amd/stoneyridge: Sync PSP base to MSR

According to AMD, there exists an undocumented MSR which must be
written with the PSP's base address.  Read the value from the PSP's
config space and sync each core's copy of the MSR to match.

BUG=b:76167350
TEST=boot Grunt and verify "rdrand: disabled" goes away from dmesg

Change-Id: I30027d3b0a6fbd540375e96001beb9c25bf3a678
Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/28608
Reviewed-by: Martin Roth <martinroth@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/amd/stoneyridge/cpu.c

@@ -121,6 +121,23 @@ static void model_15_init(struct device *dev)
 {
 	check_mca();
 	setup_lapic();
+
+	/*
+	 * Per AMD, sync an undocumented MSR with the PSP base address.
+	 * Experiments showed that if you write to the MSR after it has
+	 * been previously programmed, it causes a general protection fault.
+	 * Also, the MSR survives warm reset and S3 cycles, so we need to
+	 * test if it was previously written before writing to it.
+	 */
+	msr_t psp_msr;
+	uint32_t psp_bar; /* Note: NDA BKDG names this 32-bit register BAR3 */
+	psp_bar = pci_read_config32(SOC_PSP_DEV, PCI_BASE_ADDRESS_4);
+	psp_bar &= ~PCI_BASE_ADDRESS_MEM_ATTR_MASK;
+	psp_msr = rdmsr(0xc00110a2);
+	if (psp_msr.lo == 0) {
+		psp_msr.lo = psp_bar;
+		wrmsr(0xc00110a2, psp_msr);
+	}
 }
 
 static struct device_operations cpu_dev_ops = {