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    SubjectRe: [PATCH v4 00/13] Add ACPI _DSD and unified device properties support
    On Wed, Oct 15, 2014 at 03:46:39PM +0100, Darren Hart wrote:
    >
    >
    > On 10/15/14 16:08, David Woodhouse wrote:
    > >
    > >> We have been checking for all DT platforms, and that's a bug for DT.
    > >> Copying that bug to ACPI is inexcusable given we know it's a bug to do
    > >> so.
    > >
    > > We'll, perhaps it should be named 'used-by-firmware' and actually it's
    > > just as valid under ACPI as it is on RTAS systems. All it does is stop the
    > > OS from using the port.
    > >
    > >> I understand that. However, where a binding doesn't make sense (as in
    > >> this case), it shouldn't be enabled for ACPI as it provides a larger
    > >> surface area for misuse, for no benefit.
    > >
    > > These are *optional* properties. They were optional precisely *because*
    > > they only make sense in some cases. I don't know that it makes sense to
    > > take them away. The benefit we get is *consistency*. For example if
    > > someone *does* use the property in question as 'used-by-firmware' and
    > > expects the OS not to touch it, we don't want that to change behaviour
    > > between ACPI and fdt boots.
    >
    > My comment was going to be along the same lines. It is an optional
    > parameter, which is what I would expect for a firmware-specific type of
    > property.
    >
    > I also don't agree that this is "copying that bug to ACPI". This line of
    > code has no impact to ACPI. No ACPI implementation should add this,
    > certainly not if it was actually tested as it would not run if it was
    > present in the _DSD. So... what's the problem exactly? Or perhaps more
    > specifically:
    >
    > Mark, what would you propose we do differently to enable this driver to
    > be firmware-type agnostic?

    For this particular driver, all I'm asking for is that the
    "used-by-rtas" property is not moved over from of_find_property to
    device_get_property. It is irrelevant for all ACPI systems. Evidently my
    comment was unclear; I apologise for that.

    We have status = "disabled" as a less specific mechanism for telling the
    OS to ignore a node in DT. I was under the impression that ACPI already
    had a mechanism for marking devices to be ignored, but perhaps I am
    mistaken.

    The concerns I mentioned at the end of my original reply were of a more
    general nature than this particular device description.

    Thanks,
    Mark.


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