Re: [PATCH 02/10] dt: add img,axd.txt device tree binding document

From: Qais Yousef
Date: Mon Aug 24 2015 - 09:49:32 EST

On 08/24/2015 02:26 PM, Mark Rutland wrote:
On Mon, Aug 24, 2015 at 01:39:11PM +0100, Qais Yousef wrote:
Signed-off-by: Qais Yousef <qais.yousef@xxxxxxxxxx>
Cc: Rob Herring <robh+dt@xxxxxxxxxx>
Cc: Pawel Moll <pawel.moll@xxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Ian Campbell <ijc+devicetree@xxxxxxxxxxxxxx>
Cc: Kumar Gala <galak@xxxxxxxxxxxxxx>
Cc: devicetree@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
.../devicetree/bindings/sound/img,axd.txt | 34 ++++++++++++++++++++++
1 file changed, 34 insertions(+)
create mode 100644 Documentation/devicetree/bindings/sound/img,axd.txt

diff --git a/Documentation/devicetree/bindings/sound/img,axd.txt b/Documentation/devicetree/bindings/sound/img,axd.txt
new file mode 100644
index 000000000000..6a8764a79d01
--- /dev/null
+++ b/Documentation/devicetree/bindings/sound/img,axd.txt
@@ -0,0 +1,34 @@
+* AXD Audio Processing IP Binding *
+Required properties:
+- compatible: "img,axd"
This sounds awfully generic. Is there not a more complete name?

Shouldn't img prefix to help against this? We can sure use another name though like "img,axd-audio-decoder" or something like that. I'll need to check.

+- clocks: phandle for the clock that drives AXD.
+- interrupts: the GIC interrupt where AXD is connected
+- gic-irq: it takes two non-zero values, the first one is the host hwirq and
+ the second one is AXD's. Host's hwirq should match the value in
+ interrupts.
I don't understand what this gic-irq property is for; and it generally
doesn't look right.

Could you please describe what this is and why you thing it is

AXD and host cores exchange interrupts using GIC interrupt controller. To configure AXD firmware to send and listen to the correct GIC interrupts we need these values, hence this property.

If there's a way to reverse the irq mappings of 'interrupts' property from the driver code we can get rid of that and have 2 interrupts properties instead. But as far as I can see there's no way to get the hw irq value from the mapped linux irq unless I missed something.

+Optional properties:
+- vpe: VPE number on which AXD should start. Must be provided if AXD is
+ running as a single VPE along Linux on the same core.
+ It can't be VPE0.
+ The VPE will be offlined before AXD is loaded.
Likewise could you please elaborate on this is?

What is a VPE number? What does it mean to start at that number?

VPE is MIPS notation of hardware thread. Instead of being a complete separate core AXD can run as a hardware thread (VPE) inside a Linux core. This number indicates which hardware thread to run AXD at.

+- inbuf-size: size of shared input buffers area. By default it's 0x7800 bytes.
+- outbuf-size: size of shared output buffers area. By default it's 0x3c000 bytes.
Is this something the kernel dynamically allocates? Why does this need
to be in the DT?

We use CMA to allocate this buffer area. This optional property is there to give the user a chance to use larger/smaller buffers if they think they need to. This buffer area is shared between Linux and AXD to exchange data.



+ axdclk: axdclk@400M {
+ #clock-cells = <0>;
+ compatible = "fixed-clock";
+ clock-frequency = <400000000>;
+ };
+ axd {
+ compatible = "img,axd";
+ clocks = <&axdclk>;
+ interrupts = <36 IRQ_TYPE_EDGE_RISING>;
+ gic-irq = <36 37>;
+ vpe = <1>;
+ };

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at