[RFC PATCH] ARM: dts: meson8b: add reserved memory zones

[Linus Lüssing]

So far, the stress-ng tool for instance quickly resulted in a silent
freeze of the system with no prior notice on a serial console when
running its filesystem or memory stressor classes.

Even with a panic-on-OOM and reboot-on-panic (vm.panic_on_oom=1,
kernel.panic=10) configured, the system would neither reboot nor
would the OOM killer get any chance to otherwise do its job.

By copying the reserved memory sections used for meson8 already,
stress-ng was able to run on an Odroid C1+ just fine for several hours,
the OOM killer was able to do kill processes again and if configured
would successfully trigger a reboot of the system.

Reported-by: Linus Lüssing <linus.luessing at c0d3.blue>

---
The following stress-ng command worked fine now:
$ stress-ng -v --sequential 0 -t 120s --exclude sysfs,opcode --metrics
(5 hours runtime, tested on an Odroid C1+ with an 4.14-rc1 kernel + SMP
+ USB DTS patches)

I do not know why these memory regions would need to be reserved, I
copied them blindly from mesno8.dtsi. Furthermore I'm a little confused
because the Hardkernel sources seem to reserver a totally different
memory region (16MB from the region at 80MB to 96MB):

https://github.com/hardkernel/linux/blob/odroidc-3.10.y/arch/arm/boot/dts/meson8b_odroidc.dts#L58

If anyone more experienced and knowledege in this would like to claim
authorship and responsibility for this patch or would like to suggest
an alternative one then please feel free to do so.
---
 arch/arm/boot/dts/meson8b.dtsi | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/arch/arm/boot/dts/meson8b.dtsi b/arch/arm/boot/dts/meson8b.dtsi
index b9b6600..aa5c79c 100644
--- a/arch/arm/boot/dts/meson8b.dtsi
+++ b/arch/arm/boot/dts/meson8b.dtsi
@@ -92,6 +92,33 @@
 		};
 	};
 
+	reserved-memory {
+		#address-cells = <1>;
+		#size-cells = <1>;
+		ranges;
+
+		/* 2 MiB reserved for Hardware ROM Firmware? */
+		hwrom at 0 {
+			reg = <0x0 0x200000>;
+			no-map;
+		};
+
+		/*
+		 * 1 MiB reserved for the "ARM Power Firmware": this is ARM
+		 * code which is responsible for system suspend. It loads a
+		 * piece of ARC code ("arc_power" in the vendor u-boot tree)
+		 * into SRAM, executes that and shuts down the (last) ARM core.
+		 * The arc_power firmware then checks various wakeup sources
+		 * (IR remote receiver, HDMI CEC, WIFI and Bluetooth wakeup or
+		 * simply the power key) and re-starts the ARM core once it
+		 * detects a wakeup request.
+		 */
+		power-firmware at 4f00000 {
+			reg = <0x4f00000 0x100000>;
+			no-map;
+		};
+	};
+
 	scu at c4300000 {
 		compatible = "arm,cortex-a5-scu";
 		reg = <0xc4300000 0x100>;
-- 
2.1.4