Re: [PATCH v2 1/3] Coresight: Add coresight dummy driver

[Mike Leach]

Hi,

A few additional comments....

On Tue, 28 Mar 2023 at 10:24, Hao Zhang <quic_hazha@xxxxxxxxxxx> 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@xxxxxxxxxxx> 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@xxxxxxxxxxx>
> >>>> ---
> >>>>   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?

> >>>> +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.

> >>>> +               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

> >>>> +       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
> >>>>
> >>>
> >>>
> >



-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK