Re: [PATCH 11/11] dts: bindings: Document device tree binding for Arm TRBE

On 1/3/21 10:35 PM, Rob Herring wrote:

On Wed, Dec 23, 2020 at 03:33:43PM +0530, Anshuman Khandual wrote:

quoted

This patch documents the device tree binding in use for Arm TRBE.

Cc: devicetree@vger.kernel.org
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Leach <redacted>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Anshuman Khandual <redacted>
---
Changes in V1:

- TRBE DT entry has been renamed as 'arm, trace-buffer-extension'

 Documentation/devicetree/bindings/arm/trbe.txt | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/arm/trbe.txt

diff --git a/Documentation/devicetree/bindings/arm/trbe.txt b/Documentation/devicetree/bindings/arm/trbe.txt
new file mode 100644
index 0000000..001945d
--- /dev/null
+++ b/Documentation/devicetree/bindings/arm/trbe.txt

@@ -0,0 +1,20 @@
+* Trace Buffer Extension (TRBE)
+
+Trace Buffer Extension (TRBE) is used for collecting trace data generated
+from a corresponding trace unit (ETE) using an in memory trace buffer.
+
+** TRBE Required properties:
+
+- compatible : should be one of:
+	       "arm,trace-buffer-extension"
+
+- interrupts : Exactly 1 PPI must be listed. For heterogeneous systems where
+	       TRBE is only supported on a subset of the CPUs, please consult
+	       the arm,gic-v3 binding for details on describing a PPI partition.
+
+** Example:
+
+trbe {
+	compatible = "arm,trace-buffer-extension";
+	interrupts = <GIC_PPI 15 IRQ_TYPE_LEVEL_HIGH>;

If only an interrupt, then could just be part of ETE? If not, how is 
this hardware block accessed? An interrupt alone is not enough unless 
there's some architected way to access.

TRBE hardware block is accessed via respective new system registers but the
PPI number where the IRQ will be triggered for various buffer events, would
depend on the platform as defined in the SBSA.

TRBE would need a ETE to work but the reverse is not true. ETE might just
be present without a corresponding TRBE and can work with traditional sinks.
Hence just wondering whether it would be prudent to add the TRBE interrupt
number as part of the ETE DT specification.

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