linux-kernel - [PATCH] arm64: dts: broadcom: bcmbca: bcm4908: Reserve CFE stub area

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Message-ID: <20241003213007.1339811-1-CFSworks@gmail.com>
Date: Thu,  3 Oct 2024 14:30:07 -0700
From: Sam Edwards <cfsworks@...il.com>
To: Florian Fainelli <florian.fainelli@...adcom.com>,
	Rafał Miłecki <rafal@...ecki.pl>,
	William Zhang <william.zhang@...adcom.com>,
	Anand Gore <anand.gore@...adcom.com>,
	Kursad Oney <kursad.oney@...adcom.com>
Cc: Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
	devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Sam Edwards <CFSworks@...il.com>
Subject: [PATCH] arm64: dts: broadcom: bcmbca: bcm4908: Reserve CFE stub area

The CFE bootloader places a stub program at 0x0000-0xFFFF to hold the
secondary CPUs until the boot CPU writes the release address. If Linux
overwrites this program before execution reaches smp_prepare_cpus(), the
secondary CPUs may become inaccessible.

This is only a problem with CFE, and then only until the secondary CPUs
are brought online. However, since it is such a small amount of memory,
it is easiest to reserve it unconditionally.

Therefore, add a /reserved-memory node to bcm4908.dtsi to protect this
critical memory region.

Signed-off-by: Sam Edwards <CFSworks@...il.com>
---
 arch/arm64/boot/dts/broadcom/bcmbca/bcm4908.dtsi | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/arm64/boot/dts/broadcom/bcmbca/bcm4908.dtsi b/arch/arm64/boot/dts/broadcom/bcmbca/bcm4908.dtsi
index 8b924812322c..326f84f746cb 100644
--- a/arch/arm64/boot/dts/broadcom/bcmbca/bcm4908.dtsi
+++ b/arch/arm64/boot/dts/broadcom/bcmbca/bcm4908.dtsi
@@ -68,6 +68,16 @@ l2: l2-cache0 {
 		};
 	};
 
+	reserved-memory {
+		#address-cells = <2>;
+		#size-cells = <2>;
+		ranges;
+
+		cfe-stub@0 {
+			reg = <0 0 0 0x10000>;
+		};
+	};
+
 	axi@...00000 {
 		compatible = "simple-bus";
 		#address-cells = <1>;
-- 
2.44.2