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

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Date:   Mon, 26 Feb 2018 09:54:01 -0600
From:   Samuel Holland <samuel@...lland.org>
To:     Maxime Ripard <maxime.ripard@...tlin.com>,
        Icenowy Zheng <icenowy@...c.io>
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-clk@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH v3 6/7] arm64: allwinner: h6: add the basical Allwinner H6
 DTSI file

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},

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".

Thanks,
Samuel