selftests/powerpc/pmu/: Add interface test for mmcr0 exception bits

The testcase uses "instructions" event to verify two bits(PMAE and PMAO)
in Monitor Mode Control Register 0 (MMCR0). At the time of interrupt,
pmae bit ( which enables performance monitor exception ) is expected to
be cleared and pmao (which indicates performance monitor alert) bit is
expected to be set in MMCR0. And testcases handles these checks.

Signed-off-by: Athira Rajeev <[e-mail]>
[mpe: Add error checking, drop GET_MMCR_FIELD, add to .gitignore]
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

tools/testing/selftests/powerpc/pmu/sampling_tests/.gitignore

···
+mmcr0_exceptionbits_test

tools/testing/selftests/powerpc/pmu/sampling_tests/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 CFLAGS += -m64
 
+TEST_GEN_PROGS := mmcr0_exceptionbits_test
+
 top_srcdir = ../../../../../..
 include ../../../lib.mk
 
-$(TEST_GEN_PROGS): ../../harness.c ../../utils.c ../event.c ../lib.c misc.c misc.h
+$(TEST_GEN_PROGS): ../../harness.c ../../utils.c ../event.c ../lib.c misc.c misc.h ../loop.S

tools/testing/selftests/powerpc/pmu/sampling_tests/mmcr0_exceptionbits_test.c

···
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2022, Athira Rajeev, IBM Corp.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "../event.h"
+#include "misc.h"
+#include "utils.h"
+
+extern void thirty_two_instruction_loop(int loops);
+
+/*
+ * A perf sampling test for mmcr0
+ * fields : pmae, pmao.
+ */
+static int mmcr0_exceptionbits(void)
+{
+	struct event event;
+	u64 *intr_regs;
+
+	/* Check for platform support for the test */
+	SKIP_IF(check_pvr_for_sampling_tests());
+
+	/* Init the event for the sampling test */
+	event_init_sampling(&event, 0x500fa);
+	event.attr.sample_regs_intr = platform_extended_mask;
+	FAIL_IF(event_open(&event));
+	event.mmap_buffer = event_sample_buf_mmap(event.fd, 1);
+
+	FAIL_IF(event_enable(&event));
+
+	/* workload to make the event overflow */
+	thirty_two_instruction_loop(10000);
+
+	FAIL_IF(event_disable(&event));
+
+	/* Check for sample count */
+	FAIL_IF(!collect_samples(event.mmap_buffer));
+
+	intr_regs = get_intr_regs(&event, event.mmap_buffer);
+
+	/* Check for intr_regs */
+	FAIL_IF(!intr_regs);
+
+	/* Verify that pmae is cleared and pmao is set in MMCR0 */
+	FAIL_IF(get_mmcr0_pmae(get_reg_value(intr_regs, "MMCR0"), 5));
+	FAIL_IF(!get_mmcr0_pmao(get_reg_value(intr_regs, "MMCR0"), 5));
+
+	event_close(&event);
+	return 0;
+}
+
+int main(void)
+{
+	return test_harness(mmcr0_exceptionbits, "mmcr0_exceptionbits");
+}