x86: Test mtrr support flag before accessing mtrr msr

On some x86 processors (like Intel Quark) the MTRR registers are not
supported. This is reflected by the CPUID (EAX 01H) result EDX[12].
Accessing the MTRR registers on such processors will cause #GP so we
must test the support flag before accessing MTRR MSRs.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>

arch/x86/cpu/mtrr.c

@@ -22,6 +22,9 @@ DECLARE_GLOBAL_DATA_PTR;
 /* Prepare to adjust MTRRs */
 void mtrr_open(struct mtrr_state *state)
 {
+	if (!gd->arch.has_mtrr)
+		return;
+
 	state->enable_cache = dcache_status();
 
 	if (state->enable_cache)
@@ -33,6 +36,9 @@ void mtrr_open(struct mtrr_state *state)
 /* Clean up after adjusting MTRRs, and enable them */
 void mtrr_close(struct mtrr_state *state)
 {
+	if (!gd->arch.has_mtrr)
+		return;
+
 	wrmsrl(MTRR_DEF_TYPE_MSR, state->deftype | MTRR_DEF_TYPE_EN);
 	if (state->enable_cache)
 		enable_caches();
@@ -45,6 +51,9 @@ int mtrr_commit(bool do_caches)
 	uint64_t mask;
 	int i;
 
+	if (!gd->arch.has_mtrr)
+		return -ENOSYS;
+
 	mtrr_open(&state);
 	for (i = 0; i < gd->arch.mtrr_req_count; i++, req++) {
 		mask = ~(req->size - 1);
@@ -66,6 +75,9 @@ int mtrr_add_request(int type, uint64_t start, uint64_t size)
 	struct mtrr_request *req;
 	uint64_t mask;
 
+	if (!gd->arch.has_mtrr)
+		return -ENOSYS;
+
 	if (gd->arch.mtrr_req_count == MAX_MTRR_REQUESTS)
 		return -ENOSPC;
 	req = &gd->arch.mtrr_req[gd->arch.mtrr_req_count++];

arch/x86/include/asm/mtrr.h

@@ -65,7 +65,6 @@ void mtrr_open(struct mtrr_state *state);
  *
  * @state:	Structure from mtrr_open()
  */
-/*  */
 void mtrr_close(struct mtrr_state *state);
 
 /**
@@ -76,6 +75,8 @@ void mtrr_close(struct mtrr_state *state);
  * @type:	Requested type (MTRR_TYPE_)
  * @start:	Start address
  * @size:	Size
+ *
+ * @return:	0 on success, non-zero on failure
  */
 int mtrr_add_request(int type, uint64_t start, uint64_t size);
 
@@ -86,6 +87,8 @@ int mtrr_add_request(int type, uint64_t start, uint64_t size);
  * It must be called with caches disabled.
  *
  * @do_caches:	true if caches are currently on
+ *
+ * @return:	0 on success, non-zero on failure
  */
 int mtrr_commit(bool do_caches);
 

arch/x86/lib/init_helpers.c

@@ -7,6 +7,7 @@
 #include <common.h>
 #include <fdtdec.h>
 #include <spi.h>
+#include <asm/errno.h>
 #include <asm/mtrr.h>
 #include <asm/sections.h>
 
@@ -71,7 +72,8 @@ int init_cache_f_r(void)
 	int ret;
 
 	ret = mtrr_commit(false);
-	if (ret)
+	/* If MTRR MSR is not implemented by the processor, just ignore it */
+	if (ret && ret != -ENOSYS)
 		return ret;
 #endif
 	/* Initialise the CPU cache(s) */