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Message-Id: <20251013-iio-tests-fixed-point-new-kunit-v1-1-7b52021925e6@baylibre.com>
Date: Mon, 13 Oct 2025 16:33:43 -0500
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>,
Nuno Sá <nuno.sa@...log.com>,
Andy Shevchenko <andy@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
David Lechner <dlechner@...libre.com>
Subject: [PATCH] iio: test: fixed-point: new kunit test
Add a kunit test for iio_str_to_fixpoint(). This function has an
unintuitive API so this is helpful to see how to use it and shows the
various edge cases.
Signed-off-by: David Lechner <dlechner@...libre.com>
---
When reviewing [1], I noticed that iio_str_to_fixpoint() has an odd API
which lead me to find the bug in [2]. To make sure I was understanding
the API correctly, I wrote a KUnit test for it. So here it is.
[1]: https://lore.kernel.org/linux-iio/20251009173609.992452-3-flavra@baylibre.com/
[2]: https://lore.kernel.org/linux-iio/20251010-iio-adc-ad7280a-fix-ad7280_store_balance_timer-v1-1-e11746735192@baylibre.com/
---
Discussion unrelated to the patch:
I'm also a little tempted to introduce a new function that is a bit
easier to use. Many callers of iio_str_to_fixpoint_s64() are doing
something like int_part * 1000 + fract_part and ignoring the possibility
of negative values which require special handling.
static int iio_str_to_fixpoint_s64(const char *str, u32 decimal_places, s64 *value)
{
int int_part, fract_part;
int ret;
ret = iio_str_to_fixpoint(str, int_pow(10, decimal_places - 1),
&int_part, &fract_part);
if (ret)
return ret;
*value = (s64)int_part * int_pow(10, decimal_places) +
(int_part < 0 ? -1 : 1) * fract_part;
return 0;
}
---
drivers/iio/test/Kconfig | 13 ++++++++
drivers/iio/test/Makefile | 1 +
drivers/iio/test/iio-test-fixed-point.c | 58 +++++++++++++++++++++++++++++++++
3 files changed, 72 insertions(+)
diff --git a/drivers/iio/test/Kconfig b/drivers/iio/test/Kconfig
index 6e65e929791ca247df9ac993fddbb4da557d5dfa..d210067ea59199d342b15bf373e724d0aa2c55a0 100644
--- a/drivers/iio/test/Kconfig
+++ b/drivers/iio/test/Kconfig
@@ -4,6 +4,19 @@
#
# Keep in alphabetical order
+
+config IIO_FIXED_POINT_KUNIT_TEST
+ tristate "Test IIO fixedpoint functions" if !KUNIT_ALL_TESTS
+ depends on KUNIT
+ default KUNIT_ALL_TESTS
+ help
+ Build unit tests for the IIO fixed-point code.
+
+ For more information on KUnit and unit tests in general, please refer
+ to the KUnit documentation in Documentation/dev-tools/kunit/.
+
+ If unsure, say N.
+
config IIO_GTS_KUNIT_TEST
tristate "Test IIO gain-time-scale helpers" if !KUNIT_ALL_TESTS
depends on KUNIT
diff --git a/drivers/iio/test/Makefile b/drivers/iio/test/Makefile
index 0c846bc21acda5a487b3a6977a8e9feaef20159a..a580e78b0fe00adc65f8f9df80023d6d738d11f7 100644
--- a/drivers/iio/test/Makefile
+++ b/drivers/iio/test/Makefile
@@ -4,6 +4,7 @@
#
# Keep in alphabetical order
+obj-$(CONFIG_IIO_FIXED_POINT_KUNIT_TEST) += iio-test-fixed-point.o
obj-$(CONFIG_IIO_RESCALE_KUNIT_TEST) += iio-test-rescale.o
obj-$(CONFIG_IIO_FORMAT_KUNIT_TEST) += iio-test-format.o
obj-$(CONFIG_IIO_GTS_KUNIT_TEST) += iio-test-gts.o
diff --git a/drivers/iio/test/iio-test-fixed-point.c b/drivers/iio/test/iio-test-fixed-point.c
new file mode 100644
index 0000000000000000000000000000000000000000..edfed5434af2391a31d206fda2be0455a9e5e443
--- /dev/null
+++ b/drivers/iio/test/iio-test-fixed-point.c
@@ -0,0 +1,58 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Unit tests for IIO fixed-point functions
+ *
+ * Copyright (c) 2025 BayLibre, SAS
+ */
+
+#include <kunit/test.h>
+#include <linux/iio/iio.h>
+#include <linux/math.h>
+#include <linux/types.h>
+
+static void iio_test_iio_str_to_fixed_point(struct kunit *test)
+{
+ int int_part, fract_part;
+ int ret;
+
+ /* Positive value > 1 */
+ ret = iio_str_to_fixpoint("1.234", 100, &int_part, &fract_part);
+ KUNIT_EXPECT_EQ(test, 0, ret);
+ KUNIT_EXPECT_EQ(test, int_part * 1000 + fract_part, 1234);
+
+ /* Truncates rather than rounding closest. */
+ ret = iio_str_to_fixpoint("1.234567", 100, &int_part, &fract_part);
+ KUNIT_EXPECT_EQ(test, 0, ret);
+ KUNIT_EXPECT_EQ(test, int_part * 1000 + fract_part, 1234);
+
+ /* Positive value < 1 */
+ ret = iio_str_to_fixpoint("0.001", 100, &int_part, &fract_part);
+ KUNIT_EXPECT_EQ(test, 0, ret);
+ KUNIT_EXPECT_EQ(test, int_part * 1000 + fract_part, 1);
+
+ /* Negative value > -1 */
+ ret = iio_str_to_fixpoint("-0.001", 100, &int_part, &fract_part);
+ KUNIT_EXPECT_EQ(test, 0, ret);
+ KUNIT_EXPECT_EQ(test, int_part * 1000 + fract_part, -1);
+
+ /* Negative value < -1 */
+ ret = iio_str_to_fixpoint("-1.001", 100, &int_part, &fract_part);
+ KUNIT_EXPECT_EQ(test, 0, ret);
+ /* The fractional part is subtracted rather than added in this case! */
+ KUNIT_EXPECT_EQ(test, int_part * 1000 - fract_part, -1001);
+}
+
+static const struct kunit_case iio_fixed_point_test_cases[] = {
+ KUNIT_CASE(iio_test_iio_str_to_fixed_point),
+ { }
+};
+
+static struct kunit_suite iio_fixed_point_test_suite = {
+ .name = "iio-fixed-point",
+ .test_cases = iio_fixed_point_test_cases,
+};
+kunit_test_suite(iio_fixed_point_test_suite);
+
+MODULE_AUTHOR("David Lechner <dlechner@...libre.com>");
+MODULE_DESCRIPTION("Test IIO fixed-point functions");
+MODULE_LICENSE("GPL");
---
base-commit: a9682f53c2d1678b93a123cdaa260e955430bc5c
change-id: 20251010-iio-tests-fixed-point-new-kunit-5a0d3eb19865
Best regards,
--
David Lechner <dlechner@...libre.com>
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