soc/amd/common/block/smn: add smn_read64

Add smn_read64 which calls smn_read32 twice to read two adjacent 32 bit
SMN registers and merges the results into a 64 bit value which it then
returns.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: Ib2d58ec9818559cbefd7b819ae311ad02fafa18f
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76552
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>

src/soc/amd/common/block/include/amdblocks/smn.h

@@ -6,6 +6,7 @@
 #include <types.h>
 
 uint32_t smn_read32(uint32_t reg);
+uint64_t smn_read64(uint32_t reg);
 void smn_write32(uint32_t reg, uint32_t val);
 
 #endif /* AMD_BLOCK_SMN_H */

src/soc/amd/common/block/smn/smn.c

@@ -15,6 +15,11 @@ uint32_t smn_read32(uint32_t reg)
 	return pci_read_config32(SOC_GNB_DEV, SMN_DATA_ADDR);
 }
 
+uint64_t smn_read64(uint32_t reg)
+{
+	return smn_read32(reg) | (uint64_t)smn_read32(reg + 4) << 32;
+}
+
 void smn_write32(uint32_t reg, uint32_t val)
 {
 	pci_write_config32(SOC_GNB_DEV, SMN_INDEX_ADDR, reg);