radv: fix determining the maximum number of waves that can use scratch

This estimation was incorrect, the number of waves doesn't only
depend of the number of VGPRs.
Though, {SPI,COMPUTE}_TMPRING_SIZE.WAVES should limit the number of
scratch waves in flight, not sure if limiting it really works.

This fixes a GPU hang with an upcoming game, and this might also
helps resolving some spurious random GPU hangs.

Cc: mesa-stable
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12700>

src/amd/vulkan/radv_pipeline.c

@@ -254,7 +254,7 @@ radv_pipeline_init_scratch(const struct radv_device *device, struct radv_pipelin
 
          max_stage_waves =
             MIN2(max_stage_waves, 4 * device->physical_device->rad_info.num_good_compute_units *
-                                     (256 / pipeline->shaders[i]->config.num_vgprs));
+                 radv_get_max_waves(device, pipeline->shaders[i], i));
          max_waves = MAX2(max_waves, max_stage_waves);
       }
    }

src/amd/vulkan/radv_shader.c

@@ -1737,7 +1737,7 @@ radv_get_shader_name(struct radv_shader_info *info, gl_shader_stage stage)
 }
 
 unsigned
-radv_get_max_waves(struct radv_device *device, struct radv_shader_variant *variant,
+radv_get_max_waves(const struct radv_device *device, struct radv_shader_variant *variant,
                    gl_shader_stage stage)
 {
    struct radeon_info *info = &device->physical_device->rad_info;

src/amd/vulkan/radv_shader.h

@@ -470,7 +470,7 @@ struct radv_shader_variant *radv_create_trap_handler_shader(struct radv_device *
 
 void radv_shader_variant_destroy(struct radv_device *device, struct radv_shader_variant *variant);
 
-unsigned radv_get_max_waves(struct radv_device *device, struct radv_shader_variant *variant,
+unsigned radv_get_max_waves(const struct radv_device *device, struct radv_shader_variant *variant,
                             gl_shader_stage stage);
 
 const char *radv_get_shader_name(struct radv_shader_info *info, gl_shader_stage stage);