mtrr: Define a function for obtaining free var mtrr
Instead of hard-coding var mtrr numbers in code, use this function to
identify the first available variable mtrr. If no such mtrr is
available, the function will return -1.
Change-Id: I2a1e02cdb45c0ab7e30609641977471eaa2431fd
Signed-off-by: Furquan Shaikh <furquan@google.com>
Reviewed-on: https://review.coreboot.org/14115
Tested-by: build bot (Jenkins)
Reviewed-by: Andrey Petrov <andrey.petrov@intel.com>
diff --git a/src/cpu/x86/mtrr/earlymtrr.c b/src/cpu/x86/mtrr/earlymtrr.c
index a84ecf8..eae6ba6 100644
--- a/src/cpu/x86/mtrr/earlymtrr.c
+++ b/src/cpu/x86/mtrr/earlymtrr.c
@@ -2,6 +2,30 @@
#include <cpu/x86/mtrr.h>
#include <cpu/x86/msr.h>
+/* Get first available variable MTRR.
+ * Returns var# if available, else returns -1.
+ */
+int get_free_var_mtrr(void)
+{
+ msr_t msr, maskm;
+ int vcnt;
+ int i;
+
+ /* Read MTRRCap and get vcnt - variable memory type ranges. */
+ msr = rdmsr(MTRR_CAP_MSR);
+ vcnt = msr.lo & 0xff;
+
+ /* Identify the first var mtrr which is not valid. */
+ for (i = 0; i < vcnt; i++) {
+ maskm = rdmsr(MTRR_PHYS_MASK(i));
+ if ((maskm.lo & MTRR_PHYS_MASK_VALID) == 0)
+ return i;
+ }
+
+ /* No free var mtrr. */
+ return -1;
+}
+
#ifdef __ROMCC__
static
#endif
diff --git a/src/include/cpu/x86/mtrr.h b/src/include/cpu/x86/mtrr.h
index d158735..4eb4f13 100644
--- a/src/include/cpu/x86/mtrr.h
+++ b/src/include/cpu/x86/mtrr.h
@@ -81,6 +81,7 @@
#if !defined(__ASSEMBLER__) && defined(__PRE_RAM__) && !defined(__ROMCC__)
void set_var_mtrr(unsigned reg, unsigned base, unsigned size, unsigned type);
+int get_free_var_mtrr(void);
#endif
/* Align up to next power of 2, suitable for ROMCC and assembler too.