selftests/powerpc: Add test for system wide DSCR default

This patch adds a test case for the system wide DSCR default value,
which when changed through it's sysfs interface must be visible to all
threads reading DSCR either through the privilege state SPR or the
problem state SPR. The DSCR value change should be immediate as well.
Acked-by: Shuah Khan <shuahkh@osg.samsung.com>
Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

tools/testing/selftests/powerpc/Makefile

@@ -12,7 +12,7 @@ CFLAGS := -Wall -O2 -flto -Wall -Werror -DGIT_VERSION='"$(GIT_VERSION)"' -I$(CUR
 
 export CFLAGS
 
-SUB_DIRS = pmu copyloops mm tm primitives stringloops vphn switch_endian
+SUB_DIRS = pmu copyloops mm tm primitives stringloops vphn switch_endian dscr
 
 endif
 

tools/testing/selftests/powerpc/dscr/Makefile

+TEST_PROGS := dscr_default_test
+
+dscr_default_test: LDLIBS += -lpthread
+
+all: $(TEST_PROGS)
+
+$(TEST_PROGS): ../harness.c
+
+include ../../lib.mk
+
+clean:
+	rm -f $(TEST_PROGS) *.o

tools/testing/selftests/powerpc/dscr/dscr.h

+/*
+ * POWER Data Stream Control Register (DSCR)
+ *
+ * This header file contains helper functions and macros
+ * required for all the DSCR related test cases.
+ *
+ * Copyright 2012, Anton Blanchard, IBM Corporation.
+ * Copyright 2015, Anshuman Khandual, IBM Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published
+ * by the Free Software Foundation.
+ */
+#ifndef _SELFTESTS_POWERPC_DSCR_DSCR_H
+#define _SELFTESTS_POWERPC_DSCR_DSCR_H
+
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <fcntl.h>
+#include <dirent.h>
+#include <pthread.h>
+#include <sched.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+#include "utils.h"
+
+#define SPRN_DSCR	0x11	/* Privilege state SPR */
+#define SPRN_DSCR_USR	0x03	/* Problem state SPR */
+#define THREADS		100	/* Max threads */
+#define COUNT		100	/* Max iterations */
+#define DSCR_MAX	16	/* Max DSCR value */
+#define LEN_MAX		100	/* Max name length */
+
+#define DSCR_DEFAULT	"/sys/devices/system/cpu/dscr_default"
+#define CPU_PATH	"/sys/devices/system/cpu/"
+
+#define rmb()  asm volatile("lwsync":::"memory")
+#define wmb()  asm volatile("lwsync":::"memory")
+
+#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))
+
+/* Prilvilege state DSCR access */
+inline unsigned long get_dscr(void)
+{
+	unsigned long ret;
+
+	asm volatile("mfspr %0,%1" : "=r" (ret): "i" (SPRN_DSCR));
+
+	return ret;
+}
+
+inline void set_dscr(unsigned long val)
+{
+	asm volatile("mtspr %1,%0" : : "r" (val), "i" (SPRN_DSCR));
+}
+
+/* Problem state DSCR access */
+inline unsigned long get_dscr_usr(void)
+{
+	unsigned long ret;
+
+	asm volatile("mfspr %0,%1" : "=r" (ret): "i" (SPRN_DSCR_USR));
+
+	return ret;
+}
+
+inline void set_dscr_usr(unsigned long val)
+{
+	asm volatile("mtspr %1,%0" : : "r" (val), "i" (SPRN_DSCR_USR));
+}
+
+/* Default DSCR access */
+unsigned long get_default_dscr(void)
+{
+	int fd = -1, ret;
+	char buf[16];
+	unsigned long val;
+
+	if (fd == -1) {
+		fd = open(DSCR_DEFAULT, O_RDONLY);
+		if (fd == -1) {
+			perror("open() failed");
+			exit(1);
+		}
+	}
+	memset(buf, 0, sizeof(buf));
+	lseek(fd, 0, SEEK_SET);
+	ret = read(fd, buf, sizeof(buf));
+	if (ret == -1) {
+		perror("read() failed");
+		exit(1);
+	}
+	sscanf(buf, "%lx", &val);
+	close(fd);
+	return val;
+}
+
+void set_default_dscr(unsigned long val)
+{
+	int fd = -1, ret;
+	char buf[16];
+
+	if (fd == -1) {
+		fd = open(DSCR_DEFAULT, O_RDWR);
+		if (fd == -1) {
+			perror("open() failed");
+			exit(1);
+		}
+	}
+	sprintf(buf, "%lx\n", val);
+	ret = write(fd, buf, strlen(buf));
+	if (ret == -1) {
+		perror("write() failed");
+		exit(1);
+	}
+	close(fd);
+}
+
+double uniform_deviate(int seed)
+{
+	return seed * (1.0 / (RAND_MAX + 1.0));
+}
+#endif	/* _SELFTESTS_POWERPC_DSCR_DSCR_H */

tools/testing/selftests/powerpc/dscr/dscr_default_test.c

+/*
+ * POWER Data Stream Control Register (DSCR) default test
+ *
+ * This test modifies the system wide default DSCR through
+ * it's sysfs interface and then verifies that all threads
+ * see the correct changed DSCR value immediately.
+ *
+ * Copyright 2012, Anton Blanchard, IBM Corporation.
+ * Copyright 2015, Anshuman Khandual, IBM Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published
+ * by the Free Software Foundation.
+ */
+#include "dscr.h"
+
+static unsigned long dscr;		/* System DSCR default */
+static unsigned long sequence;
+static unsigned long result[THREADS];
+
+static void *do_test(void *in)
+{
+	unsigned long thread = (unsigned long)in;
+	unsigned long i;
+
+	for (i = 0; i < COUNT; i++) {
+		unsigned long d, cur_dscr, cur_dscr_usr;
+		unsigned long s1, s2;
+
+		s1 = ACCESS_ONCE(sequence);
+		if (s1 & 1)
+			continue;
+		rmb();
+
+		d = dscr;
+		cur_dscr = get_dscr();
+		cur_dscr_usr = get_dscr_usr();
+
+		rmb();
+		s2 = sequence;
+
+		if (s1 != s2)
+			continue;
+
+		if (cur_dscr != d) {
+			fprintf(stderr, "thread %ld kernel DSCR should be %ld "
+				"but is %ld\n", thread, d, cur_dscr);
+			result[thread] = 1;
+			pthread_exit(&result[thread]);
+		}
+
+		if (cur_dscr_usr != d) {
+			fprintf(stderr, "thread %ld user DSCR should be %ld "
+				"but is %ld\n", thread, d, cur_dscr_usr);
+			result[thread] = 1;
+			pthread_exit(&result[thread]);
+		}
+	}
+	result[thread] = 0;
+	pthread_exit(&result[thread]);
+}
+
+int dscr_default(void)
+{
+	pthread_t threads[THREADS];
+	unsigned long i, *status[THREADS];
+	unsigned long orig_dscr_default;
+
+	orig_dscr_default = get_default_dscr();
+
+	/* Initial DSCR default */
+	dscr = 1;
+	set_default_dscr(dscr);
+
+	/* Spawn all testing threads */
+	for (i = 0; i < THREADS; i++) {
+		if (pthread_create(&threads[i], NULL, do_test, (void *)i)) {
+			perror("pthread_create() failed");
+			goto fail;
+		}
+	}
+
+	srand(getpid());
+
+	/* Keep changing the DSCR default */
+	for (i = 0; i < COUNT; i++) {
+		double ret = uniform_deviate(rand());
+
+		if (ret < 0.0001) {
+			sequence++;
+			wmb();
+
+			dscr++;
+			if (dscr > DSCR_MAX)
+				dscr = 0;
+
+			set_default_dscr(dscr);
+
+			wmb();
+			sequence++;
+		}
+	}
+
+	/* Individual testing thread exit status */
+	for (i = 0; i < THREADS; i++) {
+		if (pthread_join(threads[i], (void **)&(status[i]))) {
+			perror("pthread_join() failed");
+			goto fail;
+		}
+
+		if (*status[i]) {
+			printf("%ldth thread failed to join with %ld status\n",
+								i, *status[i]);
+			goto fail;
+		}
+	}
+	set_default_dscr(orig_dscr_default);
+	return 0;
+fail:
+	set_default_dscr(orig_dscr_default);
+	return 1;
+}
+
+int main(int argc, char *argv[])
+{
+	return test_harness(dscr_default, "dscr_default_test");
+}