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    SubjectRe: [Linaro-acpi] [PATCH v5 18/18] Documentation: ACPI for ARM64
    On Tue, Jan 06, 2015 at 01:59:27PM +0000, Arnd Bergmann wrote:
    > On Tuesday 06 January 2015 11:20:01 Catalin Marinas wrote:
    > > On Mon, Jan 05, 2015 at 08:16:30PM +0000, Arnd Bergmann wrote:
    > > > On Monday 05 January 2015 13:13:02 Catalin Marinas wrote:
    > > > > > since passing no DT tables to OS but
    > > > > > acpi=force is missing is a corner case, we can do a follow up patch to
    > > > > > fix that, does it make sense?
    > > > >
    > > > > Not entirely. Why would no dtb and no acpi=force be a corner case? I
    > > > > thought this should be the default when only ACPI tables are passed, no
    > > > > need for an additional acpi=force argument.
    > > >
    > > > We don't really support the case of only ACPI tables for now. The expectation
    > > > is that you always have working DT support, at least for the next few years
    > > > as ACPI features are ramping up, and without acpi=force it should not try
    > > > to use ACPI at all.
    > >
    > > So if both DT and ACPI are present, just use DT unless acpi=force is
    > > passed. So far I think we agree but what I want to avoid is always
    > > mandating acpi=force even when the DT tables are missing (in the long
    > > run).
    > >
    > > Now, what's preventing a vendor firmware from providing only ACPI
    > > tables? Do we enforce it in some way (arm-acpi.txt, kernel warning etc.)
    > > that both DT and ACPI are supported, or at least that dts files are
    > > merged in the kernel first?
    >
    > We have no way of enforcing what a board vendor ships, so if they want
    > to have ACPI-only machines for MS Windows, they just won't work by
    > default on Linux.

    What do you mean by "won't work by default on Linux"? Assuming no
    additional drivers are needed (i.e. a few devices mentioned in SBSA and
    the rest on a PCIe bus, using existing drivers without further
    modifications), do you still want mainline to fail to boot on such
    ACPI-only systems?

    > Once ACPI support is mature enough, we can also have a whitelist or a
    > different default for using it automatically when no DT is present.

    Having a white-list requires some for of SoC identification. Does ACPI
    provide such thing (like "model" or "compatible" strings in the top DT
    node)?

    > For drivers merged upstream, I would insist that every driver merged
    > for an ARM64 platform has a documented DT binding that is used in the
    > driver.

    That's fine by me. I just hope that for hardware aimed at ACPI we won't
    need many non-PCIe drivers.

    --
    Catalin


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