drivers: esp32: Add minimal UART driver based on ROM routines

This is a minimal driver enabling console output during the port
bringup.  While the driver works, only one of the three UART devices
are supported, and there isn't any way to change any parameters or
use interrupts.  This will most likely be superceded by a proper
driver after the port has matured.

Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>

arch/xtensa/soc/esp32/linker.ld

@@ -24,6 +24,9 @@
 
 PROVIDE ( __stack = 0x3ffe3f20 );
 
+PROVIDE ( uart_tx_one_char = 0x40009200 );
+PROVIDE ( uart_rx_one_char = 0x400092d0 );
+
 MEMORY
 {
   iram0_0_seg(RX): org = 0x40080000, len = 0x20000

boards/xtensa/esp32/Kconfig.board

@@ -6,4 +6,3 @@
 config BOARD_ESP32
 	bool "ESP32 Development Board"
 	depends on XTENSA
-

boards/xtensa/esp32/esp32_defconfig

@@ -8,3 +8,10 @@ CONFIG_SOC_ESP32=y
 CONFIG_MAIN_STACK_SIZE=2048
 
 CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC=160000000
+
+CONFIG_CONSOLE=y
+CONFIG_SERIAL_HAS_DRIVER=y
+CONFIG_SERIAL=y
+CONFIG_UART_CONSOLE_ON_DEV_NAME="ROMUART"
+CONFIG_UART_CONSOLE=y
+CONFIG_UART_ESP32=y

drivers/serial/Kconfig

@@ -89,4 +89,6 @@ source "drivers/serial/Kconfig.riscv_qemu"
 
 source "drivers/serial/Kconfig.fe310"
 
+source "drivers/serial/Kconfig.esp32"
+
 endif

drivers/serial/Kconfig.esp32

@@ -0,0 +1,7 @@
+menuconfig UART_ESP32
+	bool "ESP32 UART driver"
+	default n
+	select SERIAL_HAS_DRIVER
+	help
+	Enable the ESP32 UART using ROM routines.
+

drivers/serial/Makefile

@@ -18,3 +18,4 @@ obj-$(CONFIG_UART_CC32XX)	+= uart_cc32xx.o
 obj-$(CONFIG_UART_CMSDK_APB)	+= uart_cmsdk_apb.o
 obj-$(CONFIG_UART_RISCV_QEMU)	+= uart_riscv_qemu.o
 obj-$(CONFIG_UART_FE310)	+= uart_fe310.o
+obj-$(CONFIG_UART_ESP32)	+= uart_esp32.o

drivers/serial/uart_esp32.c

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2017 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <uart.h>
+#include <rom/uart.h>
+#include <rom/ets_sys.h>
+#include <errno.h>
+
+static unsigned char esp32_uart_tx(struct device *dev,
+				   unsigned char c)
+{
+	ARG_UNUSED(dev);
+
+	uart_tx_one_char(c);
+
+	return 0;
+}
+
+static int esp32_uart_rx(struct device *dev, unsigned char *p_char)
+{
+	ARG_UNUSED(dev);
+
+	switch (uart_rx_one_char(p_char)) {
+	case OK:
+		return 0;
+	case PENDING:
+		return -EINPROGRESS;
+	case BUSY:
+		return -EBUSY;
+	case CANCEL:
+		return -ECANCELED;
+	default:
+		return -EIO;
+	}
+}
+
+static int esp32_uart_init(struct device *dev)
+{
+	ARG_UNUSED(dev);
+
+	return 0;
+}
+
+
+static const struct uart_driver_api esp32_uart_api = {
+	.poll_in = &esp32_uart_rx,
+	.poll_out = &esp32_uart_tx,
+	.err_check = NULL,
+#ifdef CONFIG_UART_INTERRUPT_DRIVEN
+
+#error "Interrupt-driven ESP32 UART not implemented yet"
+
+#endif
+};
+
+DEVICE_AND_API_INIT(esp32_uart, "ROMUART",
+		    esp32_uart_init, NULL, NULL,
+		    PRE_KERNEL_1, CONFIG_KERNEL_INIT_PRIORITY_DEVICE,
+		    &esp32_uart_api);