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authorJoakim Zhang <qiangqing.zhang@nxp.com>2019-08-28 12:07:56 +0000
committerWill Deacon <will@kernel.org>2019-08-28 14:32:00 +0100
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docs/perf: Add documentation for the i.MX8 DDR PMU
Add some documentation describing the DDR PMU residing in the Freescale i.MDX SoC and its perf driver implementation in Linux. Signed-off-by: Joakim Zhang <qiangqing.zhang@nxp.com> Signed-off-by: Will Deacon <will@kernel.org>
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+=====================================================
+Freescale i.MX8 DDR Performance Monitoring Unit (PMU)
+=====================================================
+
+There are no performance counters inside the DRAM controller, so performance
+signals are brought out to the edge of the controller where a set of 4 x 32 bit
+counters is implemented. This is controlled by the CSV modes programed in counter
+control register which causes a large number of PERF signals to be generated.
+
+Selection of the value for each counter is done via the config registers. There
+is one register for each counter. Counter 0 is special in that it always counts
+“time” and when expired causes a lock on itself and the other counters and an
+interrupt is raised. If any other counter overflows, it continues counting, and
+no interrupt is raised.
+
+The "format" directory describes format of the config (event ID) and config1
+(AXI filtering) fields of the perf_event_attr structure, see /sys/bus/event_source/
+devices/imx8_ddr0/format/. The "events" directory describes the events types
+hardware supported that can be used with perf tool, see /sys/bus/event_source/
+devices/imx8_ddr0/events/.
+ e.g.::
+ perf stat -a -e imx8_ddr0/cycles/ cmd
+ perf stat -a -e imx8_ddr0/read/,imx8_ddr0/write/ cmd
+
+AXI filtering is only used by CSV modes 0x41 (axid-read) and 0x42 (axid-write)
+to count reading or writing matches filter setting. Filter setting is various
+from different DRAM controller implementations, which is distinguished by quirks
+in the driver.
+
+* With DDR_CAP_AXI_ID_FILTER quirk.
+ Filter is defined with two configuration parts:
+ --AXI_ID defines AxID matching value.
+ --AXI_MASKING defines which bits of AxID are meaningful for the matching.
+ 0:corresponding bit is masked.
+ 1: corresponding bit is not masked, i.e. used to do the matching.
+
+ AXI_ID and AXI_MASKING are mapped on DPCR1 register in performance counter.
+ When non-masked bits are matching corresponding AXI_ID bits then counter is
+ incremented. Perf counter is incremented if
+ AxID && AXI_MASKING == AXI_ID && AXI_MASKING
+
+ This filter doesn't support filter different AXI ID for axid-read and axid-write
+ event at the same time as this filter is shared between counters.
+ e.g.::
+ perf stat -a -e imx8_ddr0/axid-read,axi_mask=0xMMMM,axi_id=0xDDDD/ cmd
+ perf stat -a -e imx8_ddr0/axid-write,axi_mask=0xMMMM,axi_id=0xDDDD/ cmd
+
+ NOTE: axi_mask is inverted in userspace(i.e. set bits are bits to mask), and
+ it will be reverted in driver automatically. so that the user can just specify
+ axi_id to monitor a specific id, rather than having to specify axi_mask.
+ e.g.::
+ perf stat -a -e imx8_ddr0/axid-read,axi_id=0x12/ cmd, which will monitor ARID=0x12