soc/amd/common/block/lpc: Add support to not clear port80 enable

SMU locks up sometimes if the port80 enable bit is cleared in the ESPI
Decode register. Add a config to choose between clearing the entire ESPI
Decode Register vs retaining the port80 enable bit.

BUG=None
TEST=Build and boot to OS in Skyrim.

Signed-off-by: Karthikeyan Ramasubramanian <kramasub@google.com>
Change-Id: Ia5ee012ac4858d6dd43827274169edf622a70489
Reviewed-on: https://review.coreboot.org/c/coreboot/+/63118
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>

src/soc/amd/common/block/lpc/Kconfig

@@ -42,3 +42,11 @@ config SOC_AMD_COMMON_BLOCK_USE_ESPI
 	help
 	  Select this option if mainboard uses eSPI instead of LPC (if supported
 	  by platform).
+
+config SOC_AMD_COMMON_BLOCK_ESPI_RETAIN_PORT80_EN
+	bool
+	depends on SOC_AMD_COMMON_BLOCK_USE_ESPI
+	help
+	  SMU will lock up at times if the port80h enable bit is cleared. Select
+	  this option to retain the port80 enable bit while clearing other enable
+	  bits in the ESPI Decode register.

src/soc/amd/common/block/lpc/espi_util.c

@@ -139,6 +139,9 @@ static void espi_clear_decodes(void)
 	unsigned int idx;
 
 	/* First turn off all enable bits, then zero base, range, and size registers */
+	if (CONFIG(SOC_AMD_COMMON_BLOCK_ESPI_RETAIN_PORT80_EN))
+		espi_write16(ESPI_DECODE, (espi_read16(ESPI_DECODE) & ESPI_DECODE_IO_0x80_EN));
+	else
 		espi_write16(ESPI_DECODE, 0);
 
 	for (idx = 0; idx < ESPI_GENERIC_IO_WIN_COUNT; idx++) {