[PATCH v3 13/19] Documentation: perf: stm32: add ddrperfm support

["Clément Le Goffic" <clement.legoffic@foss.st.com>]

The DDRPERFM is the DDR Performance Monitor embedded in STM32MPU 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: Clément Le Goffic <clement.legoffic@foss.st.com>
---
 Documentation/admin-guide/perf/index.rst         |  1 +
 Documentation/admin-guide/perf/stm32-ddr-pmu.rst | 86 ++++++++++++++++++++++++
 2 files changed, 87 insertions(+)

diff --git a/Documentation/admin-guide/perf/index.rst b/Documentation/admin-guide/perf/index.rst
index 072b510385c4..33aedc4ee5c3 100644
--- a/Documentation/admin-guide/perf/index.rst
+++ b/Documentation/admin-guide/perf/index.rst
@@ -29,3 +29,4 @@ Performance monitor support
    cxl
    ampere_cspmu
    mrvl-pem-pmu
+   stm32-ddr-pmu
diff --git a/Documentation/admin-guide/perf/stm32-ddr-pmu.rst b/Documentation/admin-guide/perf/stm32-ddr-pmu.rst
new file mode 100644
index 000000000000..5b02bf44dd7a
--- /dev/null
+++ b/Documentation/admin-guide/perf/stm32-ddr-pmu.rst
@@ -0,0 +1,86 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========================================
+STM32 DDR Performance Monitor (DDRPERFM)
+========================================
+
+The DDRPERFM is the DDR Performance Monitor embedded in STM32MPU SoC.
+The DDR controller provides events to DDRPERFM, once selected they are counted in the DDRPERFM
+peripheral.
+
+In MP1 family, the DDRPERFM is able to count 4 different events at the same time.
+However, the 4 events must belong to the same set.
+One hardware counter is dedicated to the time counter, `time_cnt`.
+
+In MP2 family, the DDRPERFM is able to select between 44 different DDR events.
+As for MP1, there is a dedicated hardware counter for the time.
+It is incremented every 4 DDR clock cycles.
+All the other counters can be freely allocated to count any other DDR event.
+
+The stm32-ddr-pmu driver relies on the perf PMU framework to expose the counters via sysfs:
+
+On MP1:
+
+    .. code-block:: bash
+
+        $ ls /sys/bus/event_source/devices/stm32_ddr_pmu/events/
+        cactive_ddrc                 perf_lpr_req_with_no_credit  perf_op_is_wr
+        ctl_idle                     perf_lpr_xact_when_critical  perf_selfresh_mode
+        dfi_lp_req                   perf_op_is_activate          perf_wr_xact_when_critical
+        dfi_lp_req_cpy               perf_op_is_enter_powerdown   time_cnt
+        perf_hpr_req_with_no_credit  perf_op_is_rd
+        perf_hpr_xact_when_critical  perf_op_is_refresh
+
+On MP2:
+
+    .. code-block:: bash
+
+        $ ls /sys/bus/event_source/devices/stm32_ddr_pmu/events/
+        dfi_is_act       perf_hpr_req_with_nocredit   perf_op_is_spec_ref
+        dfi_is_mpc       perf_hpr_xact_when_critical  perf_op_is_wr
+        dfi_is_mrr       perf_lpr_req_with_nocredit   perf_op_is_zqcal
+        dfi_is_mrw       perf_lpr_xact_when_critical  perf_rank
+        dfi_is_mwr       perf_op_is_act               perf_raw_hazard
+        dfi_is_mwra      perf_op_is_crit_ref          perf_rdwr_transitions
+        dfi_is_preab     perf_op_is_enter_powdn       perf_read_bypass
+        dfi_is_prepb     perf_op_is_enter_selfref     perf_war_hazard
+        dfi_is_rd        perf_op_is_mwr               perf_waw_hazard
+        dfi_is_rda       perf_op_is_pre               perf_window_limit_reached_rd
+        dfi_is_refab     perf_op_is_pre_for_others    perf_window_limit_reached_wr
+        dfi_is_refpb     perf_op_is_pre_for_rdwr      perf_wr_xact_when_critical
+        dfi_is_wr        perf_op_is_rd                time_cnt
+        dfi_is_wra       perf_op_is_rd_activate
+        perf_act_bypass  perf_op_is_ref
+
+
+The perf PMU framework is usually invoked via the 'perf stat' tool.
+
+
+Example:
+
+    .. code-block:: bash
+
+        $ perf stat --timeout 60000 -e stm32_ddr_pmu/dfi_is_act/,\
+        > stm32_ddr_pmu/dfi_is_rd/,\
+        > stm32_ddr_pmu/dfi_is_wr/,\
+        > stm32_ddr_pmu/dfi_is_refab/,\
+        > stm32_ddr_pmu/dfi_is_mrw/,\
+        > stm32_ddr_pmu/dfi_is_rda/,\
+        > stm32_ddr_pmu/dfi_is_wra/,\
+        > stm32_ddr_pmu/dfi_is_mrr/,\
+        > stm32_ddr_pmu/time_cnt/ \
+        > -a sleep 5
+
+         Performance counter stats for 'system wide':
+
+                    481025      stm32_ddr_pmu/dfi_is_act/
+                    732166      stm32_ddr_pmu/dfi_is_rd/
+                    144926      stm32_ddr_pmu/dfi_is_wr/
+                    644154      stm32_ddr_pmu/dfi_is_refab/
+                         0      stm32_ddr_pmu/dfi_is_mrw/
+                         0      stm32_ddr_pmu/dfi_is_rda/
+                         0      stm32_ddr_pmu/dfi_is_wra/
+                         0      stm32_ddr_pmu/dfi_is_mrr/
+                 752347686      stm32_ddr_pmu/time_cnt/
+
+               5.014910750 seconds time elapsed

-- 
2.43.0