The Tegra Combined UART (TCU) is a mailbox-based mechanism that allows
multiplexing multiple "virtual UARTs" into a single hardware serial
port. The TCU is the primary serial port on Tegra194 devices.

Add a TCU driver utilizing the mailbox framework, as the used mailboxes
are part of Tegra HSP blocks that are already controlled by the Tegra
HSP mailbox driver.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
---

Notes:
    v2:
    - Removed (void) casts for unused variables.
    - Changed the uart_set_options() call to be on one line, even if its
      over 80 characters.
    - Added defines for magic numbers.
    - Style fixes.
    - Changed Kconfig entry to depend on the Tegra HSP driver instead of
      just the mailbox framework.

 drivers/tty/serial/Kconfig       |   9 ++
 drivers/tty/serial/Makefile      |   1 +
 drivers/tty/serial/tegra-tcu.c   | 289 +++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/serial_core.h |   3 +
 4 files changed, 302 insertions(+)
 create mode 100644 drivers/tty/serial/tegra-tcu.c

diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index df8bd0c7b97d..5fdd336e8937 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig

@@ -322,6 +322,15 @@ config SERIAL_TEGRA
 	  are enabled). This driver uses the APB DMA to achieve higher baudrate
 	  and better performance.
 
+config SERIAL_TEGRA_TCU
+	tristate "NVIDIA Tegra Combined UART"
+	depends on ARCH_TEGRA && TEGRA_HSP_MBOX
+	select SERIAL_CORE
+	help
+	  Support for the mailbox-based TCU (Tegra Combined UART) serial port.
+	  TCU is a virtual serial port that allows multiplexing multiple data
+	  streams into a single hardware serial port.
+
 config SERIAL_MAX3100
 	tristate "MAX3100 support"
 	depends on SPI

diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
index daac675612df..4ad82231ff8a 100644
--- a/drivers/tty/serial/Makefile
+++ b/drivers/tty/serial/Makefile

@@ -76,6 +76,7 @@ obj-$(CONFIG_SERIAL_LANTIQ)	+= lantiq.o
 obj-$(CONFIG_SERIAL_XILINX_PS_UART) += xilinx_uartps.o
 obj-$(CONFIG_SERIAL_SIRFSOC) += sirfsoc_uart.o
 obj-$(CONFIG_SERIAL_TEGRA) += serial-tegra.o
+obj-$(CONFIG_SERIAL_TEGRA_TCU) += tegra-tcu.o
 obj-$(CONFIG_SERIAL_AR933X)   += ar933x_uart.o
 obj-$(CONFIG_SERIAL_EFM32_UART) += efm32-uart.o
 obj-$(CONFIG_SERIAL_ARC)	+= arc_uart.o

diff --git a/drivers/tty/serial/tegra-tcu.c b/drivers/tty/serial/tegra-tcu.c
new file mode 100644
index 000000000000..b54ebe2ad917
--- /dev/null
+++ b/drivers/tty/serial/tegra-tcu.c

@@ -0,0 +1,289 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2018, NVIDIA CORPORATION.  All rights reserved.
+ */
+
+#include <linux/console.h>
+#include <linux/mailbox_client.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/serial.h>
+#include <linux/serial_core.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/tty_flip.h>
+
+#define TCU_MBOX_BYTE(i, x)			((x) << (i*8))
+#define TCU_MBOX_BYTE_V(x, i)			(((x) >> (i*8)) & 0xff)
+#define TCU_MBOX_NUM_BYTES(x)			((x) << 24)
+#define TCU_MBOX_NUM_BYTES_V(x)			(((x) >> 24) & 0x3)
+#define TCU_MBOX_FLUSH				BIT(26)
+
+static struct uart_driver tegra_tcu_uart_driver;
+static struct uart_port tegra_tcu_uart_port;
+
+struct tegra_tcu {
+	struct mbox_client tx_client, rx_client;
+	struct mbox_chan *tx, *rx;
+};
+
+static unsigned int tegra_tcu_uart_tx_empty(struct uart_port *port)
+{
+	return TIOCSER_TEMT;
+}
+
+static void tegra_tcu_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
+{
+}
+
+static unsigned int tegra_tcu_uart_get_mctrl(struct uart_port *port)
+{
+	return 0;
+}
+
+static void tegra_tcu_uart_stop_tx(struct uart_port *port)
+{
+}
+
+static void tegra_tcu_write(const char *s, unsigned int count)
+{
+	struct tegra_tcu *tcu = tegra_tcu_uart_port.private_data;
+	unsigned int written = 0, i = 0;
+	bool insert_nl = false;
+	uint32_t value = 0;
+
+	while (i < count) {
+		if (insert_nl) {
+			value |= TCU_MBOX_BYTE(written++, '\n');
+			insert_nl = false;
+			i++;
+		} else if (s[i] == '\n') {
+			value |= TCU_MBOX_BYTE(written++, '\r');
+			insert_nl = true;
+		} else {
+			value |= TCU_MBOX_BYTE(written++, s[i++]);
+		}
+
+		if (written == 3) {
+			value |= TCU_MBOX_NUM_BYTES(3) | TCU_MBOX_FLUSH;
+			mbox_send_message(tcu->tx, &value);
+			value = 0;
+			written = 0;
+		}
+	}
+
+	if (written) {
+		value |= TCU_MBOX_NUM_BYTES(written) | TCU_MBOX_FLUSH;
+		mbox_send_message(tcu->tx, &value);
+	}
+}
+
+static void tegra_tcu_uart_start_tx(struct uart_port *port)
+{
+	struct circ_buf *xmit = &port->state->xmit;
+	unsigned long count;
+
+	for (;;) {
+		count = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
+		if (!count)
+			break;
+
+		tegra_tcu_write(&xmit->buf[xmit->tail], count);
+		xmit->tail = (xmit->tail + count) & (UART_XMIT_SIZE - 1);
+	}
+
+	uart_write_wakeup(port);
+}
+
+static void tegra_tcu_uart_stop_rx(struct uart_port *port)
+{
+}
+
+static void tegra_tcu_uart_break_ctl(struct uart_port *port, int ctl)
+{
+}
+
+static int tegra_tcu_uart_startup(struct uart_port *port)
+{
+	return 0;
+}
+
+static void tegra_tcu_uart_shutdown(struct uart_port *port)
+{
+}
+
+static void tegra_tcu_uart_set_termios(struct uart_port *port,
+				       struct ktermios *new,
+				       struct ktermios *old)
+{
+}
+
+static const struct uart_ops tegra_tcu_uart_ops = {
+	.tx_empty = tegra_tcu_uart_tx_empty,
+	.set_mctrl = tegra_tcu_uart_set_mctrl,
+	.get_mctrl = tegra_tcu_uart_get_mctrl,
+	.stop_tx = tegra_tcu_uart_stop_tx,
+	.start_tx = tegra_tcu_uart_start_tx,
+	.stop_rx = tegra_tcu_uart_stop_rx,
+	.break_ctl = tegra_tcu_uart_break_ctl,
+	.startup = tegra_tcu_uart_startup,
+	.shutdown = tegra_tcu_uart_shutdown,
+	.set_termios = tegra_tcu_uart_set_termios,
+};
+
+static void tegra_tcu_console_write(struct console *cons, const char *s,
+				    unsigned int count)
+{
+	tegra_tcu_write(s, count);
+}
+
+static int tegra_tcu_console_setup(struct console *cons, char *options)
+{
+	if (!tegra_tcu_uart_port.private_data)
+		return -ENODEV;
+
+	return uart_set_options(&tegra_tcu_uart_port, cons, 115200, 'n', 8, 'n');
+}

+
+	return 0;
+}
+
+static const struct of_device_id tegra_tcu_match[] = {
+	{ .compatible = "nvidia,tegra194-tcu" },
+	{ }
+};
+
+static struct platform_driver tegra_tcu_driver = {
+	.driver = {
+		.name = "tegra-tcu",
+		.of_match_table = tegra_tcu_match,
+	},
+	.probe = tegra_tcu_probe,
+	.remove = tegra_tcu_remove,
+};
+
+static int __init tegra_tcu_init(void)
+{
+	int err;
+
+	err = platform_driver_register(&tegra_tcu_driver);
+	if (err)
+		return err;
+
+	register_console(&tegra_tcu_console);
+
+	return 0;
+}
+module_init(tegra_tcu_init);
+
+static void __exit tegra_tcu_exit(void)
+{
+	unregister_console(&tegra_tcu_console);
+	platform_driver_unregister(&tegra_tcu_driver);
+}
+module_exit(tegra_tcu_exit);
+
+MODULE_AUTHOR("Mikko Perttunen [off-list ref]");
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("NVIDIA Tegra Combined UART driver");

diff --git a/include/uapi/linux/serial_core.h b/include/uapi/linux/serial_core.h
index dce5f9dae121..69883c32cb98 100644
--- a/include/uapi/linux/serial_core.h
+++ b/include/uapi/linux/serial_core.h

@@ -79,6 +79,9 @@
 /* Nuvoton UART */
 #define PORT_NPCM	40
 
+/* NVIDIA Tegra Combined UART */
+#define PORT_TEGRA_TCU	41
+
 /* Intel EG20 */
 #define PORT_PCH_8LINE	44
 #define PORT_PCH_2LINE	45