On Fri, Dec 22, 2017 at 08:34:47PM +0530, Uma Shankar wrote:
> From: Johnson Lin <johnson.lin@xxxxxxxxx>
>
> Some panels support limited range output (16-235) compared
> to full range RGB values (0-255). Also userspace can control
> the RGB range using "Broadcast RGB" property. Currently the
> code to handle full range to limited range is broken. This
> patch fixes the same by properly scaling down all the full
> range co-efficients with limited range scaling factor.
>
> Signed-off-by: Johnson Lin <johnson.lin@xxxxxxxxx>
> Signed-off-by: Uma Shankar <uma.shankar@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_color.c | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_color.c b/drivers/gpu/drm/i915/intel_color.c
> index aa66e95..777ce26 100644
> --- a/drivers/gpu/drm/i915/intel_color.c
> +++ b/drivers/gpu/drm/i915/intel_color.c
> @@ -94,16 +94,24 @@ static void ctm_mult_by_limited(uint64_t *result, int64_t *input)
> for (i = 0; i < 9; i++)
> result[i] = 0;
This can go.
>
> - for (i = 0; i < 3; i++) {
> - int64_t user_coeff = input[i * 3 + i];
> + for (i = 0; i < 9; i++) {
> + int64_t user_coeff = input[i];
That's not a two's complement number so should probably be u64.
> uint64_t limited_coeff = CTM_COEFF_LIMITED_RANGE >> 2;
> uint64_t abs_coeff = clamp_val(CTM_COEFF_ABS(user_coeff),
> 0,
> CTM_COEFF_4_0 - 1) >> 2;
Seems to me that we should be able to drop the >>2 from the limited_coeff
since it's always < 1.0, make both of these u32 and then use
'mul_u32_u32() >> 30' to get the answer.
>
> - result[i * 3 + i] = (limited_coeff * abs_coeff) >> 27;
> + /*
> + * By scaling every co-efficient with limited range (235-16)
> + * vs full range (0-255) the final o/p will be scaled down to
> + * fit in the limited range supported by the panel.
> + * Need to shift the multiplication result by 28 as the floating
> + * count expected is of 32bits, multiplication here is done in
> + * U2.30 so result need to be right shifted by 60-32 = 28
> + */
> + result[i] = (limited_coeff * abs_coeff) >> 28;
> if (CTM_COEFF_NEGATIVE(user_coeff))
And this can be replaced with just
result[i] |= user_coeff & CTM_COEFF_SIGN;
to eliminate the silly branch.
> - result[i * 3 + i] |= CTM_COEFF_SIGN;
> + result[i] |= CTM_COEFF_SIGN;
> }
> }
>
> --
> 1.7.9.5
>
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--
Ville Syrjälä
Intel OTC
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