lima: make fp16 render-targets opt-in with driconf

Lima can't do *both* FP16 *and* 4x MSAA at the same time. And because
GLES2 requires MAX_SAMPLES to be valid for *all* supported formats,
this means we can't support MSAA at all unless we disable support for
the FP16 formats when used as render-targets.

To allow applications that needs FP16 render-targets to still support
it, we introduce a driconf that makes the opposite trade; support FP16,
but not 4x MSAA. Unfortunately, we can't support both, and still be
following the spec.

Reviewed-by: Erico Nunes <nunes.erico@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35207>

docs/drivers/lima.rst

@@ -57,6 +57,14 @@ These are some display drivers that have been tested with Lima:
 - Tiny DRM: ``tinydrm``
 - Xilinx ZynqMP: ``zynqmp-dpsub``
 
+DRIconf variables
+-----------------
+
+``lima_allow_fp16_rts``
+   Expose support for FP16 render-targets. This has the side-effect of
+   dropping support for 4xMSAA, which unfortunately can't be supported
+   at the same time due to API and hardware restrictions.
+
 Environment variables
 ---------------------
 

src/gallium/drivers/lima/ci/lima-fails.txt

@@ -44,7 +44,6 @@ dEQP-GLES2.functional.texture.mipmap.cube.projected.linear_nearest,Fail
 
 wayland-dEQP-EGL.functional.create_context.no_config,Fail
 wayland-dEQP-EGL.functional.image.modify.renderbuffer_depth16_renderbuffer_clear_depth,Fail
-wayland-dEQP-EGL.functional.wide_color.window_fp16_default_colorspace,Fail
 wayland-dEQP-EGL.functional.wide_color.window_8888_colorspace_srgb,Fail
 wayland-dEQP-EGL.functional.wide_color.window_888_colorspace_srgb,Fail
 

src/gallium/drivers/lima/driinfo_lima.h

@@ -1 +1,4 @@
 /* lima specific driconf options */
+DRI_CONF_SECTION_MISCELLANEOUS
+   DRI_CONF_OPT_B(lima_allow_fp16_rts, false, "Allow using FP16 render-targets")
+DRI_CONF_SECTION_END

src/gallium/drivers/lima/lima_screen.c

@@ -246,9 +246,14 @@ lima_screen_is_format_supported(struct pipe_screen *pscreen,
       if (!lima_format_pixel_supported(format))
          return false;
 
-      /* multisample unsupported with half float target */
-      if (sample_count > 1 && util_format_is_float(format))
-         return false;
+      if (util_format_is_float(format)) {
+         if (!lima_screen(pscreen)->allow_fp16_rts)
+            return false;
+
+         /* multisample unsupported with half float target */
+         if (sample_count > 1)
+            return false;
+      }
    }
 
    if (usage & PIPE_BIND_DEPTH_STENCIL) {
@@ -589,6 +594,9 @@ lima_screen_create(int fd, const struct pipe_screen_config *config,
    driParseConfigFiles(config->options, config->options_info, 0,
                        "lima", NULL, NULL, NULL, 0, NULL, 0);
 
+   screen->allow_fp16_rts = driQueryOptionb(config->options,
+                                            "lima_allow_fp16_rts");
+
    if (!lima_screen_query_info(screen))
       goto err_out0;
 

src/gallium/drivers/lima/lima_screen.h

@@ -95,6 +95,7 @@ struct lima_screen {
    #define pp_buffer_size            0x1000
 
    bool has_growable_heap_buffer;
+   bool allow_fp16_rts;
 
    struct disk_cache *disk_cache;
 };