[PATCH 04/15] ARM: smp_twd: add device tree support

On 01/12/2012 08:36 AM, Marc Zyngier wrote:

Hi Rob,

On 11/01/12 21:05, Rob Herring wrote:

quoted

On 01/11/2012 07:08 AM, Marc Zyngier wrote:

quoted

Add bindings to support DT discovery of the ARM Timer Watchdog
(aka TWD). Only the timer side is converted by this patch.

Cc: Rob Herring <redacted>
Signed-off-by: Marc Zyngier <redacted>
---
 Documentation/devicetree/bindings/arm/twd.txt |   29 +++++++++++
 arch/arm/include/asm/smp_twd.h                |    1 +
 arch/arm/kernel/smp_twd.c                     |   68 ++++++++++++++++++++-----
 3 files changed, 85 insertions(+), 13 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/arm/twd.txt

diff --git a/Documentation/devicetree/bindings/arm/twd.txt b/Documentation/devicetree/bindings/arm/twd.txt
new file mode 100644
index 0000000..a9d5587
--- /dev/null
+++ b/Documentation/devicetree/bindings/arm/twd.txt

@@ -0,0 +1,29 @@
+* ARM Timer Watchdog
+
+ARM 11MP, Cortex-A5 and Cortex-A9 are often associated with a per-core
+Timer-Watchdog (aka TWD), which provides both a per-cpu local timer
+and watchdog.
+
+The TWD is usually attached to a GIC to deliver its two per-processor
+interrupts.
+
+Main node required properties:
+
+- compatible : Should be one of:
+	"arm,cortex-a9-twd"
+	"arm,cortex-a5-twd"
+	"arm,arm11mp-twd"
+	"arm,smp-twd"
+
+- interrupts : Two interrupts to each core, the first one for the
+  timer, the second one for the watchdog.
+
+- reg : Specify the base address and the size of the TWD.
+
+Example:
+
+	twd at 2c000600 {
+		compatible = "arm,arm11mp-twd", "arm,smp-twd";
+		reg = <0x2c000600 0x100>;
+		interrupts = <1 13 0xf01 1 14 0xf01>;
+	};

Why not split the watchdog and timer into 2 nodes? It may not matter
since there is no driver for the timer. If there was, we would have a
problem as you can't match 2 drivers to 1 node.

Don't we hit the opposite problem - two nodes with the same address?

No, because the timer is at 0x600-0x61f and the watchdog is at
0x620-0x63f. There's no DT requirement on address range start or size.

However, the current watchdog driver includes 0x20 in its register
offsets, so changing the base address would require a change to the
driver (but that shouldn't really influence the decision).

Rob