etnaviv: fix flatshading on halti5 GPUs

Halti5 has no interpolation setting which will take into account the
rasterizer flatshade state. Force the interpolation qualifier to flatshade
for the color varyings when API level flatshade is enabled. Only set the
new bit in the shader key on halti5 GPUs to avoid generating unnecessary
shader variants on GPUs where the rasterizer flatshade state is properly
applied to the varyings.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Christian Gmeiner <cgmeiner@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/32991>

src/gallium/drivers/etnaviv/etnaviv_compiler_nir.c

@@ -1222,6 +1222,11 @@ etna_compile_shader(struct etna_shader_variant *v)
          unsigned idx = var->data.driver_location;
          sf->reg[idx].reg = idx + 1;
          sf->reg[idx].slot = var->data.location;
+         if (var->data.interpolation == INTERP_MODE_NONE && v->key.flatshade &&
+             (var->data.location == VARYING_SLOT_COL0 ||
+              var->data.location == VARYING_SLOT_COL1)) {
+            var->data.interpolation = INTERP_MODE_FLAT;
+         }
          sf->reg[idx].interpolation = var->data.interpolation;
          sf->reg[idx].num_components = glsl_get_components(var->type);
          sf->num_reg = MAX2(sf->num_reg, idx+1);

src/gallium/drivers/etnaviv/etnaviv_context.c

@@ -302,6 +302,9 @@ etna_draw_vbo(struct pipe_context *pctx, const struct pipe_draw_info *info,
       .sprite_coord_yinvert = !!ctx->rasterizer->sprite_coord_mode,
    };
 
+   if (screen->info->halti >= 5)
+      key.flatshade = ctx->rasterizer->flatshade;
+
     for (i = 0; i < pfb->nr_cbufs; i++) {
        if (pfb->cbufs[i])
          key.frag_rb_swap |= !!translate_pe_format_rb_swap(pfb->cbufs[i]->format) << i;

src/gallium/drivers/etnaviv/etnaviv_shader.h

@@ -55,6 +55,8 @@ struct etna_shader_key
          unsigned sprite_coord_yinvert : 1;
          /* do we need to lower sample_tex_compare */
          unsigned has_sample_tex_compare : 1;
+         /* color varyings should be flat shaded */
+         unsigned flatshade : 1;
       };
       uint32_t global;
    };