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    SubjectRe: [linux-sunxi] Re: [PATCH v3 6/7] arm64: allwinner: h6: add the basical Allwinner H6 DTSI file
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    Hi,

    On 26/02/18 15:54, Samuel Holland wrote:
    > On 02/26/18 03:26, Maxime Ripard wrote:
    >> On Fri, Feb 23, 2018 at 11:22:06PM +0800, Icenowy Zheng wrote:
    >>>>> + psci {
    >>>>> + compatible = "arm,psci-0.2";
    >>>>> + method = "smc";
    >>>>> + };
    >>>>
    >>>> Is it needed? The bootloader should fill it with whatever version it
    >>>> has, shouldn't it?
    >>>
    >>> But we now use ATF rather than U-Boot PSCI. U-Boot will not fill ATF
    >>> info.
    >>>
    >>> See A64/H5 device trees.
    >>
    >> So if the PSCI version implemented in ATF ever changes, we would have
    >> to update all the DT everywhere, but only if you're running the new
    >> version?
    >
    > Yes but no. PSCI 1.0 is generally backward compatible with PSCI 0.2. In fact,
    > the Linux driver treats them exactly the same:
    >
    > { .compatible = "arm,psci-0.2", .data = psci_0_2_init},
    > { .compatible = "arm,psci-1.0", .data = psci_0_2_init},

    Yeah, it's actually unclear why we have that new compatible name in the
    first place, since starting with PSCI v0.2 the version can be perfectly
    read using the mandatory PSCI_VERSION call. And DT aims to only cover
    things that are not discoverable.

    > For the H6, however, the oldest ATF source available (which I believe was the
    > one in use during bringup) is based on mainline 1.4, and is already at PSCI
    > version 1.1:
    >
    > [ 0.000000] psci: probing for conduit method from DT.
    > [ 0.000000] psci: PSCIv1.1 detected in firmware.
    > [ 0.000000] psci: Using standard PSCI v0.2 function IDs
    > [ 0.000000] psci: MIGRATE_INFO_TYPE not supported.
    >
    > So we could go ahead and bump the compatible to "arm,psci-1.0".

    I'd rather leave it at "arm,psci-0.2", since this improves compatibility
    to other OSes or DT users.

    Cheers,
    Andre.

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