[PATCH v3 0/3] Add support to configure Coresight Dummy subunit

[PATCH v3 0/3] Add support to configure Coresight Dummy subunit

[Hao Zhang]

Introduction of Coresight Dummy subunit
The Coresight Dummy subunit is for Coresight Dummy component, there are
some specific Coresight devices that HLOS don't have permission to access.
Such as some TPDMs, they would be configured in NON-HLOS side, but it's
necessary to build Coresight path for it to debug. So there need driver
to register dummy devices as Coresight devices.

Commit link:
https://git.codelinaro.org/clo/linux-kernel/coresight/-/tree/coresight-dummy-v3

changes in V3:
1. Use API "dev_dbg" to replace "dev_info". -- Suzuki K Poulose
2. Drop "qcom" property and take it as a dummy framework.
-- Suzuki K Poulose
3. Add new sub-type "CORESIGHT_DEV_SUBTYPE_SINK_DUMMY" to support
coresight dummy module -- Mike Leach
4. Use compatibles "arm,coresight-dummy-source" and
"arm,coresight-dummy-sink" to replace property "qcom,dummy-source" and
"qcom,dummy-sink". -- Mike Leach
5. Define source_devs and sink_devs DEVLIST to replace dummy_devs, make
it clear at the first level. -- Mike Leach
6. Modify subject of YAML patch, drop "YAML schema". -- Krzysztof Kozlowski
7. Drop some redundant items and correct syntax errors in yaml file.
-- Krzysztof Kozlowski/Rob Herring
8. Correct required property of yaml file, constrain out ports to
dummy-source and in ports to dummy-sink. -- Mike Leach
9. Drop "Sysfs files and directories" contents of coresight-dummy.rst.
-- Suzuki K Poulose/Greg Kroah-Hartman
10.Correct syntax errors of coresight-dummy.rst. -- Bagas Sanjaya

Changes in V2:
1. Declare dummy_init and dummy_exit as static to fix missing-prototypes
warnings. -- kernel test robot
2. Fix the errors of coresight-dummy yaml file. -- Rob Herring

Hao Zhang (3):
  Coresight: Add coresight dummy driver
  dt-bindings: arm: Add Coresight Dummy Trace
  Documentation: trace: Add documentation for Coresight Dummy Trace

 .../bindings/arm/arm,coresight-dummy.yaml     | 101 ++++++++++
 .../trace/coresight/coresight-dummy.rst       |  34 ++++
 drivers/hwtracing/coresight/Kconfig           |  11 ++
 drivers/hwtracing/coresight/Makefile          |   1 +
 drivers/hwtracing/coresight/coresight-dummy.c | 179 ++++++++++++++++++
 include/linux/coresight.h                     |   1 +
 6 files changed, 327 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml
 create mode 100644 Documentation/trace/coresight/coresight-dummy.rst
 create mode 100644 drivers/hwtracing/coresight/coresight-dummy.c

-- 
2.17.1

[PATCH v3 1/3] Coresight: Add coresight dummy driver

[Hao Zhang]

Some Coresight devices that kernel don't have permission to access or
configure. So there need driver to register dummy devices as Coresight
devices. It may also be used to define components that may not have
any programming interfaces (e.g, static links), so that paths can be
established in the driver. Provide Coresight API for dummy device
operations, such as enabling and disabling dummy devices. Build the
Coresight path for dummy sink or dummy source for debugging.

Signed-off-by: Hao Zhang <quic_hazha@quicinc.com>
---
 drivers/hwtracing/coresight/Kconfig           |  11 ++
 drivers/hwtracing/coresight/Makefile          |   1 +
 drivers/hwtracing/coresight/coresight-dummy.c | 179 ++++++++++++++++++
 include/linux/coresight.h                     |   1 +
 4 files changed, 192 insertions(+)
 create mode 100644 drivers/hwtracing/coresight/coresight-dummy.c

diff --git a/drivers/hwtracing/coresight/Kconfig b/drivers/hwtracing/coresight/Kconfig
index 2b5bbfffbc4f..06f0a7594169 100644
--- a/drivers/hwtracing/coresight/Kconfig
+++ b/drivers/hwtracing/coresight/Kconfig
@@ -236,4 +236,15 @@ config CORESIGHT_TPDA
 
 	  To compile this driver as a module, choose M here: the module will be
 	  called coresight-tpda.
+
+config CORESIGHT_DUMMY
+	tristate "Dummy driver support"
+	help
+	  Enables support for dummy driver. Dummy driver can be used for
+	  CoreSight sources/sinks that are owned and configured by some
+	  other subsystem and use Linux drivers to configure rest of trace
+	  path.
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called coresight-dummy.
 endif
diff --git a/drivers/hwtracing/coresight/Makefile b/drivers/hwtracing/coresight/Makefile
index 33bcc3f7b8ae..995d3b2c76df 100644
--- a/drivers/hwtracing/coresight/Makefile
+++ b/drivers/hwtracing/coresight/Makefile
@@ -30,3 +30,4 @@ obj-$(CONFIG_CORESIGHT_TPDA) += coresight-tpda.o
 coresight-cti-y := coresight-cti-core.o	coresight-cti-platform.o \
 		   coresight-cti-sysfs.o
 obj-$(CONFIG_ULTRASOC_SMB) += ultrasoc-smb.o
+obj-$(CONFIG_CORESIGHT_DUMMY) += coresight-dummy.o
diff --git a/drivers/hwtracing/coresight/coresight-dummy.c b/drivers/hwtracing/coresight/coresight-dummy.c
new file mode 100644
index 000000000000..1fb8b3d1c170
--- /dev/null
+++ b/drivers/hwtracing/coresight/coresight-dummy.c
@@ -0,0 +1,179 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2023 Qualcomm Innovation Center, Inc. All rights reserved.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/coresight.h>
+#include <linux/of.h>
+#include <linux/pm_runtime.h>
+
+#include "coresight-priv.h"
+#include "coresight-trace-id.h"
+
+struct dummy_drvdata {
+	struct device			*dev;
+	struct coresight_device		*csdev;
+	int				traceid;
+};
+
+DEFINE_CORESIGHT_DEVLIST(source_devs, "dummy_source");
+DEFINE_CORESIGHT_DEVLIST(sink_devs, "dummy_sink");
+
+static int dummy_source_enable(struct coresight_device *csdev,
+			       struct perf_event *event, u32 mode)
+{
+	struct dummy_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
+
+	dev_dbg(drvdata->dev, "Dummy source enabled\n");
+
+	return 0;
+}
+
+static void dummy_source_disable(struct coresight_device *csdev,
+				 struct perf_event *event)
+{
+	struct dummy_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
+
+	dev_dbg(drvdata->dev, "Dummy source disabled\n");
+}
+
+static int dummy_sink_enable(struct coresight_device *csdev, u32 mode,
+				void *data)
+{
+	struct dummy_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
+
+	dev_dbg(drvdata->dev, "Dummy sink enabled\n");
+
+	return 0;
+}
+
+static int dummy_sink_disable(struct coresight_device *csdev)
+{
+	struct dummy_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
+
+	dev_dbg(drvdata->dev, "Dummy sink disabled\n");
+
+	return 0;
+}
+
+static const struct coresight_ops_source dummy_source_ops = {
+	.enable	= dummy_source_enable,
+	.disable = dummy_source_disable,
+};
+
+static const struct coresight_ops dummy_source_cs_ops = {
+	.source_ops = &dummy_source_ops,
+};
+
+static const struct coresight_ops_sink dummy_sink_ops = {
+	.enable	= dummy_sink_enable,
+	.disable = dummy_sink_disable,
+};
+
+static const struct coresight_ops dummy_sink_cs_ops = {
+	.sink_ops = &dummy_sink_ops,
+};
+
+static int dummy_probe(struct platform_device *pdev)
+{
+	int trace_id;
+	struct device *dev = &pdev->dev;
+	struct device_node *node = dev->of_node;
+	struct coresight_platform_data *pdata;
+	struct dummy_drvdata *drvdata;
+	struct coresight_desc desc = { 0 };
+
+	if (of_device_is_compatible(node, "arm,coresight-dummy-source")) {
+		trace_id = coresight_trace_id_get_system_id();
+		if (trace_id < 0)
+			return trace_id;
+
+		desc.name = coresight_alloc_device_name(&source_devs, dev);
+		if (!desc.name)
+			return -ENOMEM;
+
+		desc.type = CORESIGHT_DEV_TYPE_SOURCE;
+		desc.subtype.source_subtype =
+					CORESIGHT_DEV_SUBTYPE_SOURCE_OTHERS;
+		desc.ops = &dummy_source_cs_ops;
+	} else if (of_device_is_compatible(node, "arm,coresight-dummy-sink")) {
+		desc.name = coresight_alloc_device_name(&sink_devs, dev);
+		if (!desc.name)
+			return -ENOMEM;
+
+		desc.type = CORESIGHT_DEV_TYPE_SINK;
+		desc.subtype.sink_subtype = CORESIGHT_DEV_SUBTYPE_SINK_DUMMY;
+		desc.ops = &dummy_sink_cs_ops;
+	} else {
+		dev_err(dev, "Device type not set\n");
+		return -EINVAL;
+	}
+
+	pdata = coresight_get_platform_data(dev);
+	if (IS_ERR(pdata))
+		return PTR_ERR(pdata);
+	pdev->dev.platform_data = pdata;
+
+	drvdata = devm_kzalloc(dev, sizeof(*drvdata), GFP_KERNEL);
+	if (!drvdata)
+		return -ENOMEM;
+
+	drvdata->dev = &pdev->dev;
+	platform_set_drvdata(pdev, drvdata);
+
+	desc.pdata = pdev->dev.platform_data;
+	desc.dev = &pdev->dev;
+	drvdata->csdev = coresight_register(&desc);
+	if (IS_ERR(drvdata->csdev))
+		return PTR_ERR(drvdata->csdev);
+
+	drvdata->traceid = (u8)trace_id;
+
+	pm_runtime_enable(dev);
+	dev_dbg(dev, "Dummy device initialized\n");
+
+	return 0;
+}
+
+static int dummy_remove(struct platform_device *pdev)
+{
+	struct dummy_drvdata *drvdata = platform_get_drvdata(pdev);
+	struct device *dev = &pdev->dev;
+
+	pm_runtime_disable(dev);
+	coresight_unregister(drvdata->csdev);
+	return 0;
+}
+
+static const struct of_device_id dummy_match[] = {
+	{.compatible = "arm,coresight-dummy-source"},
+	{.compatible = "arm,coresight-dummy-sink"},
+	{},
+};
+
+static struct platform_driver dummy_driver = {
+	.probe	= dummy_probe,
+	.remove	= dummy_remove,
+	.driver	= {
+		.name   = "coresight-dummy",
+		.of_match_table = dummy_match,
+	},
+};
+
+static int __init dummy_init(void)
+{
+	return platform_driver_register(&dummy_driver);
+}
+module_init(dummy_init);
+
+static void __exit dummy_exit(void)
+{
+	platform_driver_unregister(&dummy_driver);
+}
+module_exit(dummy_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("CoreSight dummy driver");
diff --git a/include/linux/coresight.h b/include/linux/coresight.h
index f19a47b9bb5a..6db4b49751cf 100644
--- a/include/linux/coresight.h
+++ b/include/linux/coresight.h
@@ -45,6 +45,7 @@ enum coresight_dev_type {
 };
 
 enum coresight_dev_subtype_sink {
+	CORESIGHT_DEV_SUBTYPE_SINK_DUMMY,
 	CORESIGHT_DEV_SUBTYPE_SINK_PORT,
 	CORESIGHT_DEV_SUBTYPE_SINK_BUFFER,
 	CORESIGHT_DEV_SUBTYPE_SINK_SYSMEM,
-- 
2.17.1

[PATCH v3 2/3] dt-bindings: arm: Add Coresight Dummy Trace

[Hao Zhang]

Add new coresight-dummy.yaml file describing the bindings required
to define coresight dummy trace in the device trees.

Signed-off-by: Hao Zhang <quic_hazha@quicinc.com>
---
 .../bindings/arm/arm,coresight-dummy.yaml     | 101 ++++++++++++++++++
 1 file changed, 101 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml

diff --git a/Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml b/Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml
new file mode 100644
index 000000000000..48d864aefaaa
--- /dev/null
+++ b/Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml
@@ -0,0 +1,101 @@
+# SPDX-License-Identifier: GPL-2.0-only or BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/arm/arm,coresight-dummy.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: ARM Coresight Dummy component
+
+description: |
+  Coresight Dummy Trace Module is for the specific devices that kernel
+  don't have permission to access or configure, e.g., CoreSight TPDMs
+  on Qualcomm platforms. So there need driver to register dummy devices
+  as Coresight devices. It may also be used to define components that
+  may not have any programming interfaces (e.g, static links), so that
+  paths can be established in the driver. Provide Coresight API for
+  dummy device operations, such as enabling and disabling dummy devices.
+  Build the Coresight path for dummy sink or dummy source for debugging.
+
+  The primary use case of the coresight dummy is to build path in kernel
+  side for dummy sink and dummy source.
+
+maintainers:
+  - Mao Jinlong <quic_jinlmao@quicinc.com>
+  - Tao Zhang <quic_taozha@quicinc.com>
+  - Hao Zhang <quic_hazha@quicinc.com>
+
+properties:
+  compatible:
+    oneOf:
+      - enum:
+          - arm,coresight-dummy-sink
+          - arm,coresight-dummy-source
+
+  out-ports:
+    $ref: /schemas/graph.yaml#/properties/ports
+
+    properties:
+      port:
+        description: Output connection from the source to Coresight
+          Trace bus.
+        $ref: /schemas/graph.yaml#/properties/port
+
+  in-ports:
+    $ref: /schemas/graph.yaml#/properties/ports
+
+    properties:
+      port:
+        description: Input connection from the Coresight Trace bus to
+          dummy sink, such as Embedded USB debugger(EUD).
+        $ref: /schemas/graph.yaml#/properties/port
+
+required:
+  - compatible
+
+if:
+  # If the compatible contains the below value
+  properties:
+    compatible:
+      contains:
+        const: arm,coresight-dummy-sink
+
+then:
+  required:
+    - in-ports
+
+else:
+  required:
+    - out-ports
+
+additionalProperties: false
+
+examples:
+  # Minimum dummy sink definition. Dummy sink connect to coresight replicator.
+  - |
+    sink {
+      compatible = "arm,coresight-dummy-sink";
+
+      in-ports {
+        port {
+          eud_in_replicator_swao: endpoint {
+            remote-endpoint = <&replicator_swao_out_eud>;
+          };
+        };
+      };
+    };
+
+  # Minimum dummy source definition. Dummy source connect to coresight funnel.
+  - |
+    source {
+      compatible = "arm,coresight-dummy-source";
+
+      out-ports {
+        port {
+          dummy_riscv_out_funnel_swao: endpoint {
+            remote-endpoint = <&funnel_swao_in_dummy_riscv>;
+          };
+        };
+      };
+    };
+
+...
-- 
2.17.1

[PATCH v3 3/3] Documentation: trace: Add documentation for Coresight Dummy Trace

[Hao Zhang]

Add documentation for Coresight Dummy Trace under trace/coresight.

Signed-off-by: Hao Zhang <quic_hazha@quicinc.com>
---
 .../trace/coresight/coresight-dummy.rst       | 34 +++++++++++++++++++
 1 file changed, 34 insertions(+)
 create mode 100644 Documentation/trace/coresight/coresight-dummy.rst

diff --git a/Documentation/trace/coresight/coresight-dummy.rst b/Documentation/trace/coresight/coresight-dummy.rst
new file mode 100644
index 000000000000..d0f73253f694
--- /dev/null
+++ b/Documentation/trace/coresight/coresight-dummy.rst
@@ -0,0 +1,34 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=============================
+Coresight Dummy Trace Module
+=============================
+
+    :Author:   Hao Zhang <quic_hazha@quicinc.com>
+    :Date:     April 2023
+
+Introduction
+---------------------------
+
+Coresight Dummy Trace Module is for the specific devices that kernel
+don't have permission to access or configure, e.g., CoreSight TPDMs
+on Qualcomm platforms. So there need driver to register dummy devices
+as Coresight devices. It may also be used to define components that
+may not have any programming interfaces (e.g, static links), so that
+paths can be established in the driver. Provide Coresight API for
+dummy device operations, such as enabling and disabling dummy devices.
+Build the Coresight path for dummy sink or dummy source for debugging.
+
+Config details
+---------------------------
+
+There are two types of nodes, dummy sink and dummy source. The nodes
+should be observed at the below coresight path::
+
+    ``/sys/bus/coresight/devices``.
+
+e.g.::
+
+    / $ ls -l /sys/bus/coresight/devices | grep dummy
+    dummy0 -> ../../../devices/platform/soc@0/soc@0:dummy_source/dummy0
+    dummy1 -> ../../../devices/platform/soc@0/soc@0:dummy_sink/dummy1
-- 
2.17.1

Re: [PATCH v3 1/3] Coresight: Add coresight dummy driver

[Suzuki K Poulose]

On 22/04/2023 08:37, Hao Zhang wrote:
> Some Coresight devices that kernel don't have permission to access or
> configure. So there need driver to register dummy devices as Coresight
> devices. It may also be used to define components that may not have
> any programming interfaces (e.g, static links), so that paths can be
> established in the driver. Provide Coresight API for dummy device
> operations, such as enabling and disabling dummy devices. Build the
> Coresight path for dummy sink or dummy source for debugging.
> 
> Signed-off-by: Hao Zhang <quic_hazha@quicinc.com>
> ---
>   drivers/hwtracing/coresight/Kconfig           |  11 ++
>   drivers/hwtracing/coresight/Makefile          |   1 +
>   drivers/hwtracing/coresight/coresight-dummy.c | 179 ++++++++++++++++++
>   include/linux/coresight.h                     |   1 +
>   4 files changed, 192 insertions(+)
>   create mode 100644 drivers/hwtracing/coresight/coresight-dummy.c
> 
> diff --git a/drivers/hwtracing/coresight/Kconfig b/drivers/hwtracing/coresight/Kconfig
> index 2b5bbfffbc4f..06f0a7594169 100644
> --- a/drivers/hwtracing/coresight/Kconfig
> +++ b/drivers/hwtracing/coresight/Kconfig
> @@ -236,4 +236,15 @@ config CORESIGHT_TPDA
>   
>   	  To compile this driver as a module, choose M here: the module will be
>   	  called coresight-tpda.
> +
> +config CORESIGHT_DUMMY
> +	tristate "Dummy driver support"
> +	help
> +	  Enables support for dummy driver. Dummy driver can be used for
> +	  CoreSight sources/sinks that are owned and configured by some
> +	  other subsystem and use Linux drivers to configure rest of trace
> +	  path.
> +
> +	  To compile this driver as a module, choose M here: the module will be
> +	  called coresight-dummy.
>   endif
> diff --git a/drivers/hwtracing/coresight/Makefile b/drivers/hwtracing/coresight/Makefile
> index 33bcc3f7b8ae..995d3b2c76df 100644
> --- a/drivers/hwtracing/coresight/Makefile
> +++ b/drivers/hwtracing/coresight/Makefile
> @@ -30,3 +30,4 @@ obj-$(CONFIG_CORESIGHT_TPDA) += coresight-tpda.o
>   coresight-cti-y := coresight-cti-core.o	coresight-cti-platform.o \
>   		   coresight-cti-sysfs.o
>   obj-$(CONFIG_ULTRASOC_SMB) += ultrasoc-smb.o
> +obj-$(CONFIG_CORESIGHT_DUMMY) += coresight-dummy.o
> diff --git a/drivers/hwtracing/coresight/coresight-dummy.c b/drivers/hwtracing/coresight/coresight-dummy.c
> new file mode 100644
> index 000000000000..1fb8b3d1c170
> --- /dev/null
> +++ b/drivers/hwtracing/coresight/coresight-dummy.c
> @@ -0,0 +1,179 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2023 Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/platform_device.h>
> +#include <linux/coresight.h>
> +#include <linux/of.h>
> +#include <linux/pm_runtime.h>
> +
> +#include "coresight-priv.h"
> +#include "coresight-trace-id.h"
> +
> +struct dummy_drvdata {
> +	struct device			*dev;
> +	struct coresight_device		*csdev;
> +	int				traceid;
> +};
> +
> +DEFINE_CORESIGHT_DEVLIST(source_devs, "dummy_source");
> +DEFINE_CORESIGHT_DEVLIST(sink_devs, "dummy_sink");
> +
> +static int dummy_source_enable(struct coresight_device *csdev,
> +			       struct perf_event *event, u32 mode)
> +{
> +	struct dummy_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> +
> +	dev_dbg(drvdata->dev, "Dummy source enabled\n");
> +
> +	return 0;
> +}
> +
> +static void dummy_source_disable(struct coresight_device *csdev,
> +				 struct perf_event *event)
> +{
> +	struct dummy_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> +
> +	dev_dbg(drvdata->dev, "Dummy source disabled\n");
> +}
> +
> +static int dummy_sink_enable(struct coresight_device *csdev, u32 mode,
> +				void *data)
> +{
> +	struct dummy_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> +
> +	dev_dbg(drvdata->dev, "Dummy sink enabled\n");
> +
> +	return 0;
> +}
> +
> +static int dummy_sink_disable(struct coresight_device *csdev)
> +{
> +	struct dummy_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> +
> +	dev_dbg(drvdata->dev, "Dummy sink disabled\n");
> +
> +	return 0;
> +}
> +
> +static const struct coresight_ops_source dummy_source_ops = {
> +	.enable	= dummy_source_enable,
> +	.disable = dummy_source_disable,
> +};
> +
> +static const struct coresight_ops dummy_source_cs_ops = {
> +	.source_ops = &dummy_source_ops,
> +};
> +
> +static const struct coresight_ops_sink dummy_sink_ops = {
> +	.enable	= dummy_sink_enable,
> +	.disable = dummy_sink_disable,
> +};
> +
> +static const struct coresight_ops dummy_sink_cs_ops = {
> +	.sink_ops = &dummy_sink_ops,
> +};
> +
> +static int dummy_probe(struct platform_device *pdev)
> +{
> +	int trace_id;
> +	struct device *dev = &pdev->dev;
> +	struct device_node *node = dev->of_node;
> +	struct coresight_platform_data *pdata;
> +	struct dummy_drvdata *drvdata;
> +	struct coresight_desc desc = { 0 };
> +
> +	if (of_device_is_compatible(node, "arm,coresight-dummy-source")) {
> +		trace_id = coresight_trace_id_get_system_id();

Why is this needed ? If at all we need something, this must be
explicitly asked for. How is this used ?


> +		if (trace_id < 0)
> +			return trace_id;
> +
> +		desc.name = coresight_alloc_device_name(&source_devs, dev);
> +		if (!desc.name)
> +			return -ENOMEM;
> +
> +		desc.type = CORESIGHT_DEV_TYPE_SOURCE;
> +		desc.subtype.source_subtype =
> +					CORESIGHT_DEV_SUBTYPE_SOURCE_OTHERS;
> +		desc.ops = &dummy_source_cs_ops;
> +	} else if (of_device_is_compatible(node, "arm,coresight-dummy-sink")) {
> +		desc.name = coresight_alloc_device_name(&sink_devs, dev);
> +		if (!desc.name)
> +			return -ENOMEM;
> +
> +		desc.type = CORESIGHT_DEV_TYPE_SINK;
> +		desc.subtype.sink_subtype = CORESIGHT_DEV_SUBTYPE_SINK_DUMMY;
> +		desc.ops = &dummy_sink_cs_ops;
> +	} else {
> +		dev_err(dev, "Device type not set\n");
> +		return -EINVAL;
> +	}
> +
> +	pdata = coresight_get_platform_data(dev);
> +	if (IS_ERR(pdata))
> +		return PTR_ERR(pdata);
> +	pdev->dev.platform_data = pdata;
> +
> +	drvdata = devm_kzalloc(dev, sizeof(*drvdata), GFP_KERNEL);
> +	if (!drvdata)
> +		return -ENOMEM;

If we have allocated a traceid, we must clean it up here and/or at 
device removal.

> +
> +	drvdata->dev = &pdev->dev;
> +	platform_set_drvdata(pdev, drvdata);
> +
> +	desc.pdata = pdev->dev.platform_data;
> +	desc.dev = &pdev->dev;
> +	drvdata->csdev = coresight_register(&desc);
> +	if (IS_ERR(drvdata->csdev))
> +		return PTR_ERR(drvdata->csdev);
> +
> +	drvdata->traceid = (u8)trace_id;

Where/how is this used ?

Suzuki

Re: [PATCH v3 2/3] dt-bindings: arm: Add Coresight Dummy Trace

[Rob Herring]

On Sat, Apr 22, 2023 at 03:37:13PM +0800, Hao Zhang wrote:
> Add new coresight-dummy.yaml file describing the bindings required
> to define coresight dummy trace in the device trees.
> 
> Signed-off-by: Hao Zhang <quic_hazha@quicinc.com>
> ---
>  .../bindings/arm/arm,coresight-dummy.yaml     | 101 ++++++++++++++++++
>  1 file changed, 101 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml
> 
> diff --git a/Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml b/Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml
> new file mode 100644
> index 000000000000..48d864aefaaa
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml
> @@ -0,0 +1,101 @@
> +# SPDX-License-Identifier: GPL-2.0-only or BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/arm/arm,coresight-dummy.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: ARM Coresight Dummy component
> +
> +description: |
> +  Coresight Dummy Trace Module is for the specific devices that kernel
> +  don't have permission to access or configure, e.g., CoreSight TPDMs
> +  on Qualcomm platforms. So there need driver to register dummy devices
> +  as Coresight devices. It may also be used to define components that
> +  may not have any programming interfaces (e.g, static links), so that
> +  paths can be established in the driver. Provide Coresight API for
> +  dummy device operations, such as enabling and disabling dummy devices.
> +  Build the Coresight path for dummy sink or dummy source for debugging.
> +
> +  The primary use case of the coresight dummy is to build path in kernel
> +  side for dummy sink and dummy source.

I could imagine the OS wanting to know more information than just 
'dummy'. Is data from an unknown source useful? Likewise, don't you want 
to know where you are sending data too?

> +
> +maintainers:
> +  - Mao Jinlong <quic_jinlmao@quicinc.com>
> +  - Tao Zhang <quic_taozha@quicinc.com>
> +  - Hao Zhang <quic_hazha@quicinc.com>
> +
> +properties:
> +  compatible:
> +    oneOf:
> +      - enum:

Don't need oneOf as there is only one entry.

> +          - arm,coresight-dummy-sink
> +          - arm,coresight-dummy-source
> +
> +  out-ports:
> +    $ref: /schemas/graph.yaml#/properties/ports
> +
> +    properties:
> +      port:
> +        description: Output connection from the source to Coresight
> +          Trace bus.
> +        $ref: /schemas/graph.yaml#/properties/port
> +
> +  in-ports:
> +    $ref: /schemas/graph.yaml#/properties/ports
> +
> +    properties:
> +      port:
> +        description: Input connection from the Coresight Trace bus to
> +          dummy sink, such as Embedded USB debugger(EUD).
> +        $ref: /schemas/graph.yaml#/properties/port
> +
> +required:
> +  - compatible
> +
> +if:
> +  # If the compatible contains the below value
> +  properties:
> +    compatible:
> +      contains:
> +        const: arm,coresight-dummy-sink
> +
> +then:
> +  required:
> +    - in-ports
> +
> +else:
> +  required:
> +    - out-ports

This still allows the nodes when they don't make sense. I think this 
needs to be 2 schema files. The only common part is 'compatible' and 
that's not even shared.

Rob

Re: [PATCH v3 1/3] Coresight: Add coresight dummy driver

[Hao Zhang]

Hi Suzuki,

On 4/24/2023 8:09 PM, Suzuki K Poulose wrote:
> On 22/04/2023 08:37, Hao Zhang wrote:
>> Some Coresight devices that kernel don't have permission to access or
>> configure. So there need driver to register dummy devices as Coresight
>> devices. It may also be used to define components that may not have
>> any programming interfaces (e.g, static links), so that paths can be
>> established in the driver. Provide Coresight API for dummy device
>> operations, such as enabling and disabling dummy devices. Build the
>> Coresight path for dummy sink or dummy source for debugging.
>>
>> Signed-off-by: Hao Zhang <quic_hazha@quicinc.com>
>> ---
>>   drivers/hwtracing/coresight/Kconfig           |  11 ++
>>   drivers/hwtracing/coresight/Makefile          |   1 +
>>   drivers/hwtracing/coresight/coresight-dummy.c | 179 ++++++++++++++++++
>>   include/linux/coresight.h                     |   1 +
>>   4 files changed, 192 insertions(+)
>>   create mode 100644 drivers/hwtracing/coresight/coresight-dummy.c
>>
>> diff --git a/drivers/hwtracing/coresight/Kconfig 
>> b/drivers/hwtracing/coresight/Kconfig
>> index 2b5bbfffbc4f..06f0a7594169 100644
>> --- a/drivers/hwtracing/coresight/Kconfig
>> +++ b/drivers/hwtracing/coresight/Kconfig
>> @@ -236,4 +236,15 @@ config CORESIGHT_TPDA
>>         To compile this driver as a module, choose M here: the module 
>> will be
>>         called coresight-tpda.
>> +
>> +config CORESIGHT_DUMMY
>> +    tristate "Dummy driver support"
>> +    help
>> +      Enables support for dummy driver. Dummy driver can be used for
>> +      CoreSight sources/sinks that are owned and configured by some
>> +      other subsystem and use Linux drivers to configure rest of trace
>> +      path.
>> +
>> +      To compile this driver as a module, choose M here: the module 
>> will be
>> +      called coresight-dummy.
>>   endif
>> diff --git a/drivers/hwtracing/coresight/Makefile 
>> b/drivers/hwtracing/coresight/Makefile
>> index 33bcc3f7b8ae..995d3b2c76df 100644
>> --- a/drivers/hwtracing/coresight/Makefile
>> +++ b/drivers/hwtracing/coresight/Makefile
>> @@ -30,3 +30,4 @@ obj-$(CONFIG_CORESIGHT_TPDA) += coresight-tpda.o
>>   coresight-cti-y := coresight-cti-core.o    coresight-cti-platform.o \
>>              coresight-cti-sysfs.o
>>   obj-$(CONFIG_ULTRASOC_SMB) += ultrasoc-smb.o
>> +obj-$(CONFIG_CORESIGHT_DUMMY) += coresight-dummy.o
>> diff --git a/drivers/hwtracing/coresight/coresight-dummy.c 
>> b/drivers/hwtracing/coresight/coresight-dummy.c
>> new file mode 100644
>> index 000000000000..1fb8b3d1c170
>> --- /dev/null
>> +++ b/drivers/hwtracing/coresight/coresight-dummy.c
>> @@ -0,0 +1,179 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/*
>> + * Copyright (c) 2023 Qualcomm Innovation Center, Inc. All rights 
>> reserved.
>> + */
>> +
>> +#include <linux/kernel.h>
>> +#include <linux/module.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/coresight.h>
>> +#include <linux/of.h>
>> +#include <linux/pm_runtime.h>
>> +
>> +#include "coresight-priv.h"
>> +#include "coresight-trace-id.h"
>> +
>> +struct dummy_drvdata {
>> +    struct device            *dev;
>> +    struct coresight_device        *csdev;
>> +    int                traceid;
>> +};
>> +
>> +DEFINE_CORESIGHT_DEVLIST(source_devs, "dummy_source");
>> +DEFINE_CORESIGHT_DEVLIST(sink_devs, "dummy_sink");
>> +
>> +static int dummy_source_enable(struct coresight_device *csdev,
>> +                   struct perf_event *event, u32 mode)
>> +{
>> +    struct dummy_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>> +
>> +    dev_dbg(drvdata->dev, "Dummy source enabled\n");
>> +
>> +    return 0;
>> +}
>> +
>> +static void dummy_source_disable(struct coresight_device *csdev,
>> +                 struct perf_event *event)
>> +{
>> +    struct dummy_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>> +
>> +    dev_dbg(drvdata->dev, "Dummy source disabled\n");
>> +}
>> +
>> +static int dummy_sink_enable(struct coresight_device *csdev, u32 mode,
>> +                void *data)
>> +{
>> +    struct dummy_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>> +
>> +    dev_dbg(drvdata->dev, "Dummy sink enabled\n");
>> +
>> +    return 0;
>> +}
>> +
>> +static int dummy_sink_disable(struct coresight_device *csdev)
>> +{
>> +    struct dummy_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>> +
>> +    dev_dbg(drvdata->dev, "Dummy sink disabled\n");
>> +
>> +    return 0;
>> +}
>> +
>> +static const struct coresight_ops_source dummy_source_ops = {
>> +    .enable    = dummy_source_enable,
>> +    .disable = dummy_source_disable,
>> +};
>> +
>> +static const struct coresight_ops dummy_source_cs_ops = {
>> +    .source_ops = &dummy_source_ops,
>> +};
>> +
>> +static const struct coresight_ops_sink dummy_sink_ops = {
>> +    .enable    = dummy_sink_enable,
>> +    .disable = dummy_sink_disable,
>> +};
>> +
>> +static const struct coresight_ops dummy_sink_cs_ops = {
>> +    .sink_ops = &dummy_sink_ops,
>> +};
>> +
>> +static int dummy_probe(struct platform_device *pdev)
>> +{
>> +    int trace_id;
>> +    struct device *dev = &pdev->dev;
>> +    struct device_node *node = dev->of_node;
>> +    struct coresight_platform_data *pdata;
>> +    struct dummy_drvdata *drvdata;
>> +    struct coresight_desc desc = { 0 };
>> +
>> +    if (of_device_is_compatible(node, "arm,coresight-dummy-source")) {
>> +        trace_id = coresight_trace_id_get_system_id();
> 
> Why is this needed ? If at all we need something, this must be
> explicitly asked for. How is this used ?
>  >
>> +        if (trace_id < 0)
>> +            return trace_id;
>> +
>> +        desc.name = coresight_alloc_device_name(&source_devs, dev);
>> +        if (!desc.name)
>> +            return -ENOMEM;
>> +
>> +        desc.type = CORESIGHT_DEV_TYPE_SOURCE;
>> +        desc.subtype.source_subtype =
>> +                    CORESIGHT_DEV_SUBTYPE_SOURCE_OTHERS;
>> +        desc.ops = &dummy_source_cs_ops;
>> +    } else if (of_device_is_compatible(node, 
>> "arm,coresight-dummy-sink")) {
>> +        desc.name = coresight_alloc_device_name(&sink_devs, dev);
>> +        if (!desc.name)
>> +            return -ENOMEM;
>> +
>> +        desc.type = CORESIGHT_DEV_TYPE_SINK;
>> +        desc.subtype.sink_subtype = CORESIGHT_DEV_SUBTYPE_SINK_DUMMY;
>> +        desc.ops = &dummy_sink_cs_ops;
>> +    } else {
>> +        dev_err(dev, "Device type not set\n");
>> +        return -EINVAL;
>> +    }
>> +
>> +    pdata = coresight_get_platform_data(dev);
>> +    if (IS_ERR(pdata))
>> +        return PTR_ERR(pdata);
>> +    pdev->dev.platform_data = pdata;
>> +
>> +    drvdata = devm_kzalloc(dev, sizeof(*drvdata), GFP_KERNEL);
>> +    if (!drvdata)
>> +        return -ENOMEM;
> 
> If we have allocated a traceid, we must clean it up here and/or at 
> device removal.
>  >> +
>> +    drvdata->dev = &pdev->dev;
>> +    platform_set_drvdata(pdev, drvdata);
>> +
>> +    desc.pdata = pdev->dev.platform_data;
>> +    desc.dev = &pdev->dev;
>> +    drvdata->csdev = coresight_register(&desc);
>> +    if (IS_ERR(drvdata->csdev))
>> +        return PTR_ERR(drvdata->csdev);
>> +
>> +    drvdata->traceid = (u8)trace_id;
> 
> Where/how is this used ?
> 
> Suzuki
> 
This is required for ATID filtering funtion which is our HW design for 
ETR, we need to set traceid/atid for etm, stm and tpda. Therefore, it's 
needed if the type of dummy source is etm. This part is waiting for 
upstream. I will remove it now and upstream it as the part of ATID 
filtering in the further.

Thanks,
Hao

Re: [PATCH v3 2/3] dt-bindings: arm: Add Coresight Dummy Trace

[Hao Zhang]

Hi Rob,

On 4/26/2023 2:46 AM, Rob Herring wrote:
> On Sat, Apr 22, 2023 at 03:37:13PM +0800, Hao Zhang wrote:
>> Add new coresight-dummy.yaml file describing the bindings required
>> to define coresight dummy trace in the device trees.
>>
>> Signed-off-by: Hao Zhang <quic_hazha@quicinc.com>
>> ---
>>   .../bindings/arm/arm,coresight-dummy.yaml     | 101 ++++++++++++++++++
>>   1 file changed, 101 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml b/Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml
>> new file mode 100644
>> index 000000000000..48d864aefaaa
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/arm/arm,coresight-dummy.yaml
>> @@ -0,0 +1,101 @@
>> +# SPDX-License-Identifier: GPL-2.0-only or BSD-2-Clause
>> +%YAML 1.2
>> +---
>> +$id: http://devicetree.org/schemas/arm/arm,coresight-dummy.yaml#
>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>> +
>> +title: ARM Coresight Dummy component
>> +
>> +description: |
>> +  Coresight Dummy Trace Module is for the specific devices that kernel
>> +  don't have permission to access or configure, e.g., CoreSight TPDMs
>> +  on Qualcomm platforms. So there need driver to register dummy devices
>> +  as Coresight devices. It may also be used to define components that
>> +  may not have any programming interfaces (e.g, static links), so that
>> +  paths can be established in the driver. Provide Coresight API for
>> +  dummy device operations, such as enabling and disabling dummy devices.
>> +  Build the Coresight path for dummy sink or dummy source for debugging.
>> +
>> +  The primary use case of the coresight dummy is to build path in kernel
>> +  side for dummy sink and dummy source.
> 
> I could imagine the OS wanting to know more information than just
> 'dummy'. Is data from an unknown source useful? Likewise, don't you want
> to know where you are sending data too?
> 
The necessary information for Coresight is connection between different 
components, so there is in-port for dummy sink and out-port for dummy 
source. We can get the whole path from the source to sink in device tree.

>> +
>> +maintainers:
>> +  - Mao Jinlong <quic_jinlmao@quicinc.com>
>> +  - Tao Zhang <quic_taozha@quicinc.com>
>> +  - Hao Zhang <quic_hazha@quicinc.com>
>> +
>> +properties:
>> +  compatible:
>> +    oneOf:
>> +      - enum:
> 
> Don't need oneOf as there is only one entry.
> 
OK, I will remove it in the next version of patch.
>> +          - arm,coresight-dummy-sink
>> +          - arm,coresight-dummy-source
>> +
>> +  out-ports:
>> +    $ref: /schemas/graph.yaml#/properties/ports
>> +
>> +    properties:
>> +      port:
>> +        description: Output connection from the source to Coresight
>> +          Trace bus.
>> +        $ref: /schemas/graph.yaml#/properties/port
>> +
>> +  in-ports:
>> +    $ref: /schemas/graph.yaml#/properties/ports
>> +
>> +    properties:
>> +      port:
>> +        description: Input connection from the Coresight Trace bus to
>> +          dummy sink, such as Embedded USB debugger(EUD).
>> +        $ref: /schemas/graph.yaml#/properties/port
>> +
>> +required:
>> +  - compatible
>> +
>> +if:
>> +  # If the compatible contains the below value
>> +  properties:
>> +    compatible:
>> +      contains:
>> +        const: arm,coresight-dummy-sink
>> +
>> +then:
>> +  required:
>> +    - in-ports
>> +
>> +else:
>> +  required:
>> +    - out-ports
> 
> This still allows the nodes when they don't make sense. I think this
> needs to be 2 schema files. The only common part is 'compatible' and
> that's not even shared.
>  > Rob
Dummy driver is very simple, the only goal of it is to build a path in 
kernel for subsystem, so we want to handle dummy source and sink in a 
generic framework.

Thanks,
Hao

Re: [PATCH v3 3/3] Documentation: trace: Add documentation for Coresight Dummy Trace

[Bagas Sanjaya]

[-- Attachment #1: Type: text/plain, Size: 3536 bytes --]

On Sat, Apr 22, 2023 at 03:37:14PM +0800, Hao Zhang wrote:
> +Introduction
> +---------------------------
> +
> +Coresight Dummy Trace Module is for the specific devices that kernel
> +don't have permission to access or configure, e.g., CoreSight TPDMs
> +on Qualcomm platforms. So there need driver to register dummy devices
> +as Coresight devices. It may also be used to define components that
> +may not have any programming interfaces (e.g, static links), so that
> +paths can be established in the driver. Provide Coresight API for
> +dummy device operations, such as enabling and disabling dummy devices.
> +Build the Coresight path for dummy sink or dummy source for debugging.
> +
> +Config details
> +---------------------------
> +
> +There are two types of nodes, dummy sink and dummy source. The nodes
> +should be observed at the below coresight path::
> +
> +    ``/sys/bus/coresight/devices``.
> +
> +e.g.::
> +
> +    / $ ls -l /sys/bus/coresight/devices | grep dummy
> +    dummy0 -> ../../../devices/platform/soc@0/soc@0:dummy_source/dummy0
> +    dummy1 -> ../../../devices/platform/soc@0/soc@0:dummy_sink/dummy1

The wording confuses me, so I have to make the improv:

---- >8 ----
diff --git a/Documentation/trace/coresight/coresight-dummy.rst b/Documentation/trace/coresight/coresight-dummy.rst
index 7cb59f080c8892..f0a92669288b0c 100644
--- a/Documentation/trace/coresight/coresight-dummy.rst
+++ b/Documentation/trace/coresight/coresight-dummy.rst
@@ -8,27 +8,25 @@ Coresight Dummy Trace Module
     :Date:     May 2023
 
 Introduction
----------------------------
+------------
 
-Coresight Dummy Trace Module is for the specific devices that kernel
-don't have permission to access or configure, e.g., CoreSight TPDMs
-on Qualcomm platforms. So there need driver to register dummy devices
-as Coresight devices. It may also be used to define components that
-may not have any programming interfaces (e.g, static links), so that
-paths can be established in the driver. Provide Coresight API for
-dummy device operations, such as enabling and disabling dummy devices.
-Build the Coresight path for dummy sink or dummy source for debugging.
+The Coresight dummy trace module is for the specific devices that kernel don't
+have permission to access or configure, e.g., CoreSight TPDMs on Qualcomm
+platforms. For these devices, a dummy driver is needed to register them as
+Coresight devices. The module may also be used to define components that may
+not have any programming interfaces (e.g, static links), so that paths can be
+created in the driver. It provides Coresight API for operations on dummy
+devices, such as enabling and disabling them. It also provides the Coresight
+dummy sink/source paths for debugging.
 
 Config details
----------------------------
+--------------
 
-There are two types of nodes, dummy sink and dummy source. The nodes
-should be observed at the below coresight path::
+There are two types of nodes, dummy sink and dummy source. These nodes
+are available at ``/sys/bus/coresight/devices``.
 
-    ``/sys/bus/coresight/devices``.
+Example output::
 
-e.g.::
-
-    / $ ls -l /sys/bus/coresight/devices | grep dummy
+    $ ls -l /sys/bus/coresight/devices | grep dummy
     dummy_sink0 -> ../../../devices/platform/soc@0/soc@0:sink/dummy_sink0
     dummy_source0 -> ../../../devices/platform/soc@0/soc@0:source/dummy_source0

Thanks.

-- 
An old man doll... just what I always wanted! - Clara

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Re: [PATCH v3 3/3] Documentation: trace: Add documentation for Coresight Dummy Trace

[Hao Zhang]

Hi Bagas,

On 5/10/2023 12:29 PM, Bagas Sanjaya wrote:
> On Sat, Apr 22, 2023 at 03:37:14PM +0800, Hao Zhang wrote:
>> +Introduction
>> +---------------------------
>> +
>> +Coresight Dummy Trace Module is for the specific devices that kernel
>> +don't have permission to access or configure, e.g., CoreSight TPDMs
>> +on Qualcomm platforms. So there need driver to register dummy devices
>> +as Coresight devices. It may also be used to define components that
>> +may not have any programming interfaces (e.g, static links), so that
>> +paths can be established in the driver. Provide Coresight API for
>> +dummy device operations, such as enabling and disabling dummy devices.
>> +Build the Coresight path for dummy sink or dummy source for debugging.
>> +
>> +Config details
>> +---------------------------
>> +
>> +There are two types of nodes, dummy sink and dummy source. The nodes
>> +should be observed at the below coresight path::
>> +
>> +    ``/sys/bus/coresight/devices``.
>> +
>> +e.g.::
>> +
>> +    / $ ls -l /sys/bus/coresight/devices | grep dummy
>> +    dummy0 -> ../../../devices/platform/soc@0/soc@0:dummy_source/dummy0
>> +    dummy1 -> ../../../devices/platform/soc@0/soc@0:dummy_sink/dummy1
> 
> The wording confuses me, so I have to make the improv:
> 
> ---- >8 ----
> diff --git a/Documentation/trace/coresight/coresight-dummy.rst b/Documentation/trace/coresight/coresight-dummy.rst
> index 7cb59f080c8892..f0a92669288b0c 100644
> --- a/Documentation/trace/coresight/coresight-dummy.rst
> +++ b/Documentation/trace/coresight/coresight-dummy.rst
> @@ -8,27 +8,25 @@ Coresight Dummy Trace Module
>       :Date:     May 2023
>   
>   Introduction
> ----------------------------
> +------------
>   
> -Coresight Dummy Trace Module is for the specific devices that kernel
> -don't have permission to access or configure, e.g., CoreSight TPDMs
> -on Qualcomm platforms. So there need driver to register dummy devices
> -as Coresight devices. It may also be used to define components that
> -may not have any programming interfaces (e.g, static links), so that
> -paths can be established in the driver. Provide Coresight API for
> -dummy device operations, such as enabling and disabling dummy devices.
> -Build the Coresight path for dummy sink or dummy source for debugging.
> +The Coresight dummy trace module is for the specific devices that kernel don't
> +have permission to access or configure, e.g., CoreSight TPDMs on Qualcomm
> +platforms. For these devices, a dummy driver is needed to register them as
> +Coresight devices. The module may also be used to define components that may
> +not have any programming interfaces (e.g, static links), so that paths can be
> +created in the driver. It provides Coresight API for operations on dummy
> +devices, such as enabling and disabling them. It also provides the Coresight
> +dummy sink/source paths for debugging.
>   
>   Config details
> ----------------------------
> +--------------
>   
> -There are two types of nodes, dummy sink and dummy source. The nodes
> -should be observed at the below coresight path::
> +There are two types of nodes, dummy sink and dummy source. These nodes
> +are available at ``/sys/bus/coresight/devices``.
>   
> -    ``/sys/bus/coresight/devices``.
> +Example output::
>   
> -e.g.::
> -
> -    / $ ls -l /sys/bus/coresight/devices | grep dummy
> +    $ ls -l /sys/bus/coresight/devices | grep dummy
>       dummy_sink0 -> ../../../devices/platform/soc@0/soc@0:sink/dummy_sink0
>       dummy_source0 -> ../../../devices/platform/soc@0/soc@0:source/dummy_source0
> 
> Thanks.
> 

Thanks for your review and comments, will update it in the next patch 
series.

Thanks,
Hao