[v2,6/8] serial: Add Tegra Combined UART driver

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

On 20/06/18 13:20, Mikko Perttunen wrote:
> 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');
> +}

I am curious if we actually need to call uart_set_options() here? Given that
set_termios does nothing, is this actually needed?

> +
> +static struct console tegra_tcu_console = {
> +	.name = "ttyTCU",
> +	.device = uart_console_device,
> +	.flags = CON_PRINTBUFFER | CON_ANYTIME,
> +	.index = -1,
> +	.write = tegra_tcu_console_write,
> +	.setup = tegra_tcu_console_setup,
> +	.data = &tegra_tcu_uart_driver,
> +};
> +
> +static struct uart_driver tegra_tcu_uart_driver = {
> +	.owner = THIS_MODULE,
> +	.driver_name = "tegra-tcu",
> +	.dev_name = "ttyTCU",
> +	.cons = &tegra_tcu_console,
> +	.nr = 1,
> +};
> +
> +static void tegra_tcu_receive(struct mbox_client *client, void *msg_p)
> +{
> +	struct tty_port *port = &tegra_tcu_uart_port.state->port;
> +	uint32_t msg = *(uint32_t *)msg_p;
> +	unsigned int num_bytes;
> +	int i;
> +
> +	num_bytes = TCU_MBOX_NUM_BYTES_V(msg);
> +	for (i = 0; i < num_bytes; i++)
> +		tty_insert_flip_char(port, TCU_MBOX_BYTE_V(msg, i), TTY_NORMAL);
> +
> +	tty_flip_buffer_push(port);
> +}
> +
> +static int tegra_tcu_probe(struct platform_device *pdev)
> +{
> +	struct uart_port *port = &tegra_tcu_uart_port;
> +	struct tegra_tcu *tcu;
> +	int err;
> +
> +	tcu = devm_kzalloc(&pdev->dev, sizeof(*tcu), GFP_KERNEL);
> +	if (!tcu)
> +		return -ENOMEM;
> +
> +	tcu->tx_client.dev = &pdev->dev;
> +	tcu->rx_client.dev = &pdev->dev;
> +	tcu->rx_client.rx_callback = tegra_tcu_receive;
> +
> +	tcu->tx = mbox_request_channel_byname(&tcu->tx_client, "tx");
> +	if (IS_ERR(tcu->tx)) {
> +		err = PTR_ERR(tcu->tx);
> +		dev_err(&pdev->dev, "failed to get tx mailbox: %d\n", err);
> +		return err;
> +	}
> +
> +	tcu->rx = mbox_request_channel_byname(&tcu->rx_client, "rx");
> +	if (IS_ERR(tcu->rx)) {
> +		err = PTR_ERR(tcu->rx);
> +		dev_err(&pdev->dev, "failed to get rx mailbox: %d\n", err);
> +		goto free_tx;
> +	}
> +
> +	err = uart_register_driver(&tegra_tcu_uart_driver);
> +	if (err) {
> +		dev_err(&pdev->dev, "failed to register UART driver: %d\n",
> +			err);
> +		goto free_rx;
> +	}
> +
> +	spin_lock_init(&port->lock);
> +	port->dev = &pdev->dev;
> +	port->type = PORT_TEGRA_TCU;
> +	port->ops = &tegra_tcu_uart_ops;
> +	port->fifosize = 1;
> +	port->iotype = UPIO_MEM;
> +	port->flags = UPF_BOOT_AUTOCONF;
> +	port->private_data = tcu;
> +
> +	err = uart_add_one_port(&tegra_tcu_uart_driver, port);
> +	if (err) {
> +		dev_err(&pdev->dev, "failed to add UART port: %d\n", err);
> +		goto unregister_uart;
> +	}
> +
> +	return 0;
> +
> +unregister_uart:
> +	uart_unregister_driver(&tegra_tcu_uart_driver);
> +free_rx:
> +	mbox_free_channel(tcu->rx);
> +free_tx:
> +	mbox_free_channel(tcu->tx);
> +
> +	return err;
> +}
> +
> +static int tegra_tcu_remove(struct platform_device *pdev)
> +{
> +	uart_remove_one_port(&tegra_tcu_uart_driver, &tegra_tcu_uart_port);
> +	uart_unregister_driver(&tegra_tcu_uart_driver);

mbox_free_channel()?

> +
> +	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 <mperttunen@nvidia.com>");
> +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
> 

Otherwise looks good to me.

Cheers
Jon