linux-kernel - Re: [PATCH] arm64: dts: mediatek: mt8195: Set DSU PMU status to fail

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Message-ID: <e053e9fe-5d88-44f1-bb24-280113665185@notapiano>
Date:   Thu, 10 Aug 2023 18:12:14 -0400
From:   Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>
To:     Matthias Brugger <matthias.bgg@...il.com>
Cc:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, kernel@...labora.com,
        Chen-Yu Tsai <wenst@...omium.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Seiya Wang <seiya.wang@...iatek.com>,
        Tinghan Shen <tinghan.shen@...iatek.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH] arm64: dts: mediatek: mt8195: Set DSU PMU status to fail

On Thu, Jul 20, 2023 at 04:07:51PM -0400, Nícolas F. R. A. Prado wrote:
> The DSU PMU allows monitoring performance events in the DSU cluster,
> which is done by configuring and reading back values from the DSU PMU
> system registers. However, for write-access to be allowed by ELs lower
> than EL3, the EL3 firmware needs to update the setting on the ACTLR3_EL3
> register, as it is disallowed by default.
> 
> That configuration is not done on the firmware used by the MT8195 SoC,
> as a consequence, booting a MT8195-based machine like
> mt8195-cherry-tomato-r2 with CONFIG_ARM_DSU_PMU enabled hangs the kernel
> just as it writes to the CLUSTERPMOVSCLR_EL1 register, since the
> instruction faults to EL3, and BL31 apparently just re-runs the
> instruction over and over.
> 
> Mark the DSU PMU node in the Devicetree with status "fail", as the
> machine doesn't have a suitable firmware to make use of it from the
> kernel, and allowing its driver to probe would hang the kernel.
> 
> Fixes: 37f2582883be ("arm64: dts: Add mediatek SoC mt8195 and evaluation board")
> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>

Hi Matthias,

gentle ping on this patch, as it's not possible to boot MT8195 Chromebooks with
the mainline defconfig without this fix.

Thanks,
Nícolas