linux-kernel - [RFC PATCH] arm64: dts: ti: k3-j721s2: Add reserved status in msmc node

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Date: Tue, 16 Apr 2024 15:06:48 +0530
From: Udit Kumar <u-kumar1@...com>
To: <nm@...com>, <vigneshr@...com>, <robh@...nel.org>, <krzk+dt@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <francesco@...cini.it>
CC: <kristo@...nel.org>, <conor+dt@...nel.org>, <linux-kernel@...r.kernel.org>,
        Udit Kumar <u-kumar1@...com>
Subject: [RFC PATCH] arm64: dts: ti: k3-j721s2: Add reserved status in msmc node

TI K3 SOCs have msmc sram, part of it can be configured as L3 cache
depending upon system firmware configuration file.

MSMC memory typically host four tenants atf, system firmware (tifs),
l3 cache and as sram.

Allocation done for atf, tifs and l3-cache is not accessible in address
space of OS.
Therefore u-boot deletes sysfw and l3cache node before passing DT to OS[0].
But keeping tifs (system firmware) subnode as is.

Since TIFS node is not also accessible to OS, I need suggestion for
selection of right option.

In my view we can handle in two ways

1) delete tifs node as well
In this case, only accessible sram will be visible to OS[1]

2) make these nodes (tifs, atf and l3cache) as reserved,
so that OS has complete view of memory.

This is patch for option 2 to mark atf, l3-cache and tifs as
reserved.

Also other options are welcome.

[0]: https://github.com/u-boot/u-boot/blob/master/arch/arm/mach-k3/common_fdt.c#L67
[1]: https://lore.kernel.org/all/20230420081128.3617214-1-u-kumar1@ti.com/

Signed-off-by: Udit Kumar <u-kumar1@...com>
---
 arch/arm64/boot/dts/ti/k3-j721s2-main.dtsi | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/boot/dts/ti/k3-j721s2-main.dtsi b/arch/arm64/boot/dts/ti/k3-j721s2-main.dtsi
index 3cb06a7e4117..f64c8b0780d8 100644
--- a/arch/arm64/boot/dts/ti/k3-j721s2-main.dtsi
+++ b/arch/arm64/boot/dts/ti/k3-j721s2-main.dtsi
@@ -25,14 +25,17 @@ msmc_ram: sram@...00000 {
 		ranges = <0x0 0x0 0x70000000 0x400000>;

 		atf-sram@0 {
+			status = "reserved";
 			reg = <0x0 0x20000>;
 		};

 		tifs-sram@...000 {
+			status = "reserved";
 			reg = <0x1f0000 0x10000>;
 		};

 		l3cache-sram@...000 {
+			status = "reserved";
 			reg = <0x200000 0x200000>;
 		};
 	};
-- 
2.34.1