[PATCH 3/3] KVM: arm64: selftests: arch_timer_edge_cases - workaround for AC03_CPU_14

[Sebastian Ott]

arch_timer_edge_cases currently fails on ampere-one machines with
the following assertion failure:

==== Test Assertion Failure ====
  arm64/arch_timer_edge_cases.c:169: timer_condition == istatus
  pid=11236 tid=11236 errno=4 - Interrupted system call
     1  0x0000000000404ce7: test_run at arch_timer_edge_cases.c:938
     2  0x0000000000401ebb: main at arch_timer_edge_cases.c:1053
     3  0x0000ffff9fa8625b: ?? ??:0
     4  0x0000ffff9fa8633b: ?? ??:0
     5  0x0000000000401fef: _start at ??:?
  0x1 != 0x0 (timer_condition != istatus)

Meaning that the timer condition was met and an interrupt
was presented but the timer status bit in the control register
was not set.

This happens due to AC03_CPU_14 "Timer CVAL programming of a delta
greater than 2^63 will result in incorrect behavior."

Work around this issue by reducing the value that is used to reset
the counter and thus reduce the delta.

Link: https://lore.kernel.org/kvmarm/ac1de1d2-ef2b-d439-dc48-8615e121b07b@redhat.com
Link: https://amperecomputing.com/assets/AmpereOne_Developer_ER_v0_80_20240823_28945022f4.pdf
Signed-off-by: Sebastian Ott <sebott at redhat.com>
---
 tools/testing/selftests/kvm/arm64/arch_timer_edge_cases.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/arm64/arch_timer_edge_cases.c b/tools/testing/selftests/kvm/arm64/arch_timer_edge_cases.c
index a813b4c6c817..2f0397df0aa6 100644
--- a/tools/testing/selftests/kvm/arm64/arch_timer_edge_cases.c
+++ b/tools/testing/selftests/kvm/arm64/arch_timer_edge_cases.c
@@ -31,7 +31,7 @@ static const int32_t TVAL_MIN = INT32_MIN;
 static const uint32_t TIMEOUT_NO_IRQ_US = 50000;
 
 /* A nice counter value to use as the starting one for most tests. */
-static const uint64_t DEF_CNT = (CVAL_MAX / 2);
+static const uint64_t DEF_CNT = (CVAL_MAX / 4);
 
 /* Number of runs. */
 static const uint32_t NR_TEST_ITERS_DEF = 5;
-- 
2.49.0