Message-ID: <bab8fc7f-77b3-472f-2d2b-b1275d753888@arm.com>
Date:   Tue, 28 Mar 2023 13:21:20 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Hao Zhang <quic_hazha@...cinc.com>,
        Mike Leach <mike.leach@...aro.org>
Cc:     Mathieu Poirier <mathieu.poirier@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Konrad Dybcio <konradybcio@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jonathan Corbet <corbet@....net>, Leo Yan <leo.yan@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Tingwei Zhang <quic_tingweiz@...cinc.com>,
        Jinlong Mao <quic_jinlmao@...cinc.com>,
        Yuanfang Zhang <quic_yuanfang@...cinc.com>,
        Tao Zhang <quic_taozha@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        linux-arm-msm@...r.kernel.org,
        Bjorn Andersson <andersson@...nel.org>,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v2 1/3] Coresight: Add coresight dummy driver

On 28/03/2023 12:25, Hao Zhang wrote:
> Hi Mike,
> 
> On 3/28/2023 6:06 PM, Mike Leach wrote:
>> Hi,
>>
>> A few additional comments....
>>
>> On Tue, 28 Mar 2023 at 10:24, Hao Zhang <quic_hazha@...cinc.com> wrote:
>>>
>>> Hi Suzuki,
>>>
>>> On 3/28/2023 4:35 PM, Suzuki K Poulose wrote:
>>>> On 28/03/2023 08:22, Hao Zhang wrote:
>>>>> Hi Mike,
>>>>>
>>>>> On 3/27/2023 11:58 PM, Mike Leach wrote:
>>>>>> Hi,
>>>>>>
>>>>>> On Fri, 24 Mar 2023 at 06:16, Hao Zhang <quic_hazha@...cinc.com> 
>>>>>> wrote:
>>>>>>>
>>>>>>> Some Coresight devices that HLOS don't have permission to access
>>>>>>> or configure. Such as Coresight sink EUD, some TPDMs etc. So there
>>>>>>> need driver to register dummy devices as Coresight devices. 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@...cinc.com>
>>>>>>> ---
>>>>>>>    drivers/hwtracing/coresight/Kconfig           |  11 ++
>>>>>>>    drivers/hwtracing/coresight/Makefile          |   1 +
>>>>>>>    drivers/hwtracing/coresight/coresight-dummy.c | 176
>>>>>>> ++++++++++++++++++
>>>>>>>    3 files changed, 188 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..2d4eb3e546eb
>>>>>>> --- /dev/null
>>>>>>> +++ b/drivers/hwtracing/coresight/coresight-dummy.c
>>>>>>> @@ -0,0 +1,176 @@
>>>>>>> +// 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(dummy_devs, "dummy");
>>>>>>> +
>>
>> minor nit: can we have dummy_source and dummy_sink as the device names
>> to make it clear at the first level what these are without having to
>> look at the attributes?
>>
> 
> This is a good advice, dummy_source and dummy_sink are two different 
> components, so it's better to separate it at the first level. I will 
> take your advice in the next version of patch.
> 
>>>>>>> +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_info(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_info(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_info(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_info(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_sink dummy_sink_ops = {
>>>>>>> +       .enable         = dummy_sink_enable,
>>>>>>> +       .disable        = dummy_sink_disable,
>>>>>>> +};
>>>>>>> +
>>>>>>> +static const struct coresight_ops dummy_cs_ops = {
>>>>>>> +       .source_ops     = &dummy_source_ops,
>>>>>>> +       .sink_ops       = &dummy_sink_ops,
>>>>>>> +};
>>>>>>> +
>>>>>>> +static int dummy_probe(struct platform_device *pdev)
>>>>>>> +{
>>>>>>> +       int ret, trace_id;
>>>>>>> +       struct device *dev = &pdev->dev;
>>>>>>> +       struct coresight_platform_data *pdata;
>>>>>>> +       struct dummy_drvdata *drvdata;
>>>>>>> +       struct coresight_desc desc = { 0 };
>>>>>>> +
>>>>>>> +       desc.name = coresight_alloc_device_name(&dummy_devs, dev);
>>>>>>> +       if (!desc.name)
>>>>>>> +               return -ENOMEM;
>>>>>>> +
>>>>>>> +       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);
>>>>>>> +
>>>>>>> +       if (of_property_read_bool(pdev->dev.of_node,
>>>>>>> "qcom,dummy-source")) {
>>>>>>> +               desc.type = CORESIGHT_DEV_TYPE_SOURCE;
>>>>>>> +               desc.subtype.source_subtype =
>>>>>>> + CORESIGHT_DEV_SUBTYPE_SOURCE_OTHERS;
>>>>>>> +       } else if (of_property_read_bool(pdev->dev.of_node,
>>>>>>> +                                        "qcom,dummy-sink")) {
>>
>> It would simplify things if the compatibles were
>> arm,coresight-dummy-source and arm,coresight-dummy-sink - and drop the
>> two additional attributes, using of_device_is_compatible() here.
>>
> 
> Yes, I will update it in the next version of patch.
> 
>>>>>>> +               desc.type = CORESIGHT_DEV_TYPE_SINK;
>>>>>>> +               desc.subtype.sink_subtype =
>>>>>>> CORESIGHT_DEV_SUBTYPE_SINK_BUFFER;
>>>>>>
>>>>>> This will break the automatic sink selection on a system where 
>>>>>> perf is
>>>>>> looking for a default sink and the dummy sink is closest  / first
>>>>>> discovered.
>>>>>>
>>>>>> i.e. when perf record -e cs_etm// <options>
>>>>>> is used to trace a program in linux, a dummy sink appearing in the
>>>>>> coresight tree with this designation may be selected.
>>>>>>
>>>>>> This needs to be corrected, probably with a unique sub-type that
>>>>>> appears before the CORESIGHT_DEV_SUBTYPE_SINK_BUFFER value in the 
>>>>>> enum
>>>>>> as the selection is based on >= CORESIGHT_DEV_SUBTYPE_SINK_BUFFER.
>>>>>>
>>>>
>>>> Good point Mike.
>>>>
>>>>>> By implication adding a new value - will possibly affect other code
>>>>>> using the enum values so will need to be checked
>>>>>>
>>>>>> Regards
>>>>>>
>>>>>> Mike
>>>>>>
>>>>>
>>>>> Thanks for your comments, I will add a new sub-type for dummy sink and
>>>>> check the impact of it.
>>>>
>>>> Please keep this as the lowest priority, something like:
>>>>
>>>>    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,
>>>>           CORESIGHT_DEV_SUBTYPE_SINK_PERCPU_SYSMEM,
>>>> };
>>>>
>>>> This should be fine without any impact on the existing code, as we
>>>> expect the driver modules to be updated with the new core module.
>>>>
>>>> Suzuki
>>>>
>>>
>>> Sure, I will take your advice in the next version of patch.
>>>
>>> Thanks,
>>> Hao
>>>
>>>>
>>>>>
>>>>> Thanks,
>>>>> Hao
>>>>>
>>>>>>
>>>>>>> +       } else {
>>>>>>> +               dev_info(dev, "Device type not set\n");
>>>>>>> +               return -EINVAL;
>>>>>>> +       }
>>>>>>> +
>>>>>>> +       desc.ops = &dummy_cs_ops;
>>>>>>> +       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);
>>>>>>> +
>>>>>>> +       trace_id = coresight_trace_id_get_system_id();
>>>>>>> +       if (trace_id < 0) {
>>>>>>> +               ret = trace_id;
>>>>>>> +               goto cs_unregister;
>>>>>>> +       }
>>>>>>> +       drvdata->traceid = (u8)trace_id;
>>>>>>> +
>>
>> Number of issues here:-
>> 1) Why are sinks being given a trace ID? - they do not need them.
>> 2) how is the trace ID communicated to the underlying hardware system?
>> - there appears to be no way of doing this here. Without this you
>> cannot guarantee that there will not be clashes.
>> Although your use case may mitigate against this - for this to be a
>> generic module there must be a way to ensure the IDs can be discovered
>> externally.
>> 3) Trace IDs are a limited resource - most sources allocate on enable,
>> release on disable  / reset - this would be preferable.
>>
>>
>> Regards
>>
>> Mike

Good points Mike.

> 
> 1. It should not be given a trace ID for sink, I will correct it in the 
> next version of patch.
> 2. There are other patches to transmit the trace ID to sub-processor. 
> But We have an upstream dependency on QMI project. We will sync with 
> them for the other related patches.
> 3. The trace ID of dummy source need to be communicated to the 
> sub-processor, it's better to be allocated on probe, that would reduce 
> communications costs. On the other hand, there will be few dummy 
> sources. I'd perfer to allocate it on probe function.

Could that be delayed to dynamic allocation when the device is enabled ?
Also, do we need a property for the dummy-source to "allocate" a
traceID?

i.e., add a "property" (not compatible) 
"arm,coresight-dummy-source-traceid" ?

Suzuki


> 
> Thanks,
> Hao
> 
>>
>>>>>>> +       pm_runtime_enable(dev);
>>>>>>> +       dev_info(dev, "Dummy device initialized\n");
>>>>>>> +
>>>>>>> +       return 0;
>>>>>>> +
>>>>>>> +cs_unregister:
>>>>>>> +       coresight_unregister(drvdata->csdev);
>>>>>>> +
>>>>>>> +       return ret;
>>>>>>> +}
>>>>>>> +
>>>>>>> +static int dummy_remove(struct platform_device *pdev)
>>>>>>> +{
>>>>>>> +       struct dummy_drvdata *drvdata = platform_get_drvdata(pdev);
>>>>>>> +       struct device *dev = &pdev->dev;
>>>>>>> +
>>>>>>> +       coresight_trace_id_put_system_id(drvdata->traceid);
>>>>>>> +       pm_runtime_disable(dev);
>>>>>>> +       coresight_unregister(drvdata->csdev);
>>>>>>> +       return 0;
>>>>>>> +}
>>>>>>> +
>>>>>>> +static const struct of_device_id dummy_match[] = {
>>>>>>> +       {.compatible = "qcom,coresight-dummy"},
>>>>>>> +       {},
>>>>>>> +};
>>>>>>> +
>>>>>>> +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 source driver");
>>>>>>> -- 
>>>>>>> 2.17.1
>>>>>>>
>>>>>>
>>>>>>
>>>>
>>
>>
>>

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