gallium: Add PIPE_CAP_FBFETCH_COHERENT and expose extensions

st/mesa now exposes KHR_blend_equation_advanced_coherent and
EXT_shader_framebuffer_fetch if the new capability is supported.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/gallium/auxiliary/util/u_screen.c

@@ -271,6 +271,7 @@ u_pipe_screen_get_param_defaults(struct pipe_screen *pscreen,
       return 0;
 
    case PIPE_CAP_FBFETCH:
+   case PIPE_CAP_FBFETCH_COHERENT:
    case PIPE_CAP_TGSI_MUL_ZERO_WINS:
    case PIPE_CAP_DOUBLES:
    case PIPE_CAP_INT64:

src/gallium/docs/source/screen.rst

@@ -382,6 +382,8 @@ The integer capabilities:
   current framebuffer can be read in the shader.  0 means framebuffer fetch
   is not supported.  1 means that only the first render target can be read,
   and a larger value would mean that multiple render targets are supported.
+* ``PIPE_CAP_FBFETCH_COHERENT``: Whether framebuffer fetches from the fragment
+  shader can be guaranteed to be coherent with framebuffer writes.
 * ``PIPE_CAP_TGSI_MUL_ZERO_WINS``: Whether TGSI shaders support the
   ``TGSI_PROPERTY_MUL_ZERO_WINS`` shader property.
 * ``PIPE_CAP_DOUBLES``: Whether double precision floating-point operations

src/gallium/include/pipe/p_defines.h

@@ -884,6 +884,7 @@ enum pipe_cap
    PIPE_CAP_DMABUF,
    PIPE_CAP_PREFER_COMPUTE_BLIT_FOR_MULTIMEDIA,
    PIPE_CAP_FRAGMENT_SHADER_INTERLOCK,
+   PIPE_CAP_FBFETCH_COHERENT,
 };
 
 /**

src/mesa/state_tracker/st_extensions.c

@@ -1395,13 +1395,17 @@ void st_init_extensions(struct pipe_screen *screen,
    }
 
    unsigned max_fb_fetch_rts = screen->get_param(screen, PIPE_CAP_FBFETCH);
+   bool coherent_fb_fetch =
+      screen->get_param(screen, PIPE_CAP_FBFETCH_COHERENT);
 
    if (max_fb_fetch_rts > 0) {
       extensions->KHR_blend_equation_advanced = true;
+      extensions->KHR_blend_equation_advanced_coherent = coherent_fb_fetch;
 
       if (max_fb_fetch_rts >=
           screen->get_param(screen, PIPE_CAP_MAX_RENDER_TARGETS)) {
          extensions->EXT_shader_framebuffer_fetch_non_coherent = true;
+         extensions->EXT_shader_framebuffer_fetch = coherent_fb_fetch;
       }
    }