Re: [PATCH i-g-t 1/2] test/kms_color: Clamp CTM values to -2.0~2.0 for MediaTek devices

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Jan 30, 2026 at 01:32:05PM +0000, Jason-JH Lin (林睿祥) wrote:
> On Thu, 2026-01-29 at 13:15 +0200, Ville Syrjälä wrote:
> > On Wed, Jan 28, 2026 at 04:24:42PM +0800, Jason-JH Lin wrote:
> > > Use clamp to restrict CTM matrix values to the -2.0 to 2.0 range
> > > for
> > > MediaTek devices, ensuring tests do not exceed hardware limits.
> > > 
> > > Signed-off-by: Jason-JH Lin <jason-jh.lin@mediatek.com>
> > > ---
> > >  tests/kms_color.c | 19 +++++++++++++++++--
> > >  1 file changed, 17 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/tests/kms_color.c b/tests/kms_color.c
> > > index b2ca6975d6a5..c6cd35d74a2f 100644
> > > --- a/tests/kms_color.c
> > > +++ b/tests/kms_color.c
> > > @@ -76,6 +76,8 @@
> > >   * @gamma-lut:          Gamma LUT
> > >   */
> > >  
> > > +#define CTM_SIZE		(9)
> > > +
> > >  IGT_TEST_DESCRIPTION("Test Color Features at Pipe level");
> > >  
> > >  static bool test_pipe_degamma(data_t *data,
> > > @@ -1025,7 +1027,7 @@ run_tests_for_pipe(data_t *data)
> > >  		const char *name;
> > >  		int iter;
> > >  		const color_t *fb_colors;
> > > -		double ctm[9];
> > > +		double ctm[CTM_SIZE];
> > >  		const char *desc;
> > >  	} ctm_tests[] = {
> > >  		{ .name = "ctm-red-to-blue",
> > > @@ -1128,6 +1130,19 @@ run_tests_for_pipe(data_t *data)
> > >  	}
> > >  
> > >  	for (i = 0; i < ARRAY_SIZE(ctm_tests); i++) {
> > > +		double fixed_ctm[CTM_SIZE];
> > > +		const double *ctm_ptr = ctm_tests[i].ctm;
> > > +
> > > +		/* The valid value of MediaTek color matrix range
> > > is -2.0 ~ 2.0 */
> > > +		if (is_mtk_device(data->drm_fd)) {
> > > +			int j;
> > > +
> > > +			for (j = 0; j < CTM_SIZE; j++)
> > > +				fixed_ctm[j] =
> > > clamp(ctm_tests[i].ctm[j], -2.0, 2.0);
> > > +
> > > +			ctm_ptr = fixed_ctm;
> > > +		}
> > 
> > The kernel is supposed to clamp this.
> 
> Thanks for the reviews!
> 
> The reason I added the clamp in here is that, without it, IGT will
> generate a reference framebuffer using CTM=100.0 on the CPU side, then
> send CTM1.0 to kernel.
> IGT will generate another framebuffer using CTM=1.0, then send
> CTM=100.0 to the kernel.
> 
> The kernel will clamp the CTM from 100.0 to 2.0 due to hardware limits,
> so the hardware output will not match the CPU-generated reference,
> resulting in a CRC mismatch and a test failure.
> 
> Therefore, I think I need to clamp CTM from 100.0 to 2.0 before IGT
> generating a reference framebuffer on CPU side.

IIRC the way the test does things is that with the 100.0 (or
whatever >1.0) the colors should end up fully saturated anyway.
So whether it used 2.0 or 100.0 shouldn't matter.

-- 
Ville Syrjälä
Intel