[RFC 06/11] tty: serial: Add Sunplus Plus1 UART earlycon

[Andreas FÃrber]

Prepare an earlycon driver for Sunplus Plus1 SP7021 SoC.

Based on BPI-F2S-bsp tree.

Signed-off-by: Andreas FÃrber <afaerber@xxxxxxx>
---
 drivers/tty/serial/Kconfig        | 19 +++++++++
 drivers/tty/serial/Makefile       |  1 +
 drivers/tty/serial/sunplus-uart.c | 90 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 110 insertions(+)
 create mode 100644 drivers/tty/serial/sunplus-uart.c

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 880b96201530..ac6dce75c2f3 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -1562,6 +1562,25 @@ config SERIAL_MILBEAUT_USIO_CONSOLE
 	  receives all kernel messages and warnings and which allows logins in
 	  single user mode).
 
+config SERIAL_PLUS1
+	bool "Sunplus Plus1 serial port support"
+	depends on ARCH_SUNPLUS || COMPILE_TEST
+	select SERIAL_CORE
+	help
+	  This driver is for Sunplus Plus1 SP7021 SoC's UART.
+	  Say 'Y' here if you wish to use the on-board serial port.
+	  Otherwise, say 'N'.
+
+config SERIAL_PLUS1_CONSOLE
+	bool "Console on Sunplus Plus1 serial port"
+	depends on SERIAL_PLUS1=y
+	select SERIAL_CORE_CONSOLE
+	select SERIAL_EARLYCON
+	default y
+	help
+	  Say 'Y' here if you wish to use Sunplus SP7021 UART
+	  as the system console. Only earlycon is implemented currently.
+
 endmenu
 
 config SERIAL_MCTRL_GPIO
diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
index d056ee6cca33..fed40fb19ed0 100644
--- a/drivers/tty/serial/Makefile
+++ b/drivers/tty/serial/Makefile
@@ -89,6 +89,7 @@ obj-$(CONFIG_SERIAL_OWL)	+= owl-uart.o
 obj-$(CONFIG_SERIAL_RDA)	+= rda-uart.o
 obj-$(CONFIG_SERIAL_MILBEAUT_USIO) += milbeaut_usio.o
 obj-$(CONFIG_SERIAL_SIFIVE)	+= sifive.o
+obj-$(CONFIG_SERIAL_PLUS1)	+= sunplus-uart.o
 
 # GPIOLIB helpers for modem control lines
 obj-$(CONFIG_SERIAL_MCTRL_GPIO)	+= serial_mctrl_gpio.o
diff --git a/drivers/tty/serial/sunplus-uart.c b/drivers/tty/serial/sunplus-uart.c
new file mode 100644
index 000000000000..959dfab5e07b
--- /dev/null
+++ b/drivers/tty/serial/sunplus-uart.c
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2020 Andreas FÃrber
+ */
+
+#include <linux/bitops.h>
+#include <linux/console.h>
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/serial.h>
+#include <linux/serial_core.h>
+
+#define REG_DATA		0x00
+#define REG_LSR			0x04
+
+#define PLUS1_UART_LSR_TX	BIT(0)
+
+static inline void plus1_uart_write(struct uart_port *port, unsigned int off, u32 val)
+{
+	writel_relaxed(val, port->membase + off);
+}
+
+static inline u32 plus1_uart_read(struct uart_port *port, unsigned int off)
+{
+	return readl_relaxed(port->membase + off);
+}
+
+#ifdef CONFIG_SERIAL_PLUS1_CONSOLE
+
+static void plus1_console_putchar(struct uart_port *port, int ch)
+{
+	if (!port->membase)
+		return;
+
+	while (!(plus1_uart_read(port, REG_LSR) & PLUS1_UART_LSR_TX))
+		cpu_relax();
+
+	plus1_uart_write(port, REG_DATA, ch);
+}
+
+static void plus1_uart_port_write(struct uart_port *port, const char *s,
+				  u_int count)
+{
+	unsigned long flags;
+	int locked;
+
+	local_irq_save(flags);
+
+	if (port->sysrq)
+		locked = 0;
+	else if (oops_in_progress)
+		locked = spin_trylock(&port->lock);
+	else {
+		spin_lock(&port->lock);
+		locked = 1;
+	}
+
+	uart_console_write(port, s, count, plus1_console_putchar);
+
+	if (locked)
+		spin_unlock(&port->lock);
+
+	local_irq_restore(flags);
+}
+
+static void plus1_uart_early_console_write(struct console *co,
+					   const char *s,
+					   u_int count)
+{
+	struct earlycon_device *dev = co->data;
+
+	plus1_uart_port_write(&dev->port, s, count);
+}
+
+static int __init
+plus1_uart_early_console_setup(struct earlycon_device *device, const char *opt)
+{
+	if (!device->port.membase)
+		return -ENODEV;
+
+	device->con->write = plus1_uart_early_console_write;
+
+	return 0;
+}
+OF_EARLYCON_DECLARE(sunplus, "sunplus,sp7021-uart",
+		    plus1_uart_early_console_setup);
+
+#endif
-- 
2.16.4