[PATCH v5 5/8] ARM: dts: Add an armv7 timer for zx297520v3

[Stefan Dösinger]

The stock kernel does not use this timer, but it seems to work fine. The
board has other board-specific timers that would need a driver and I see
no reason to bother with them since the arm standard timer works.

The caveat is the non-standard GIC setup needed to handle the timer's
level-low PPI. This is the responsibility of the boot loader and
documented in Documentation/arch/arm/zte/zx297520v3.rst.

Signed-off-by: Stefan Dösinger <stefandoesinger at gmail.com>
---
 arch/arm/boot/dts/zte/zx297520v3.dtsi | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/arch/arm/boot/dts/zte/zx297520v3.dtsi b/arch/arm/boot/dts/zte/zx297520v3.dtsi
index 0fff00f910d6..903050c684cb 100644
--- a/arch/arm/boot/dts/zte/zx297520v3.dtsi
+++ b/arch/arm/boot/dts/zte/zx297520v3.dtsi
@@ -20,6 +20,21 @@ cpu at 0 {
 		};
 	};
 
+	timer {
+		compatible = "arm,armv7-timer";
+		interrupts = <GIC_PPI 13 IRQ_TYPE_LEVEL_LOW>,
+			     <GIC_PPI 14 IRQ_TYPE_LEVEL_LOW>,
+			     <GIC_PPI 11 IRQ_TYPE_LEVEL_LOW>,
+			     <GIC_PPI 10 IRQ_TYPE_LEVEL_LOW>;
+		clock-frequency = <26000000>;
+		interrupt-parent = <&gic>;
+		/* I don't think uboot sets CNTVOFF and the stock kernel doesn't use the
+		 * arm timer at all. Since this is a single CPU system I don't think it
+		 * really matters that the offset is random though.
+		 */
+		arm,cpu-registers-not-fw-configured;
+	};
+
 	soc {
 		#address-cells = <1>;
 		#size-cells = <1>;
@@ -27,6 +42,15 @@ soc {
 		interrupt-parent = <&gic>;
 		ranges;
 
+		/* The GIC has a non-standard way of configuring ints between level-low/level
+		 * high or rising edge/falling edge at 0xf2202070 and onwards. See AP_INT_MODE_BASE
+		 * and AP_PPI_MODE_REG in the ZTE kernel, although the offsets in the kernel source
+		 * seem wrong.
+		 *
+		 * Everything defaults to active-high/rising edge, but the timer is active-low. We
+		 * currently rely on the boot loader to change timer IRQs to active-low for us for
+		 * now.
+		 */
 		gic: interrupt-controller at f2000000 {
 			compatible = "arm,gic-v3";
 			interrupt-controller;

-- 
2.53.0