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drm/tests: Add a few tests around drm_fixed.h

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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@bootlin.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Simon Ser <contact@emersion.fr>
Link: https://patch.msgid.link/20251115000237.3561250-22-alex.hung@amd.com
This commit is contained in:
Harry Wentland 2025-11-14 17:01:46 -07:00 committed by Simon Ser
parent ea3f6baf31
commit b7f513803b
2 changed files with 73 additions and 1 deletions
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3
drivers/gpu/drm/tests/Makefile
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@ -24,6 +24,7 @@ obj-$(CONFIG_DRM_KUNIT_TEST) += \
drm_plane_helper_test.o \
drm_probe_helper_test.o \
drm_rect_test.o \
drm_sysfb_modeset_test.o
drm_sysfb_modeset_test.o \
drm_fixp_test.o
CFLAGS_drm_mm_test.o := $(DISABLE_STRUCTLEAK_PLUGIN)

71
drivers/gpu/drm/tests/drm_fixp_test.c Normal file
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@ -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_fixp_test_suite = {
.name = "drm_fixp",
.test_cases = drm_fixp_tests,
};
kunit_test_suite(drm_fixp_test_suite);
MODULE_AUTHOR("AMD");
MODULE_LICENSE("Dual MIT/GPL");
MODULE_DESCRIPTION("Unit tests for drm_fixed.h");