FEAT_PMUv3_TH (Armv8.8) permits a PMU counter to increment only on
events whose count meets a specified threshold condition. For example if
PMEVTYPERn.TC (Threshold Control) is set to 0b101 (Greater than or
equal, count), and the threshold is set to 2, then the PMU counter will
now only increment by 1 when an event would have previously incremented
the PMU counter by 2 or more on a single processor cycle.

Three new Perf event config fields, 'threshold', 'threshold_compare' and
'threshold_count' have been added to control the feature.
threshold_compare maps to the upper two bits of PMEVTYPERn.TC and
threshold_count maps to the first bit of TC. These separate attributes
have been picked rather than enumerating all the possible combinations
of the TC field as in the Arm ARM. The attributes would be used on a
Perf command line like this:

  $ perf stat -e stall_slot/threshold=2,threshold_compare=2/

A new capability for reading out the maximum supported threshold value
has also been added:

  $ cat /sys/bus/event_source/devices/armv8_pmuv3/caps/threshold_max

  0x000000ff

If a threshold higher than threshold_max is provided, then an error is
generated. If FEAT_PMUv3_TH isn't implemented or a 32 bit kernel is
running, then threshold_max reads zero, and attempting to set a
threshold value will also result in an error.

The threshold is per PMU counter, and there are potentially different
threshold_max values per PMU type on heterogeneous systems.

Bits higher than 32 now need to be written into PMEVTYPER, so
armv8pmu_write_evtype() has to be updated to take an unsigned long value
rather than u32 which gives the correct behavior on both aarch32 and 64.
Signed-off-by: James Clark <james.clark@arm.com>
Link: https://lore.kernel.org/r/20231211161331.1277825-11-james.clark@arm.comSigned-off-by: Will Deacon <will@kernel.org>