amdgpu: add parameter to force write-combine memory

Author: pepijndevos

drivers/gpu/drm/Kconfig

@@ -31,6 +31,16 @@ menuconfig DRM
 
 if DRM
 
+config DRM_ARCH_CAN_WC
+    bool "Force Architecture can write-combine memory"
+    depends on DRM
+    default n
+    help
+      Enables write-combining even if it is not enabled by default.
+      Only use if the target systems support write-combining on
+      the memory used by the graphics adapters.
+      If in doubt, say 'N'
+
 config DRM_MIPI_DBI
 	tristate
 	depends on DRM

include/drm/drm_cache.h

@@ -45,6 +45,9 @@ bool drm_need_swiotlb(int dma_bits);
 
 static inline bool drm_arch_can_wc_memory(void)
 {
+#if defined(CONFIG_DRM_ARCH_CAN_WC)
+	return true;
+#endif
 #if defined(CONFIG_PPC) && !defined(CONFIG_NOT_COHERENT_CACHE)
 	return false;
 #elif defined(CONFIG_MIPS) && defined(CONFIG_CPU_LOONGSON64)