[PATCH 09/11] drm/vkms: test sRGB and inverse sRGB LUTs using more samples

We're currently using srgb_eotf.lut_length samples in
vkms_color_srgb_inv_srgb(). This does not exercise any points that are
not in the forward sRGB LUT, although it exercises points that are not
in its inverse.

Let's test with more samples, to also exercise points that are not in
the forward sRGB LUT.

We chose 4096 samples. LUT inputs are u16, so we could have up to 65536
samples. LUT sizes are usually not higher than 512, so with 4096 we have
at least 8 samples between each LUT point.

We can see a minor error bump with this change. In the next commits we
replace such LUTs with non-uniform optimal ones to reduce the error.

Signed-off-by: Leandro Ribeiro <[email protected]>
---
 drivers/gpu/drm/vkms/tests/vkms_color_test.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/vkms/tests/vkms_color_test.c b/drivers/gpu/drm/vkms/tests/vkms_color_test.c
index 571b1b579310..78f67bba33b5 100644
--- a/drivers/gpu/drm/vkms/tests/vkms_color_test.c
+++ b/drivers/gpu/drm/vkms/tests/vkms_color_test.c
@@ -123,14 +123,16 @@ static void vkms_color_test_linear(struct kunit *test)
 static void vkms_color_srgb_inv_srgb(struct kunit *test)
 {
 	u16 srgb, final;
-	u16 tolerance = 119;
+	u16 tolerance = 122;
+	u32 x;
 
-	for (int i = 0; i < srgb_eotf.lut_length; i++) {
-		srgb = apply_lut_to_channel_value(&srgb_eotf, srgb_eotf.x[i], LUT_RED);
+	for (u32 i = 0; i <= 4095; i++) {
+		x = i * U16_MAX / 4095;
+		srgb = apply_lut_to_channel_value(&srgb_eotf, x, LUT_RED);
 		final = apply_lut_to_channel_value(&srgb_inv_eotf, srgb, LUT_RED);
 
-		KUNIT_EXPECT_GE(test, final, (int)srgb_eotf.x[i] - tolerance);
-		KUNIT_EXPECT_LE(test, final, (int)srgb_eotf.x[i] + tolerance);
+		KUNIT_EXPECT_GE(test, final, (int)x - tolerance);
+		KUNIT_EXPECT_LE(test, final, (int)x + tolerance);
 	}
 }
 
-- 
2.55.0