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Date:   Thu, 4 Feb 2021 11:34:46 -0700
From:   Mathieu Poirier <mathieu.poirier@linaro.org>
To:     Suzuki K Poulose <suzuki.poulose@arm.com>
Cc:     Anshuman Khandual <anshuman.khandual@arm.com>,
        linux-arm-kernel@lists.infradead.org, coresight@lists.linaro.org,
        mike.leach@linaro.org, lcherian@marvell.com,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH V3 08/14] coresight: core: Add support for dedicated
 percpu sinks
Message-ID: <20210204183446.GA1636242@xps15>
References: <1611737738-1493-1-git-send-email-anshuman.khandual@arm.com>
 <1611737738-1493-9-git-send-email-anshuman.khandual@arm.com>
 <dce24164-d35b-d9d9-2fcd-e50a1bac0b38@arm.com>
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In-Reply-To: <dce24164-d35b-d9d9-2fcd-e50a1bac0b38@arm.com>
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On Thu, Jan 28, 2021 at 09:16:34AM +0000, Suzuki K Poulose wrote:
> On 1/27/21 8:55 AM, Anshuman Khandual wrote:
> > Add support for dedicated sinks that are bound to individual CPUs. (e.g,
> > TRBE). To allow quicker access to the sink for a given CPU bound source,
> > keep a percpu array of the sink devices. Also, add support for building
> > a path to the CPU local sink from the ETM.
> > 
> > This adds a new percpu sink type CORESIGHT_DEV_SUBTYPE_SINK_PERCPU_SYSMEM.
> > This new sink type is exclusively available and can only work with percpu
> > source type device CORESIGHT_DEV_SUBTYPE_SOURCE_PERCPU_PROC.
> > 
> > This defines a percpu structure that accommodates a single coresight_device
> > which can be used to store an initialized instance from a sink driver. As
> > these sinks are exclusively linked and dependent on corresponding percpu
> > sources devices, they should also be the default sink device during a perf
> > session.
> > 
> > Outwards device connections are scanned while establishing paths between a
> > source and a sink device. But such connections are not present for certain
> > percpu source and sink devices which are exclusively linked and dependent.
> > Build the path directly and skip connection scanning for such devices.
> > 
> > Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> > Cc: Mike Leach <mike.leach@linaro.org>
> > Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> > ---
> > Changes in V3:
> > 
> > - Updated coresight_find_default_sink()
> > 
> >   drivers/hwtracing/coresight/coresight-core.c | 16 ++++++++++++++--
> >   include/linux/coresight.h                    | 12 ++++++++++++
> >   2 files changed, 26 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> > index 0062c89..4795e28 100644
> > --- a/drivers/hwtracing/coresight/coresight-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-core.c
> > @@ -23,6 +23,7 @@
> >   #include "coresight-priv.h"
> >   static DEFINE_MUTEX(coresight_mutex);
> > +DEFINE_PER_CPU(struct coresight_device *, csdev_sink);
> >   /**
> >    * struct coresight_node - elements of a path, from source to sink
> > @@ -784,6 +785,13 @@ static int _coresight_build_path(struct coresight_device *csdev,
> >   	if (csdev == sink)
> >   		goto out;
> > +	if (coresight_is_percpu_source(csdev) && coresight_is_percpu_sink(sink) &&
> > +	    sink == per_cpu(csdev_sink, source_ops(csdev)->cpu_id(csdev))) {
> > +		_coresight_build_path(sink, sink, path);

The return value for _coresight_build_path() needs to be checked.  Otherwise a
failure to allocate a node for the sink will go unoticed and make for a very
hard problem to debug.

> > +		found = true;
> > +		goto out;
> > +	}
> > +
> >   	/* Not a sink - recursively explore each port found on this element */
> >   	for (i = 0; i < csdev->pdata->nr_outport; i++) {
> >   		struct coresight_device *child_dev;
> > @@ -999,8 +1007,12 @@ coresight_find_default_sink(struct coresight_device *csdev)
> >   	int depth = 0;
> >   	/* look for a default sink if we have not found for this device */
> > -	if (!csdev->def_sink)
> > -		csdev->def_sink = coresight_find_sink(csdev, &depth);
> > +	if (!csdev->def_sink) {
> > +		if (coresight_is_percpu_source(csdev))
> > +			csdev->def_sink = per_cpu(csdev_sink, source_ops(csdev)->cpu_id(csdev));
> > +		if (!csdev->def_sink)
> > +			csdev->def_sink = coresight_find_sink(csdev, &depth);
> > +	}
> >   	return csdev->def_sink;
> >   }
> > diff --git a/include/linux/coresight.h b/include/linux/coresight.h
> > index 976ec26..bc3a5ca 100644
> > --- a/include/linux/coresight.h
> > +++ b/include/linux/coresight.h
> > @@ -50,6 +50,7 @@ enum coresight_dev_subtype_sink {
> >   	CORESIGHT_DEV_SUBTYPE_SINK_PORT,
> >   	CORESIGHT_DEV_SUBTYPE_SINK_BUFFER,
> >   	CORESIGHT_DEV_SUBTYPE_SINK_SYSMEM,
> > +	CORESIGHT_DEV_SUBTYPE_SINK_PERCPU_SYSMEM,

Do we absolutely need to add a new sink type?  It is only used in
_coresight_build_path() and that code could be: 

	if (coresight_is_percpu_source(csdev)) {
	    sink == per_cpu(csdev_sink, source_ops(csdev)->cpu_id(csdev));
            if (sink && sink == csdev) {
		_coresight_build_path(sink, sink, path);

> >   };
> >   enum coresight_dev_subtype_link {
> > @@ -428,6 +429,17 @@ static inline void csdev_access_write64(struct csdev_access *csa, u64 val, u32 o
> >   		csa->write(val, offset, false, true);
> >   }
> > +static inline bool coresight_is_percpu_source(struct coresight_device *csdev)
> > +{
> > +	return csdev && (csdev->type == CORESIGHT_DEV_TYPE_SOURCE) &&
> > +	       csdev->subtype.source_subtype == CORESIGHT_DEV_SUBTYPE_SOURCE_PROC;
> 
> Please add () around the last line. Same below.
> 
> > +}
> > +
> > +static inline bool coresight_is_percpu_sink(struct coresight_device *csdev)
> > +{
> > +	return csdev && (csdev->type == CORESIGHT_DEV_TYPE_SINK) &&
> > +	       csdev->subtype.sink_subtype == CORESIGHT_DEV_SUBTYPE_SINK_PERCPU_SYSMEM;
> > +}
> >   #else	/* !CONFIG_64BIT */
> >   static inline u64 csdev_access_relaxed_read64(struct csdev_access *csa,
> > 
> 
> With the above :
> 
> Tested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>