perf/amd/ibs: Fix ->config to sample period calculation for OP PMU

Instead of using standard perf_event_attr->freq=0 and ->sample_period
fields, IBS event in 'sample period mode' can also be opened by setting
period value directly in perf_event_attr->config in a MaxCnt bit-field
format.

IBS OP MaxCnt bits are defined as:

  (high bits) IbsOpCtl[26:20] = IbsOpMaxCnt[26:20]
  (low bits)  IbsOpCtl[15:0]  = IbsOpMaxCnt[19:4]

Perf event sample period can be derived from MaxCnt bits as:

  sample_period = (high bits) | ((low_bits) << 4);

However, current code just masks MaxCnt bits and shifts all of them,
including high bits, which is incorrect. Fix it.

Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/r/20250115054438.1021-4-ravi.bangoria@amd.com

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index bd8919e7c3b171151e863b5ce2c1bcdf50a92405..f95542b75b916e5d21fe4f23f0c44f051f476e33 100644 (file)
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -271,7 +271,7 @@ static int perf_ibs_init(struct perf_event *event)
 {
        struct hw_perf_event *hwc = &event->hw;
        struct perf_ibs *perf_ibs;
-       u64 max_cnt, config;
+       u64 config;
        int ret;
 
        perf_ibs = get_ibs_pmu(event->attr.type);
@@ -313,10 +313,19 @@ static int perf_ibs_init(struct perf_event *event)
                if (!hwc->sample_period)
                        hwc->sample_period = 0x10;
        } else {
-               max_cnt = config & perf_ibs->cnt_mask;
+               u64 period = 0;
+
+               if (perf_ibs == &perf_ibs_op) {
+                       period = (config & IBS_OP_MAX_CNT) << 4;
+                       if (ibs_caps & IBS_CAPS_OPCNTEXT)
+                               period |= config & IBS_OP_MAX_CNT_EXT_MASK;
+               } else {
+                       period = (config & IBS_FETCH_MAX_CNT) << 4;
+               }
+
                config &= ~perf_ibs->cnt_mask;
-               event->attr.sample_period = max_cnt << 4;
-               hwc->sample_period = event->attr.sample_period;
+               event->attr.sample_period = period;
+               hwc->sample_period = period;
        }
 
        if (!hwc->sample_period)