From: Jeff Hansen <jhansen@cardaccess-inc.com>
Subject: [PATCH] kmap_coherent

On ASUS WL-500gP there are some "Data bus error"s when executing simple
commands liks "ps" or "cat /proc/1/cmdline".

This fixes OpenWrt ticket #1485: https://dev.openwrt.org/ticket/1485
---
--- a/arch/mips/include/asm/cpu-features.h
+++ b/arch/mips/include/asm/cpu-features.h
@@ -243,6 +243,9 @@
 #ifndef cpu_has_pindexed_dcache
 #define cpu_has_pindexed_dcache	(cpu_data[0].dcache.flags & MIPS_CACHE_PINDEX)
 #endif
+#ifndef cpu_use_kmap_coherent
+#define cpu_use_kmap_coherent 1
+#endif
 
 /*
  * I-Cache snoops remote store.	 This only matters on SMP.  Some multiprocessors
--- a/arch/mips/include/asm/mach-bcm47xx/cpu-feature-overrides.h
+++ b/arch/mips/include/asm/mach-bcm47xx/cpu-feature-overrides.h
@@ -80,4 +80,6 @@
 #define cpu_scache_line_size()		0
 #define cpu_has_vz			0
 
+#define cpu_use_kmap_coherent		0
+
 #endif /* __ASM_MACH_BCM47XX_CPU_FEATURE_OVERRIDES_H */
--- a/arch/mips/mm/c-r4k.c
+++ b/arch/mips/mm/c-r4k.c
@@ -697,7 +697,7 @@ static inline void local_r4k_flush_cache
 		map_coherent = (cpu_has_dc_aliases &&
 				page_mapcount(page) &&
 				!Page_dcache_dirty(page));
-		if (map_coherent)
+		if (map_coherent && cpu_use_kmap_coherent)
 			vaddr = kmap_coherent(page, addr);
 		else
 			vaddr = kmap_atomic(page);
@@ -719,7 +719,7 @@ static inline void local_r4k_flush_cache
 	}
 
 	if (vaddr) {
-		if (map_coherent)
+		if (map_coherent && cpu_use_kmap_coherent)
 			kunmap_coherent();
 		else
 			kunmap_atomic(vaddr);
--- a/arch/mips/mm/init.c
+++ b/arch/mips/mm/init.c
@@ -174,7 +174,7 @@ void copy_user_highpage(struct page *to,
 	void *vfrom, *vto;
 
 	vto = kmap_atomic(to);
-	if (cpu_has_dc_aliases &&
+	if (cpu_has_dc_aliases && cpu_use_kmap_coherent &&
 	    page_mapcount(from) && !Page_dcache_dirty(from)) {
 		vfrom = kmap_coherent(from, vaddr);
 		copy_page(vto, vfrom);
@@ -196,7 +196,7 @@ void copy_to_user_page(struct vm_area_st
 	struct page *page, unsigned long vaddr, void *dst, const void *src,
 	unsigned long len)
 {
-	if (cpu_has_dc_aliases &&
+	if (cpu_has_dc_aliases && cpu_use_kmap_coherent &&
 	    page_mapcount(page) && !Page_dcache_dirty(page)) {
 		void *vto = kmap_coherent(page, vaddr) + (vaddr & ~PAGE_MASK);
 		memcpy(vto, src, len);
@@ -214,7 +214,7 @@ void copy_from_user_page(struct vm_area_
 	struct page *page, unsigned long vaddr, void *dst, const void *src,
 	unsigned long len)
 {
-	if (cpu_has_dc_aliases &&
+	if (cpu_has_dc_aliases && cpu_use_kmap_coherent &&
 	    page_mapcount(page) && !Page_dcache_dirty(page)) {
 		void *vfrom = kmap_coherent(page, vaddr) + (vaddr & ~PAGE_MASK);
 		memcpy(dst, vfrom, len);