preston@...ethink.co.uk>
Cc:     rjw@...ysocki.net, lenb@...nel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, mika.westerberg@...ux.intel.com
Subject: Re: [PATCH v2] Documentation: acpi: Add an example for PRP0001

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.

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.

> Signed-off-by: Thomas Preston <thomas.preston@...ethink.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

-- 
With Best Regards,
Andy Shevchenko