[PATCH V10 19/46] drm/tests: Add a few tests around drm_fixed.h

[Maíra Canal]

Hi Alex,

On 17/06/25 01:17, Alex Hung wrote:
> From: Harry Wentland <harry.wentland at amd.com>
> 
> While working on the CTM implementation of VKMS I had to ascertain
> myself of a few assumptions. One of those is whether drm_fixed.h
> treats its numbers using signed-magnitude or twos-complement. It is
> twos-complement.
> 
> In order to make someone else's day easier I am adding the
> drm_test_int2fixp test that validates the above assumption.
> 
> I am also adding a test for the new sm2fixp function that converts
> from a signed-magnitude fixed point to the twos-complement fixed
> point.
> 
> Reviewed-by: Louis Chauvet <louis.chauvet at bootlin.com>
> Signed-off-by: Alex Hung <alex.hung at amd.com>
> Signed-off-by: Harry Wentland <harry.wentland at amd.com>
> Reviewed-by: Daniel Stone <daniels at collabora.com>
> ---
> v7:
>   - Fix checkpatch warnings (Louis Chauvet)
> 
> v6:
>   - add missing MODULE_DESCRIPTION (Jeff Johnson)
>   - fix buffer overflow
> 
> 
>   drivers/gpu/drm/tests/Makefile        |  3 +-
>   drivers/gpu/drm/tests/drm_fixp_test.c | 71 +++++++++++++++++++++++++++
>   2 files changed, 73 insertions(+), 1 deletion(-)
>   create mode 100644 drivers/gpu/drm/tests/drm_fixp_test.c
> 
> diff --git a/drivers/gpu/drm/tests/Makefile b/drivers/gpu/drm/tests/Makefile
> index 3afd6587df08..91437cf34d92 100644
> --- a/drivers/gpu/drm/tests/Makefile
> +++ b/drivers/gpu/drm/tests/Makefile
> @@ -23,6 +23,7 @@ obj-$(CONFIG_DRM_KUNIT_TEST) += \
>   	drm_modes_test.o \
>   	drm_plane_helper_test.o \
>   	drm_probe_helper_test.o \
> -	drm_rect_test.o
> +	drm_rect_test.o	\
> +	drm_fixp_test.o
>   
>   CFLAGS_drm_mm_test.o := $(DISABLE_STRUCTLEAK_PLUGIN)
> diff --git a/drivers/gpu/drm/tests/drm_fixp_test.c b/drivers/gpu/drm/tests/drm_fixp_test.c
> new file mode 100644
> index 000000000000..de91177af213
> --- /dev/null
> +++ b/drivers/gpu/drm/tests/drm_fixp_test.c
> @@ -0,0 +1,71 @@
> +// SPDX-License-Identifier: MIT
> +/*
> + * Copyright 2022 Advanced Micro Devices, Inc.
> + */
> +
> +#include <kunit/test.h>
> +#include <drm/drm_fixed.h>
> +
> +static void drm_test_sm2fixp(struct kunit *test)
> +{
> +	KUNIT_EXPECT_EQ(test, 0x7fffffffffffffffll, ((1ull << 63) - 1));
> +
> +	/* 1 */
> +	KUNIT_EXPECT_EQ(test, drm_int2fixp(1), drm_sm2fixp(1ull << DRM_FIXED_POINT));
> +
> +	/* -1 */
> +	KUNIT_EXPECT_EQ(test, drm_int2fixp(-1),
> +			drm_sm2fixp((1ull << 63) | (1ull << DRM_FIXED_POINT)));
> +
> +	/* 0.5 */
> +	KUNIT_EXPECT_EQ(test, drm_fixp_from_fraction(1, 2),
> +			drm_sm2fixp(1ull << (DRM_FIXED_POINT - 1)));
> +
> +	/* -0.5 */
> +	KUNIT_EXPECT_EQ(test, drm_fixp_from_fraction(-1, 2),
> +			drm_sm2fixp((1ull << 63) | (1ull << (DRM_FIXED_POINT - 1))));
> +}
> +
> +static void drm_test_int2fixp(struct kunit *test)
> +{
> +	/* 1 */
> +	KUNIT_EXPECT_EQ(test, 1ll << 32, drm_int2fixp(1));
> +
> +	/* -1 */
> +	KUNIT_EXPECT_EQ(test, -(1ll << 32), drm_int2fixp(-1));
> +
> +	/* 1 + (-1) = 0 */
> +	KUNIT_EXPECT_EQ(test, 0, drm_int2fixp(1) + drm_int2fixp(-1));
> +
> +	/* 1 / 2 */
> +	KUNIT_EXPECT_EQ(test, 1ll << 31, drm_fixp_from_fraction(1, 2));
> +
> +	/* -0.5 */
> +	KUNIT_EXPECT_EQ(test, -(1ll << 31), drm_fixp_from_fraction(-1, 2));
> +
> +	/* (1 / 2) + (-1) = 0.5 */
> +	KUNIT_EXPECT_EQ(test, 1ll << 31, drm_fixp_from_fraction(-1, 2) + drm_int2fixp(1));
> +
> +	/* (1 / 2) - 1) = 0.5 */
> +	KUNIT_EXPECT_EQ(test, -(1ll << 31), drm_fixp_from_fraction(1, 2) + drm_int2fixp(-1));
> +
> +	/* (1 / 2) - 1) = 0.5 */
> +	KUNIT_EXPECT_EQ(test, -(1ll << 31), drm_fixp_from_fraction(1, 2) - drm_int2fixp(1));
> +}
> +
> +static struct kunit_case drm_fixp_tests[] = {
> +	KUNIT_CASE(drm_test_int2fixp),
> +	KUNIT_CASE(drm_test_sm2fixp),
> +	{ }
> +};
> +
> +static struct kunit_suite drm_rect_test_suite = {

Instead of `drm_rect_test_suite`, how about `drm_fixp_test_suite`?

> +	.name = "drm_fixp",
> +	.test_cases = drm_fixp_tests,
> +};
> +
> +kunit_test_suite(drm_rect_test_suite);
> +
> +MODULE_AUTHOR("AMD");
> +MODULE_LICENSE("GPL and additional rights");

 From the kernel docs, "GPL and additional rights" shouldn't be used in
new code [1].

[1] https://docs.kernel.org/process/license-rules.html#id1

Best Regards,
- Maíra

> +MODULE_DESCRIPTION("Unit tests for drm_fixed.h");