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2Freescale i.MX8 DDR Performance Monitoring Unit (PMU)
3=====================================================
4
5There are no performance counters inside the DRAM controller, so performance
6signals are brought out to the edge of the controller where a set of 4 x 32 bit
7counters is implemented. This is controlled by the CSV modes programmed in counter
8control register which causes a large number of PERF signals to be generated.
9
10Selection of the value for each counter is done via the config registers. There
11is one register for each counter. Counter 0 is special in that it always counts
12“time” and when expired causes a lock on itself and the other counters and an
13interrupt is raised. If any other counter overflows, it continues counting, and
14no interrupt is raised.
15
16The "format" directory describes format of the config (event ID) and config1/2
17(AXI filter setting) fields of the perf_event_attr structure, see /sys/bus/event_source/
18devices/imx8_ddr0/format/. The "events" directory describes the events types
19hardware supported that can be used with perf tool, see /sys/bus/event_source/
20devices/imx8_ddr0/events/. The "caps" directory describes filter features implemented
21in DDR PMU, see /sys/bus/events_source/devices/imx8_ddr0/caps/.
22
23    .. code-block:: bash
24
25        perf stat -a -e imx8_ddr0/cycles/ cmd
26        perf stat -a -e imx8_ddr0/read/,imx8_ddr0/write/ cmd
27
28AXI filtering is only used by CSV modes 0x41 (axid-read) and 0x42 (axid-write)
29to count reading or writing matches filter setting. Filter setting is various
30from different DRAM controller implementations, which is distinguished by quirks
31in the driver. You also can dump info from userspace, "caps" directory show the
32type of AXI filter (filter, enhanced_filter and super_filter). Value 0 for
33un-supported, and value 1 for supported.
34
35* With DDR_CAP_AXI_ID_FILTER quirk(filter: 1, enhanced_filter: 0, super_filter: 0).
36  Filter is defined with two configuration parts:
37  --AXI_ID defines AxID matching value.
38  --AXI_MASKING defines which bits of AxID are meaningful for the matching.
39
40      - 0: corresponding bit is masked.
41      - 1: corresponding bit is not masked, i.e. used to do the matching.
42
43  AXI_ID and AXI_MASKING are mapped on DPCR1 register in performance counter.
44  When non-masked bits are matching corresponding AXI_ID bits then counter is
45  incremented. Perf counter is incremented if::
46
47        AxID && AXI_MASKING == AXI_ID && AXI_MASKING
48
49  This filter doesn't support filter different AXI ID for axid-read and axid-write
50  event at the same time as this filter is shared between counters.
51
52  .. code-block:: bash
53
54      perf stat -a -e imx8_ddr0/axid-read,axi_mask=0xMMMM,axi_id=0xDDDD/ cmd
55      perf stat -a -e imx8_ddr0/axid-write,axi_mask=0xMMMM,axi_id=0xDDDD/ cmd
56
57  .. note::
58
59      axi_mask is inverted in userspace(i.e. set bits are bits to mask), and
60      it will be reverted in driver automatically. so that the user can just specify
61      axi_id to monitor a specific id, rather than having to specify axi_mask.
62
63  .. code-block:: bash
64
65        perf stat -a -e imx8_ddr0/axid-read,axi_id=0x12/ cmd, which will monitor ARID=0x12
66
67* With DDR_CAP_AXI_ID_FILTER_ENHANCED quirk(filter: 1, enhanced_filter: 1, super_filter: 0).
68  This is an extension to the DDR_CAP_AXI_ID_FILTER quirk which permits
69  counting the number of bytes (as opposed to the number of bursts) from DDR
70  read and write transactions concurrently with another set of data counters.
71
72* With DDR_CAP_AXI_ID_PORT_CHANNEL_FILTER quirk(filter: 0, enhanced_filter: 0, super_filter: 1).
73  There is a limitation in previous AXI filter, it cannot filter different IDs
74  at the same time as the filter is shared between counters. This quirk is the
75  extension of AXI ID filter. One improvement is that counter 1-3 has their own
76  filter, means that it supports concurrently filter various IDs. Another
77  improvement is that counter 1-3 supports AXI PORT and CHANNEL selection. Support
78  selecting address channel or data channel.
79
80  Filter is defined with 2 configuration registers per counter 1-3.
81  --Counter N MASK COMP register - including AXI_ID and AXI_MASKING.
82  --Counter N MUX CNTL register - including AXI CHANNEL and AXI PORT.
83
84      - 0: address channel
85      - 1: data channel
86
87  PMU in DDR subsystem, only one single port0 exists, so axi_port is reserved
88  which should be 0.
89
90  .. code-block:: bash
91
92      perf stat -a -e imx8_ddr0/axid-read,axi_mask=0xMMMM,axi_id=0xDDDD,axi_channel=0xH/ cmd
93      perf stat -a -e imx8_ddr0/axid-write,axi_mask=0xMMMM,axi_id=0xDDDD,axi_channel=0xH/ cmd
94
95  .. note::
96
97      axi_channel is inverted in userspace, and it will be reverted in driver
98      automatically. So that users do not need specify axi_channel if want to
99      monitor data channel from DDR transactions, since data channel is more
100      meaningful.
101