linux-kernel - Re: [PATCH v7 4/4] arm64: dts: Add Caninos Loucos Labrador v3

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Message-ID: <4fc1047f-2b14-4430-b9b2-1e682881de0c@castello.eng.br>
Date:   Thu, 15 Oct 2020 20:57:01 -0300
From:   Matheus Castello <matheus@...tello.eng.br>
To:     Catalin Marinas <catalin.marinas@....com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Olof Johansson <olof@...om.net>,
        Andreas Färber <afaerber@...e.de>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>, edgar.righi@...tec.org.br,
        igor.lima@...tec.org.br, Helen Koike <helen.koike@...labora.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        DTML <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-actions@...ts.infradead.org, Will Deacon <will@...nel.org>
Subject: Re: [PATCH v7 4/4] arm64: dts: Add Caninos Loucos Labrador v3


Em 9/22/20 7:26 AM, Catalin Marinas escreveu:
> On Tue, Sep 22, 2020 at 10:32:06AM +0200, Arnd Bergmann wrote:
>> On Tue, Sep 22, 2020 at 8:15 AM Manivannan Sadhasivam
>> <manivannan.sadhasivam@...aro.org> wrote:
>>> On Mon, Sep 21, 2020 at 11:43:02PM -0300, Matheus Castello wrote:
>>>> +     /* Labrador v3 firmware does not support PSCI */
>>>
>>> Oops. This is unfortunate... I'm not sure if this is even acceptable for
>>> ARM64 machines.
>>>
>>> Let me add Olof and Arnd...
>>
>> Adding Catalin and Will for additional input as well, this is more their
>> area than ours.
>>
>> I don't think we have formalized this as a policy, but we clearly don't
>> want new boards to use the spin table hack. As there are other
>> boards using psci on the same chip, I don't think this is a
>> hardware bug.
> 
> I fully agree, we shouldn't allow new boards to use the spin-table
> method unless EL3 is missing on the CPU implementation (not the case
> here; only the APM hardware has this issue). Unfortunately we missed
> another platform with A53, see commit bc66392d8258 ("arm64: dts: fsl:
> Add device tree for S32V234-EVB").
> 
> The kernel relies on firmware for other things (power management, errata
> workarounds), so an SMC calling convention compliant firmware is highly
> recommended. I also don't see why it would be that hard to add PSCI.
> Even if you don't port something like Trusted Firmware, U-Boot has basic
> support for PSCI.
> 
> So from my perspective, NAK on this patch.
>

Thanks Arnd and Catalin, this is really just a limitation of the 
bootloader developed by manufactures that comes embedded in the board. I 
will drop this in the next version.

> I'm tempted to also modify smp_spin_table_cpu_init() to print a big
> warning and return an error if this is attempted on new platforms. IOW,
> we make it a policy from now on.
>