gallium: add a sampler reduction cap + settings

This is to allow for
  VK_EXT_sampler_filter_minmax
  GL_EXT_texture_filter_minmax
support

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9487>

docs/gallium/screen.rst

@@ -612,6 +612,7 @@ The integer capabilities:
 * ``PIPE_CAP_PREFER_REAL_BUFFER_IN_CONSTBUF0``: The state tracker is encouraged to upload constants into a real buffer and bind it into constant buffer 0 instead of binding a user pointer. This may enable a faster codepath in a gallium frontend for drivers that really prefer a real buffer.
 * ``PIPE_CAP_GL_CLAMP``: Driver natively supports GL_CLAMP.  Required for non-NIR drivers with the GL frontend.  NIR drivers with the cap unavailable will have GL_CLAMP lowered to txd/txl with a saturate on the coordinates.
 * ``PIPE_CAP_TEXRECT``: Driver supports rectangle textures.  Required for OpenGL on `!prefers_nir` drivers.  If this cap is not present, st/mesa will lower the NIR to use normal 2D texture sampling by using either `txs` or `nir_intrinsic_load_texture_scaling` to normalize the texture coordinates.
+* ``PIPE_CAP_SAMPLER_REDUCTION_MINMAX``: Driver support min/max sampler reduction.
 
 .. _pipe_capf:
 

src/gallium/auxiliary/util/u_screen.c

@@ -459,6 +459,9 @@ u_pipe_screen_get_param_defaults(struct pipe_screen *pscreen,
    case PIPE_CAP_SHADER_ATOMIC_INT64:
       return 0;
 
+   case PIPE_CAP_SAMPLER_REDUCTION_MINMAX:
+      return 0;
+
    default:
       unreachable("bad PIPE_CAP_*");
    }

src/gallium/include/pipe/p_defines.h

@@ -210,6 +210,12 @@ enum pipe_tex_compare {
    PIPE_TEX_COMPARE_R_TO_TEXTURE,
 };
 
+enum pipe_tex_reduction_mode {
+   PIPE_TEX_REDUCTION_WEIGHTED_AVERAGE,
+   PIPE_TEX_REDUCTION_MIN,
+   PIPE_TEX_REDUCTION_MAX,
+};
+
 /**
  * Clear buffer bits
  */
@@ -979,6 +985,7 @@ enum pipe_cap
    PIPE_CAP_PREFER_REAL_BUFFER_IN_CONSTBUF0,
    PIPE_CAP_GL_CLAMP,
    PIPE_CAP_TEXRECT,
+   PIPE_CAP_SAMPLER_REDUCTION_MINMAX,
 
    PIPE_CAP_LAST,
    /* XXX do not add caps after PIPE_CAP_LAST! */

src/gallium/include/pipe/p_state.h

@@ -413,6 +413,7 @@ struct pipe_sampler_state
    unsigned max_anisotropy:5;
    unsigned seamless_cube_map:1;
    unsigned border_color_is_integer:1;
+   unsigned reduction_mode:2;    /**< PIPE_TEX_REDUCTION_x */
    float lod_bias;               /**< LOD/lambda bias */
    float min_lod, max_lod;       /**< LOD clamp range, after bias */
    union pipe_color_union border_color;