helpers: Introduce retry macro

Introduce a macro retry(attempts, condition, expr) for retrying a
condition, which is extensively used in coreboot.

Example usage:

 if (!retry(3, read32(REG) == 0, mdelay(1))
         printk(BIOS_ERR, "Error waiting for REG to be 0\n");

BUG=none
TEST=make tests/commonlib/bsd/helpers-test
TEST=emerge-cherry coreboot
BRANCH=none

Change-Id: I421e4dcab949616bd68b3a14231da744b9f74eeb
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55778
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Julius Werner <jwerner@chromium.org>

src/commonlib/bsd/include/commonlib/bsd/helpers.h

@@ -88,4 +88,39 @@
 /* Calculate size of structure member. */
 #define member_size(type, member)	(sizeof(((type *)0)->member))
 
+#define _retry_impl(attempts, condition, expr, ...)	\
+({							\
+	__typeof__(condition) _retry_ret =		\
+		(__typeof__(condition))0;		\
+	int _retry_attempts = (attempts);		\
+	do {						\
+		_retry_ret = (condition);		\
+		if (_retry_ret)				\
+			break;				\
+		if (--_retry_attempts > 0) {		\
+			expr;				\
+		} else {				\
+			break;				\
+		}					\
+	} while (1);					\
+	_retry_ret;					\
+})
+
+/*
+ * Helper macro to retry until a condition becomes true or the maximum number
+ * of attempts is reached. Two forms are supported:
+ *
+ * 1. retry(attempts, condition)
+ * 2. retry(attempts, condition, expr)
+ *
+ * @param attempts	Maximum attempts.
+ * @param condition	Condition to retry for.
+ * @param expr		Procedure to run between each evaluation to "condition".
+ *
+ * @return Condition value if it evaluates to true within the maximum attempts;
+ *	   0 otherwise.
+ */
+#define retry(attempts, condition, ...) \
+	_retry_impl(attempts, condition, __VA_ARGS__)
+
 #endif /* COMMONLIB_BSD_HELPERS_H */

tests/commonlib/Makefile.inc

@@ -1,5 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
+subdirs-y += bsd
+
 tests-y += region-test
 
 region-test-srcs += tests/commonlib/region-test.c

tests/commonlib/bsd/Makefile.inc

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+tests-y += helpers-test
+
+helpers-test-srcs += tests/commonlib/bsd/helpers-test.c

tests/commonlib/bsd/helpers-test.c

@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <commonlib/bsd/helpers.h>
+#include <tests/test.h>
+
+static void func(void)
+{
+	function_called();
+}
+
+static void test_retry(void **state)
+{
+	int count;
+
+	/* 2-argument form */
+	count = 0;
+	assert_true(retry(3, ++count == 1));
+	count = 0;
+	assert_true(retry(3, ++count == 3));
+	count = 0;
+	assert_false(retry(3, ++count == 4));
+
+	/* 3-argument form */
+	expect_function_calls(func, 9);
+	assert_null(retry(10, NULL, func()));
+
+	assert_int_equal(retry(10, 999, func()), 999);
+
+	count = 0;
+	expect_function_calls(func, 3);
+	assert_true(retry(10, ++count == 4, func()));
+}
+
+int main(void)
+{
+	const struct CMUnitTest tests[] = {
+		cmocka_unit_test(test_retry),
+	};
+
+	return cmocka_run_group_tests(tests, NULL, NULL);
+}