cpu/amd/fam10h-15h: Add tsc_freq_mhz() function

The AMD Family 10h/15h processors use a TSC that increments at
the P0 core frequency.  Allow coreboot to query the TSC frequency.

Change-Id: I73ead4fd4af18991452d59985b667a54689778cd
Signed-off-by: Timothy Pearson <tpearson@raptorengineeringinc.com>
Reviewed-on: https://review.coreboot.org/12834
Tested-by: build bot (Jenkins)
Tested-by: Raptor Engineering Automated Test Stand <noreply@raptorengineeringinc.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/cpu/amd/family_10h-family_15h/Makefile.inc

@@ -3,6 +3,8 @@ ramstage-y += model_10xxx_init.c
 ramstage-y += processor_name.c
 
 romstage-y += update_microcode.c
+romstage-y += tsc_freq.c
+ramstage-y += tsc_freq.c
 romstage-y += ram_calc.c
 ramstage-y += ram_calc.c
 ramstage-y += monotonic_timer.c

src/cpu/amd/family_10h-family_15h/tsc_freq.c

@@ -0,0 +1,37 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright (C) 2016 Raptor Engineering
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <stdint.h>
+#include <cpu/x86/msr.h>
+#include <cpu/x86/tsc.h>
+
+unsigned long tsc_freq_mhz(void)
+{
+	msr_t msr;
+	uint8_t cpufid;
+	uint8_t cpudid;
+
+	/* On Family 10h/15h CPUs the TSC increments
+         * at the P0 clock rate.  Read the P0 clock
+         * frequency from the P0 MSR and convert
+         * to MHz.  See also the Family 15h BKDG
+         * Rev. 3.14 page 569.
+         */
+	msr = rdmsr(0xc0010064);
+	cpufid = (msr.lo & 0x3f);
+	cpudid = (msr.lo & 0x1c0) >> 6;
+
+	return (100 * (cpufid + 0x10)) / (0x01 << cpudid);
+}