drm/tests: Add test cases for drm_rect_calc_hscale()

Insert parameterized test for the drm_rect_calc_hscale() to ensure
correctness and prevent future regressions. Besides the test for the
usual case, tests the exceptions.
Signed-off-by: Arthur Grillo <arthurgrillo@riseup.net>
Reviewed-by: Maíra Canal <mcanal@igalia.com>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20230418230146.461129-3-arthurgrillo@riseup.net

drivers/gpu/drm/tests/drm_rect_test.c

@@ -10,6 +10,7 @@
 #include <drm/drm_rect.h>
 
 #include <linux/string_helpers.h>
+#include <linux/errno.h>
 
 static void drm_rect_compare(struct kunit *test, const struct drm_rect *r,
 			     const struct drm_rect *expected)
@@ -343,12 +344,83 @@ static void drm_test_rect_intersect(struct kunit *test)
 	drm_rect_compare(test, &r1_aux, &params->expected_intersection);
 }
 
+struct drm_rect_scale_case {
+	const char *name;
+	struct drm_rect src, dst;
+	int min_range, max_range;
+	int expected_scaling_factor;
+};
+
+static const struct drm_rect_scale_case drm_rect_scale_cases[] = {
+	{
+		.name = "normal use",
+		.src = DRM_RECT_INIT(0, 0, 2 << 16, 2 << 16),
+		.dst = DRM_RECT_INIT(0, 0, 1 << 16, 1 << 16),
+		.min_range = 0, .max_range = INT_MAX,
+		.expected_scaling_factor = 2,
+	},
+	{
+		.name = "out of max range",
+		.src = DRM_RECT_INIT(0, 0, 10 << 16, 10 << 16),
+		.dst = DRM_RECT_INIT(0, 0, 1 << 16, 1 << 16),
+		.min_range = 3, .max_range = 5,
+		.expected_scaling_factor = -ERANGE,
+	},
+	{
+		.name = "out of min range",
+		.src = DRM_RECT_INIT(0, 0, 2 << 16, 2 << 16),
+		.dst = DRM_RECT_INIT(0, 0, 1 << 16, 1 << 16),
+		.min_range = 3, .max_range = 5,
+		.expected_scaling_factor = -ERANGE,
+	},
+	{
+		.name = "zero dst",
+		.src = DRM_RECT_INIT(0, 0, 2 << 16, 2 << 16),
+		.dst = DRM_RECT_INIT(0, 0, 0 << 16, 0 << 16),
+		.min_range = 0, .max_range = INT_MAX,
+		.expected_scaling_factor = 0,
+	},
+	{
+		.name = "negative src",
+		.src = DRM_RECT_INIT(0, 0, -(1 << 16), -(1 << 16)),
+		.dst = DRM_RECT_INIT(0, 0, 1 << 16, 1 << 16),
+		.min_range = 0, .max_range = INT_MAX,
+		.expected_scaling_factor = -EINVAL,
+	},
+	{
+		.name = "negative dst",
+		.src = DRM_RECT_INIT(0, 0, 1 << 16, 1 << 16),
+		.dst = DRM_RECT_INIT(0, 0, -(1 << 16), -(1 << 16)),
+		.min_range = 0, .max_range = INT_MAX,
+		.expected_scaling_factor = -EINVAL,
+	},
+};
+
+static void drm_rect_scale_case_desc(const struct drm_rect_scale_case *t, char *desc)
+{
+	strscpy(desc, t->name, KUNIT_PARAM_DESC_SIZE);
+}
+
+KUNIT_ARRAY_PARAM(drm_rect_scale, drm_rect_scale_cases, drm_rect_scale_case_desc);
+
+static void drm_test_rect_calc_hscale(struct kunit *test)
+{
+	const struct drm_rect_scale_case *params = test->param_value;
+	int scaling_factor;
+
+	scaling_factor = drm_rect_calc_hscale(&params->src, &params->dst,
+					      params->min_range, params->max_range);
+
+	KUNIT_EXPECT_EQ(test, scaling_factor, params->expected_scaling_factor);
+}
+
 static struct kunit_case drm_rect_tests[] = {
 	KUNIT_CASE(drm_test_rect_clip_scaled_div_by_zero),
 	KUNIT_CASE(drm_test_rect_clip_scaled_not_clipped),
 	KUNIT_CASE(drm_test_rect_clip_scaled_clipped),
 	KUNIT_CASE(drm_test_rect_clip_scaled_signed_vs_unsigned),
 	KUNIT_CASE_PARAM(drm_test_rect_intersect, drm_rect_intersect_gen_params),
+	KUNIT_CASE_PARAM(drm_test_rect_calc_hscale, drm_rect_scale_gen_params),
 	{ }
 };