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Date:   Mon, 29 Apr 2019 10:03:36 +0000
From:   Gerald BAEZA <gerald.baeza@...com>
To:     "will.deacon@....com" <will.deacon@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mcoquelin.stm32@...il.com" <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        "corbet@....net" <corbet@....net>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "olof@...om.net" <olof@...om.net>,
        "horms+renesas@...ge.net.au" <horms+renesas@...ge.net.au>,
        "arnd@...db.de" <arnd@...db.de>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        Gerald BAEZA <gerald.baeza@...com>
Subject: [PATCH 1/5] Documentation: perf: stm32: ddrperfm support

The DDRPERFM is the DDR Performance Monitor embedded in STM32MP1 SOC.

This documentation introduces the DDRPERFM, the stm32-ddr-pmu driver
supporting it and how to use it with the perf tool.

Signed-off-by: Gerald Baeza <gerald.baeza@...com>
---
 Documentation/perf/stm32-ddr-pmu.txt | 41 ++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 Documentation/perf/stm32-ddr-pmu.txt

diff --git a/Documentation/perf/stm32-ddr-pmu.txt b/Documentation/perf/stm32-ddr-pmu.txt
new file mode 100644
index 0000000..d5b35b3
--- /dev/null
+++ b/Documentation/perf/stm32-ddr-pmu.txt
@@ -0,0 +1,41 @@
+STM32 DDR Performance Monitor (DDRPERFM)
+========================================
+
+The DDRPERFM is the DDR Performance Monitor embedded in STM32MP1 SOC.
+See STM32MP157 reference manual RM0436 to get a description of this peripheral.
+
+
+The five following counters are supported by stm32-ddr-pmu driver:
+	cnt0: read operations counters		(read_cnt)
+	cnt1: write operations counters		(write_cnt)
+	cnt2: active state counters		(activate_cnt)
+	cnt3: idle state counters		(idle_cnt)
+	tcnt: time count, present for all sets	(time_cnt)
+
+The stm32-ddr-pmu driver relies on the perf PMU framework to expose the
+counters via sysfs:
+	$ ls /sys/bus/event_source/devices/ddrperfm/events
+	activate_cnt  idle_cnt  read_cnt  time_cnt  write_cnt
+
+
+The perf PMU framework is usually invoked via the 'perf stat' tool.
+
+The DDRPERFM is a system monitor that cannot isolate the traffic coming from a
+given thread or CPU, that is why stm32-ddr-pmu driver rejects any 'perf stat'
+call that does not request a system-wide collection: the '-a, --all-cpus'
+option is mandatory!
+
+Example:
+	$ perf stat -e ddrperfm/read_cnt/,ddrperfm/time_cnt/ -a sleep 20
+	Performance counter stats for 'system wide':
+
+	         342541560      ddrperfm/read_cnt/
+	       10660011400      ddrperfm/time_cnt/
+
+	      20.021068551 seconds time elapsed
+
+
+The driver also exposes a 'bandwidth' attribute that can be used to display
+the read/write/total bandwidth achieved during the last 'perf stat' execution.
+	$ cat /sys/bus/event_source/devices/ddrperfm/bandwidth
+	Read = 403, Write = 239, Read & Write = 642 (MB/s)
-- 
2.7.4

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