Add SoC specific microcode update check in ramstage

Some Intel SoCs which support SGX feature, report the
microcode patch revision one less than the actual revision.
This results in the same microcode patch getting loaded again.
Add a SoC specific check to avoid reloading the same patch.

BUG=chrome-os-partner:42046
BRANCH=None
TEST=Built for glados and tested on RVP3
CQ-DEPEND=CL:286054

Change-Id: Iab4c34c6c55119045947f598e89352867c67dcb8
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: ab2ed73db3581cd432f9bc84acca47f5e53a0e9b
Original-Change-Id: I4f7bf9c841e5800668208c11b0afcf8dba48a775
Original-Signed-off-by: Rizwan Qureshi <rizwan.qureshi@intel.com>
Original-Reviewed-on: https://chromium-review.googlesource.com/287513
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/11055
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)

src/cpu/intel/microcode/microcode.c

@@ -28,6 +28,7 @@
 #include <cpu/cpu.h>
 #include <cpu/x86/msr.h>
 #include <cpu/intel/microcode.h>
+#include <rules.h>
 
 #if !defined(__PRE_RAM__)
 #include <cbfs.h>
@@ -95,6 +96,14 @@ void intel_microcode_load_unlocked(const void *microcode_patch)
 	if (current_rev == m->rev)
 		return;
 
+#if ENV_RAMSTAGE
+	/*SoC specific check to update microcode*/
+	if (soc_skip_ucode_update(current_rev, m->rev)) {
+		printk(BIOS_DEBUG, "Skip microcode update\n");
+		return;
+	}
+#endif
+
 	msr.lo = (unsigned long)m + sizeof(struct microcode);
 	msr.hi = 0;
 	wrmsr(0x79, msr);
@@ -202,3 +211,10 @@ void intel_update_microcode_from_cbfs(void)
 	spin_unlock(&microcode_lock);
 #endif
 }
+
+#if ENV_RAMSTAGE
+__attribute__((weak)) int soc_skip_ucode_update(u32 currrent_patch_id, u32 new_patch_id)
+{
+	return 0;
+}
+#endif

src/include/cpu/intel/microcode.h

@@ -29,6 +29,10 @@ const void *intel_microcode_find(void);
  * well as ensuring the microcode matches the family and revision (i.e. with
  * intel_microcode_find()). */
 void intel_microcode_load_unlocked(const void *microcode_patch);
+
+/* SoC specific check to determine if microcode update is really
+ * required, will skip microcode update if true. */
+int soc_skip_ucode_update(u32 currrent_patch_id, u32 new_patch_id);
 #endif
 
 #endif