sc7180: support bitbang UART w/gpio

Change-Id: I21b149500849eceea663d18a0880c6443ae47d9b
Signed-off-by: T Michael Turney <mturney@codeaurora.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35498
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/qualcomm/sc7180/Kconfig

@@ -11,6 +11,8 @@ config SOC_QUALCOMM_SC7180
 	select HAVE_MONOTONIC_TIMER
 	select ARM64_USE_ARCH_TIMER
 	select SOC_QUALCOMM_COMMON
+	select HAVE_UART_SPECIAL
+	select BOOTBLOCK_CONSOLE
 
 if SOC_QUALCOMM_SC7180
 

src/soc/qualcomm/sc7180/Makefile.inc

@@ -7,11 +7,13 @@ bootblock-y += mmu.c
 bootblock-y += timer.c
 bootblock-y += spi.c
 bootblock-y += gpio.c
+bootblock-$(CONFIG_DRIVERS_UART) += uart_bitbang.c
 
 ################################################################################
 verstage-y += timer.c
 verstage-y += spi.c
 verstage-y += gpio.c
+verstage-$(CONFIG_DRIVERS_UART) += uart_bitbang.c
 
 ################################################################################
 romstage-y += cbmem.c
@@ -22,6 +24,7 @@ romstage-y += ../common/mmu.c
 romstage-y += mmu.c
 romstage-y += spi.c
 romstage-y += gpio.c
+romstage-$(CONFIG_DRIVERS_UART) += uart_bitbang.c
 
 ################################################################################
 ramstage-y += soc.c
@@ -29,6 +32,7 @@ ramstage-y += cbmem.c
 ramstage-y += timer.c
 ramstage-y += spi.c
 ramstage-y += gpio.c
+ramstage-$(CONFIG_DRIVERS_UART) += uart_bitbang.c
 
 ################################################################################
 

src/soc/qualcomm/sc7180/uart_bitbang.c

@@ -0,0 +1,52 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2018 Google LLC
+ * Copyright 2019 The Linux Foundation.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * 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 <console/uart.h>
+#include <gpio.h>
+#include <types.h>
+#include <boot/coreboot_tables.h>
+
+#define UART_TX_PIN GPIO(44)
+
+void uart_fill_lb(void *data)
+{
+
+}
+
+static void set_tx(int line_state)
+{
+	gpio_set(UART_TX_PIN, line_state);
+}
+
+void uart_init(int idx)
+{
+	gpio_output(UART_TX_PIN, 1);
+}
+
+void uart_tx_byte(int idx, unsigned char data)
+{
+	uart_bitbang_tx_byte(data, set_tx);
+}
+
+void uart_tx_flush(int idx)
+{
+	/* unnecessary, PIO Tx means transaction is over when tx_byte returns */
+}
+
+unsigned char uart_rx_byte(int idx)
+{
+	return 0;	/* not implemented */
+}