arc: check caches existence before use

Some cache operations ({i|d}cache_{enable|disable|status} or
flush_dcache_all) are built and used even if CONFIG_SYS_{I|D}CACHE_OFF
is set.

This is required for force disable of caches on early boot.
What if something was executed before U-boot and enabled caches
(low-level bootloaders, previously run kernel etc.)?

But if CPU doesn't really have caches any attempt to access
cache-related AUX registers triggers instruction error exception.

So for convenience we'll try to avoid exceptions by checking if CPU
actually has caches (we check separately data and instruction cache
existence) at all.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Igor Guryanov <guryanov@synopsys.com>

arch/arc/cpu/arc700/cache.c

@@ -14,21 +14,34 @@
 #define DC_CTRL_CACHE_DISABLE	(1 << 0)
 #define DC_CTRL_INV_MODE_FLUSH	(1 << 6)
 #define DC_CTRL_FLUSH_STATUS	(1 << 8)
+#define CACHE_VER_NUM_MASK	0xF
 
 int icache_status(void)
 {
+	/* If no cache in CPU exit immediately */
+	if (!(read_aux_reg(ARC_BCR_IC_BUILD) & CACHE_VER_NUM_MASK))
+		return 0;
+
 	return (read_aux_reg(ARC_AUX_IC_CTRL) & IC_CTRL_CACHE_DISABLE) !=
 	       IC_CTRL_CACHE_DISABLE;
 }
 
 void icache_enable(void)
 {
+	/* If no cache in CPU exit immediately */
+	if (!(read_aux_reg(ARC_BCR_IC_BUILD) & CACHE_VER_NUM_MASK))
+		return;
+
 	write_aux_reg(ARC_AUX_IC_CTRL, read_aux_reg(ARC_AUX_IC_CTRL) &
 		      ~IC_CTRL_CACHE_DISABLE);
 }
 
 void icache_disable(void)
 {
+	/* If no cache in CPU exit immediately */
+	if (!(read_aux_reg(ARC_BCR_IC_BUILD) & CACHE_VER_NUM_MASK))
+		return;
+
 	write_aux_reg(ARC_AUX_IC_CTRL, read_aux_reg(ARC_AUX_IC_CTRL) |
 		      IC_CTRL_CACHE_DISABLE);
 }
@@ -43,24 +56,40 @@ void invalidate_icache_all(void)
 
 int dcache_status(void)
 {
+	/* If no cache in CPU exit immediately */
+	if (!(read_aux_reg(ARC_BCR_DC_BUILD) & CACHE_VER_NUM_MASK))
+		return 0;
+
 	return (read_aux_reg(ARC_AUX_DC_CTRL) & DC_CTRL_CACHE_DISABLE) !=
 		DC_CTRL_CACHE_DISABLE;
 }
 
 void dcache_enable(void)
 {
+	/* If no cache in CPU exit immediately */
+	if (!(read_aux_reg(ARC_BCR_DC_BUILD) & CACHE_VER_NUM_MASK))
+		return;
+
 	write_aux_reg(ARC_AUX_DC_CTRL, read_aux_reg(ARC_AUX_DC_CTRL) &
 		      ~(DC_CTRL_INV_MODE_FLUSH | DC_CTRL_CACHE_DISABLE));
 }
 
 void dcache_disable(void)
 {
+	/* If no cache in CPU exit immediately */
+	if (!(read_aux_reg(ARC_BCR_DC_BUILD) & CACHE_VER_NUM_MASK))
+		return;
+
 	write_aux_reg(ARC_AUX_DC_CTRL, read_aux_reg(ARC_AUX_DC_CTRL) |
 		      DC_CTRL_CACHE_DISABLE);
 }
 
 void flush_dcache_all(void)
 {
+	/* If no cache in CPU exit immediately */
+	if (!(read_aux_reg(ARC_BCR_DC_BUILD) & CACHE_VER_NUM_MASK))
+		return;
+
 	/* Do flush of entire cache */
 	write_aux_reg(ARC_AUX_DC_FLSH, 1);
 

arch/arc/include/asm/arcregs.h

@@ -24,6 +24,7 @@
 #if (CONFIG_ARC_MMU_VER > 2)
 #define ARC_AUX_IC_PTAG		0x1E
 #endif
+#define ARC_BCR_IC_BUILD	0x77
 
 /* Timer related auxiliary registers */
 #define ARC_AUX_TIMER0_CNT	0x21	/* Timer 0 count */
@@ -42,6 +43,7 @@
 #if (CONFIG_ARC_MMU_VER > 2)
 #define ARC_AUX_DC_PTAG		0x5C
 #endif
+#define ARC_BCR_DC_BUILD	0x72
 
 #ifndef __ASSEMBLY__
 /* Accessors for auxiliary registers */