[igt-dev] [v2] tests/kms_color: Fix CRC mismatch issues with ctm test

[Shankar, Uma]

>-----Original Message-----
>From: Landwerlin, Lionel G
>Sent: Monday, March 25, 2019 7:11 AM
>To: Shankar, Uma <uma.shankar at intel.com>; igt-dev at lists.freedesktop.org
>Cc: Syrjala, Ville <ville.syrjala at intel.com>; Lankhorst, Maarten
><maarten.lankhorst at intel.com>
>Subject: Re: [igt-dev] [v2] tests/kms_color: Fix CRC mismatch issues with ctm test
>
>When degamma & gamma LUTs are disabled & CTM is enabled, i915 programs a
>linear table in the degamma/gamma LUTs :
>
>https://cgit.freedesktop.org/drm/drm-
>intel/tree/drivers/gpu/drm/i915/intel_color.c#n463
>https://cgit.freedesktop.org/drm/drm-
>intel/tree/drivers/gpu/drm/i915/intel_color.c#n495
>
>All the values programmed are in u16 range which is also what userspace can
>program (this applies to BDW/SKL/KBL).
>What is it that the kernel is able to program but not userspace?

Hi Lionel,
Issue is with representing 1.0 which needs a 3.16 kind of representation. So directly doing it in
Kernel to program linear luts using below:
for (i = 0; i < lut_size; i++) {
			u32 v = (i * (1 << 16)) / (lut_size - 1);
			I915_WRITE(PRE_CSC_GAMC_DATA(pipe), v);
		}
takes care of the corner case. The ABI is getting extended and we will need higher
precision luts, but for now due to lack of it,  putting the same to be done in driver.

Regards,
Uma Shankar

>-Lionel
>
>On 24/03/2019 17:55, Uma Shankar wrote:
>> Due to Gamma/Degamma limitation with precision (lack of exact 1.0
>> representation) due to ABI restriction, applying linear gamma affects
>> crc. This patch fixes the same by making ctm tests independant of
>> gamma/degamma.
>>
>> v2: Disable degamma/gamma programming for ctm max test as it leads to
>> crc mimsmatch. Limiting it to this test case alone as other tests need
>> it to be enabled, hence not touching those scenarios.
>>
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108147
>> Signed-off-by: Uma Shankar <uma.shankar at intel.com>
>> ---
>>   tests/kms_color.c | 16 ++++++++++++++--
>>   1 file changed, 14 insertions(+), 2 deletions(-)
>>
>> diff --git a/tests/kms_color.c b/tests/kms_color.c index
>> decf3c2..93560d4 100644
>> --- a/tests/kms_color.c
>> +++ b/tests/kms_color.c
>> @@ -696,8 +696,15 @@ static bool test_pipe_ctm(data_t *data,
>>   		igt_assert(fb_modeset_id);
>>   		igt_plane_set_fb(primary, &fb_modeset);
>>
>> -		set_degamma(data, primary->pipe, degamma_linear);
>> -		set_gamma(data, primary->pipe, gamma_linear);
>> +		/*
>> +		 * Don't program LUT's for max CTM cases as limitation of
>> +		 * representing 1.0 due to ABI limits causes crc mismatch
>> +		 */
>> +		if (memcmp(before, after, sizeof(color_t)))
>> +			set_degamma(data, primary->pipe, degamma_linear);
>> +			set_gamma(data, primary->pipe, gamma_linear);
>> +		}
>> +
>>   		disable_ctm(primary->pipe);
>>   		igt_display_commit(&data->display);
>>
>> @@ -1005,6 +1012,11 @@ run_tests_for_pipe(data_t *data, enum pipe p)
>>   		 * produce with an 8 bits per color framebuffer. */
>>   		igt_require(!IS_CHERRYVIEW(data->devid));
>>
>> +		/* Disable and let default luts be applied by kernel */
>> +		disable_degamma(primary->pipe);
>> +		disable_gamma(primary->pipe);
>> +		igt_display_commit(&data->display);
>> +
>>   		igt_assert(test_pipe_ctm(data, primary, red_green_blue,
>>   					 full_rgb, ctm));
>>   	}
>