[Intel-gfx] [PATCH 2/3] drm/intel: Attempt to use 10-bit gamma palette mode

[Andrew Lutomirski]

Should this patch be enough to output 10 bits/channel on a digital
output?  I just ordered some 10-bit monitors and it would be fun to
use them in all their high-precision glory?

It should be relatively easy to use spotread (from Argyll) along with
some hacked-up gamma loader to verify that it's working.

--Andy

On Mon, Apr 26, 2010 at 6:24 PM, Peter Clifton <pcjc2 at cam.ac.uk> wrote:
> ---
>  drivers/gpu/drm/i915/i915_reg.h      |    7 ++++++-
>  drivers/gpu/drm/i915/intel_display.c |   33 ++++++++++++++++++++++++++-------
>  2 files changed, 32 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> index ab1bd2d..7a0c6ac 100644
> --- a/drivers/gpu/drm/i915/i915_reg.h
> +++ b/drivers/gpu/drm/i915/i915_reg.h
> @@ -1766,6 +1766,9 @@
>  #define   PIPECONF_INTERLACE_W_FIELD_INDICATION        (6 << 21)
>  #define   PIPECONF_INTERLACE_FIELD_0_ONLY              (7 << 21)
>  #define   PIPECONF_CXSR_DOWNCLOCK      (1<<16)
> +#define PIPEAGCMAXRED          0x70010
> +#define PIPEAGCMAXGREEN                0x70014
> +#define PIPEAGCMAXBLUE         0x70018
>  #define PIPEASTAT              0x70024
>  #define   PIPE_FIFO_UNDERRUN_STATUS            (1UL<<31)
>  #define   PIPE_CRC_ERROR_ENABLE                        (1UL<<29)
> @@ -1958,13 +1961,15 @@
>  /* Pipe B */
>  #define PIPEBDSL               0x71000
>  #define PIPEBCONF              0x71008
> +#define PIPEBGCMAXRED          0x71010
> +#define PIPEBGCMAXGREEN                0x71014
> +#define PIPEBGCMAXBLUE         0x71018
>  #define PIPEBSTAT              0x71024
>  #define PIPEBFRAMEHIGH         0x71040
>  #define PIPEBFRAMEPIXEL                0x71044
>  #define PIPEB_FRMCOUNT_GM45    0x71040
>  #define PIPEB_FLIPCOUNT_GM45   0x71044
>
> -
>  /* Display B control */
>  #define DSPBCNTR               0x71180
>  #define   DISPPLANE_ALPHA_TRANS_ENABLE         (1<<15)
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 456f738..5e8191a 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -3433,6 +3433,9 @@ void intel_crtc_load_lut(struct drm_crtc *crtc)
>        int pipe = intel_crtc->pipe;
>        int pal_reg = (pipe == 0) ? PALETTE_A : PALETTE_B;
>        int pipeconf_reg = (pipe == 0) ? PIPEACONF : PIPEBCONF;
> +       int maxr_reg = (pipe == 0) ? PIPEAGCMAXRED : PIPEBGCMAXRED;
> +       int maxg_reg = (pipe == 0) ? PIPEAGCMAXGREEN : PIPEBGCMAXGREEN;
> +       int maxb_reg = (pipe == 0) ? PIPEAGCMAXBLUE : PIPEBGCMAXBLUE;
>        int pipeconf = I915_READ(pipeconf_reg);
>        int i;
>
> @@ -3445,17 +3448,33 @@ void intel_crtc_load_lut(struct drm_crtc *crtc)
>                pal_reg = (intel_crtc->pipe == 0) ? LGC_PALETTE_A :
>                                                    LGC_PALETTE_B;
>
> -       /* Switch to 8-bit gamma mode */
> -       pipeconf &= ~PIPEACONF_GAMMA;
> +       /* Switch to 10-bit gamma mode */
> +       pipeconf |= PIPEACONF_GAMMA;
>        I915_WRITE(pipeconf_reg, pipeconf);
>        I915_READ(pipeconf_reg);
>
> -       for (i = 0; i < 256; i++) {
> -               I915_WRITE(pal_reg + 4 * i,
> -                          ((intel_crtc->lut_r[i] >> 8) << 16) |
> -                          ((intel_crtc->lut_g[i] >> 8) << 8) |
> -                          (intel_crtc->lut_b[i] >> 8));
> +       /* Use every other value from the LUT passed,
> +        * 10-bit mode uses 128 entries. */
> +       for (i = 0; i < 128; i++) {
> +               I915_WRITE(pal_reg + 8 * i,
> +                          ((intel_crtc->lut_r[2 * i] & 0xFF) << 16) |
> +                          ((intel_crtc->lut_g[2 * i] & 0xFF) << 8) |
> +                          (intel_crtc->lut_b[2 * i] & 0xFF));
> +               I915_WRITE(pal_reg + 8 * i + 4,
> +                          ((intel_crtc->lut_r[2 * i] >> 8) << 16) |
> +                          ((intel_crtc->lut_g[2 * i] >> 8) << 8) |
> +                          (intel_crtc->lut_b[2 * i] >> 8));
>        }
> +
> +       /* FIXME: Distortion here, we're trying to get 129 evenly spaced
> +        * samples from a LUT with 256 entries. We use 0, 2, 4 ... 254,
> +        * for the main palette, then entry 255 for this last register.
> +        */
> +       /* Note that these registers _could_ take the LUT value of
> +        * 1024, but we're maxing out at 1023.984375 as it is easier. */
> +       I915_WRITE(maxr_reg, intel_crtc->lut_r[255]);
> +       I915_WRITE(maxg_reg, intel_crtc->lut_g[255]);
> +       I915_WRITE(maxb_reg, intel_crtc->lut_b[255]);
>  }
>
>  static int intel_crtc_cursor_set(struct drm_crtc *crtc,
> --
> 1.7.0.4
>
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