Re: [RFC] ACPI table HID/CID allocation

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On 21 November 2017 at 09:19, Udit Kumar <udit.kumar@nxp.com> wrote:
> Hi,
>
> I am enabling ACPI on NXP platform , In order to do minimal changes in Linux
> driver for device-driver binding.
>
> I want to use PRP0001 device as CID and HID as actual (NXP allocated HID).
>
> So that Linux can bind with PRP0001 and  compatible field, where as other OS
> (Window etc) can rely on HID.
>
> Below is sample, ACPI table for SPI controller and its slave device.
>
>
>
> Hope this approach is ok ?
>

No, it is not.

Architecting an ACPI platform is not a matter of taking a device tree
and converting each node into an ACPI device.

Linux/DT makes no assumptions about the presence of firmware. This
means most device drivers have to manage clocks, regulators etc
because they will not be in a known state. Also, the OS can own all
devices in the system.

Linux/ACPI relies on the firmware to set up clocks and regulators, and
uses abstract firmware methods to manage power states etc. Also, due
to the dependency on UEFI, things like the RTC and NOR flash are not
exposed to the OS via device nodes, but via UEFI runtime services.

In a nutshell, the difference between ACPI and DT is that the handoff
point between the OS and the firmware is at a different abstraction
level.

So no, it is not ok to use PRP0001 + compatible for everything. It may
be acceptable in some exceptional cases, but you will have to explain
why. Everything else should use proper ACPI bindings.

-- 
Ard.