linux-kernel - [PATCH 5/5] arm64: dts: mediatek: mt8195: Set DSU PMU status to fail

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Date:   Tue, 03 Oct 2023 13:13:47 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Fabien Parent <fparent@...libre.com>,
        Miles Chen <miles.chen@...iatek.com>,
        Macpaul Lin <macpaul.lin@...iatek.com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Sam Shih <sam.shih@...iatek.com>,
        Frank Wunderlich <frank-w@...lic-files.de>,
        Jieyy Yang <jieyy.yang@...iatek.com>,
        Tinghan Shen <tinghan.shen@...iatek.com>,
        Seiya Wang <seiya.wang@...iatek.com>, soc@...nel.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, devicetree@...r.kernel.org,
        Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>
Subject: [PATCH 5/5] arm64: dts: mediatek: mt8195: Set DSU PMU status to
 fail

From: "Nícolas F. R. A. Prado" <nfraprado@...labora.com>

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>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Link: https://lore.kernel.org/r/20230720200753.322133-1-nfraprado@collabora.com
---
 arch/arm64/boot/dts/mediatek/mt8195.dtsi | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/boot/dts/mediatek/mt8195.dtsi b/arch/arm64/boot/dts/mediatek/mt8195.dtsi
index 4dbbf8fdab75..43011bc41da7 100644
--- a/arch/arm64/boot/dts/mediatek/mt8195.dtsi
+++ b/arch/arm64/boot/dts/mediatek/mt8195.dtsi
@@ -313,6 +313,7 @@ dsu-pmu {
 		interrupts = <GIC_SPI 18 IRQ_TYPE_LEVEL_HIGH 0>;
 		cpus = <&cpu0>, <&cpu1>, <&cpu2>, <&cpu3>,
 		       <&cpu4>, <&cpu5>, <&cpu6>, <&cpu7>;
+		status = "fail";
 	};
 
 	dmic_codec: dmic-codec {

-- 
2.42.0