Re: [PATCH v2 4/4] drivers/tty/serial: add LiteUART driver

From: Rob Herring
Date: Fri Oct 25 2019 - 20:14:04 EST

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On Wed, Oct 23, 2019 at 11:47:23AM +0200, Mateusz Holenko wrote:
> From: Filip Kokosinski <fkokosinski@xxxxxxxxxxxxxxxxxxxxxxxx>
>
> This commit adds driver for the FPGA-based LiteUART serial controller
> from LiteX SoC builder.
>
> The current implementation supports LiteUART configured
> for 32 bit data width and 8 bit CSR bus width.
>
> It does not support IRQ.
>
> Signed-off-by: Filip Kokosinski <fkokosinski@xxxxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Mateusz Holenko <mholenko@xxxxxxxxxxxx>
> ---
> Changes in v2:
> - used register access functions from newly introduced litex.h
> - patch number changed from 3 to 4
>
> MAINTAINERS | 1 +
> drivers/tty/serial/Kconfig | 30 +++
> drivers/tty/serial/Makefile | 1 +
> drivers/tty/serial/liteuart.c | 373 +++++++++++++++++++++++++++++++
> include/uapi/linux/serial_core.h | 3 +
> 5 files changed, 408 insertions(+)
> create mode 100644 drivers/tty/serial/liteuart.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 1dc783c9edb7..c24a37833e78 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -9499,6 +9499,7 @@ M: Mateusz Holenko <mholenko@xxxxxxxxxxxx>
> S: Maintained
> F: include/linux/litex.h
> F: Documentation/devicetree/bindings/*/litex,*.yaml
> +F: drivers/tty/serial/liteuart.c
>
> LIVE PATCHING
> M: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index 4789b5d62f63..b01fe12a1411 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -1571,6 +1571,36 @@ config SERIAL_MILBEAUT_USIO_CONSOLE
> receives all kernel messages and warnings and which allows logins in
> single user mode).
>
> +config SERIAL_LITEUART
> + tristate "LiteUART serial port support"
> + depends on HAS_IOMEM
> + depends on OF
> + select SERIAL_CORE
> + help
> + This driver is for the FPGA-based LiteUART serial controller from LiteX
> + SoC builder.
> +
> + Say 'Y' here if you wish to use the LiteUART serial controller.
> + Otherwise, say 'N'.
> +
> +config SERIAL_LITEUART_NR_PORTS
> + int "Number of LiteUART ports"
> + depends on SERIAL_LITEUART
> + default "1"
> + help
> + Set this to the number of serial ports you want the driver
> + to support.

It's better if the driver supports a dynamic number of ports.

> +
> +config SERIAL_LITEUART_CONSOLE
> + bool "LiteUART serial port console support"
> + depends on SERIAL_LITEUART=y
> + select SERIAL_CORE_CONSOLE
> + help
> + Say 'Y' here if you wish to use the FPGA-based LiteUART serial controller
> + from LiteX SoC builder as the system console (the system console is the
> + device which receives all kernel messages and warnings and which allows
> + logins in single user mode). Otherwise, say 'N'.
> +
> endmenu
>
> config SERIAL_MCTRL_GPIO
> diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
> index 863f47056539..c8d7e2046284 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-$(CONFIG_SERIAL_LITEUART) += liteuart.o
>
> # GPIOLIB helpers for modem control lines
> obj-$(CONFIG_SERIAL_MCTRL_GPIO) += serial_mctrl_gpio.o
> diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
> new file mode 100644
> index 000000000000..e142f78df57a
> --- /dev/null
> +++ b/drivers/tty/serial/liteuart.c
> @@ -0,0 +1,373 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * LiteUART serial controller (LiteX) Driver
> + *
> + * Copyright (C) 2019 Antmicro Ltd <www.antmicro.com>
> + */
> +
> +#include <linux/console.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_address.h>
> +#include <linux/of_platform.h>
> +#include <linux/serial.h>
> +#include <linux/serial_core.h>
> +#include <linux/timer.h>
> +#include <linux/tty_flip.h>
> +#include <linux/litex.h>
> +
> +/* module-related defines */
> +#define DRIVER_NAME "liteuart"
> +#define DRIVER_MAJOR 0
> +#define DRIVER_MINOR 0
> +#define DEV_NAME "ttyLXU"
> +
> +/* base address offsets */
> +#define OFF_RXTX 0x00
> +#define OFF_TXFULL 0x04
> +#define OFF_RXEMPTY 0x08
> +#define OFF_EV_STATUS 0x0c
> +#define OFF_EV_PENDING 0x10
> +#define OFF_EV_ENABLE 0x14
> +
> +/* events */
> +#define EV_TX 0x1
> +#define EV_RX 0x2
> +
> +struct liteuart_port {
> + struct uart_port port;
> + struct timer_list timer;
> +};
> +
> +#define to_liteuart_port(port) container_of(port, struct liteuart_port, port)
> +
> +static struct liteuart_port liteuart_ports[CONFIG_SERIAL_LITEUART_NR_PORTS];
> +
> +#ifdef CONFIG_SERIAL_LITEUART_CONSOLE
> +static struct console liteuart_console;
> +#endif
> +
> +static struct uart_driver liteuart_driver = {
> + .owner = THIS_MODULE,
> + .driver_name = DRIVER_NAME,
> + .dev_name = DEV_NAME,
> + .major = DRIVER_MAJOR,
> + .minor = DRIVER_MINOR,
> + .nr = CONFIG_SERIAL_LITEUART_NR_PORTS,
> +#ifdef CONFIG_SERIAL_LITEUART_CONSOLE
> + .cons = &liteuart_console,
> +#endif
> +};
> +
> +static void liteuart_timer(struct timer_list *t)
> +{
> + struct liteuart_port *uart = from_timer(uart, t, timer);
> + struct uart_port *port = &uart->port;
> + unsigned char __iomem *membase = port->membase;
> + unsigned int flg = TTY_NORMAL;
> + int ch;
> + unsigned int status;
> +
> + while ((status = !LITEX_READ_REG_OFF(membase, OFF_RXEMPTY)) == 1) {
> + ch = LITEX_READ_REG_OFF(membase, OFF_RXTX);
> + port->icount.rx++;
> +
> + /* necessary for RXEMPTY to refresh its value */
> + LITEX_WRITE_REG_OFF(EV_TX | EV_RX, membase, OFF_EV_PENDING);
> +
> + /* no overflow bits in status */
> + if (!(uart_handle_sysrq_char(port, ch)))
> + uart_insert_char(port, status, 0, ch, flg);
> +
> + tty_flip_buffer_push(&port->state->port);
> + }
> +
> + mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
> +}
> +
> +static void liteuart_putchar(struct uart_port *port, int ch)
> +{
> + while (LITEX_READ_REG_OFF(port->membase, OFF_TXFULL))
> + cpu_relax();
> +
> + LITEX_WRITE_REG_OFF(ch, port->membase, OFF_RXTX);
> +}
> +
> +static unsigned int liteuart_tx_empty(struct uart_port *port)
> +{
> + /* not really tx empty, just checking if tx is not full */
> + if (!LITEX_READ_REG_OFF(port->membase, OFF_TXFULL))
> + return TIOCSER_TEMT;
> +
> + return 0;
> +}
> +
> +static void liteuart_set_mctrl(struct uart_port *port, unsigned int mctrl)
> +{
> + /* modem control register is not present in LiteUART */
> +}
> +
> +static unsigned int liteuart_get_mctrl(struct uart_port *port)
> +{
> + return TIOCM_CTS | TIOCM_DSR | TIOCM_CAR;
> +}
> +
> +static void liteuart_stop_tx(struct uart_port *port)
> +{
> +}
> +
> +static void liteuart_start_tx(struct uart_port *port)
> +{
> + struct circ_buf *xmit = &port->state->xmit;
> + unsigned char ch;
> +
> + if (unlikely(port->x_char)) {
> + LITEX_WRITE_REG_OFF(port->x_char, port->membase, OFF_RXTX);
> + port->icount.tx++;
> + port->x_char = 0;
> + } else if (!uart_circ_empty(xmit)) {
> + while (xmit->head != xmit->tail) {
> + ch = xmit->buf[xmit->tail];
> + xmit->tail = (xmit->tail + 1) & (UART_XMIT_SIZE - 1);
> + port->icount.tx++;
> + liteuart_putchar(port, ch);
> + }
> + }
> +
> + if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
> + uart_write_wakeup(port);
> +}
> +
> +static void liteuart_stop_rx(struct uart_port *port)
> +{
> + struct liteuart_port *uart = to_liteuart_port(port);
> +
> + /* just delete timer */
> + del_timer(&uart->timer);
> +}
> +
> +static void liteuart_break_ctl(struct uart_port *port, int break_state)
> +{
> + /* LiteUART doesn't support sending break signal */
> +}
> +
> +static int liteuart_startup(struct uart_port *port)
> +{
> + struct liteuart_port *uart = to_liteuart_port(port);
> +
> + /* disable events */
> + LITEX_WRITE_REG_OFF(0, port->membase, OFF_EV_ENABLE);
> +
> + /* prepare timer for polling */
> + timer_setup(&uart->timer, liteuart_timer, 0);
> + mod_timer(&uart->timer, jiffies + uart_poll_timeout(port));
> +
> + return 0;
> +}
> +
> +static void liteuart_shutdown(struct uart_port *port)
> +{
> +}
> +
> +static void liteuart_set_termios(struct uart_port *port, struct ktermios *new,
> + struct ktermios *old)
> +{
> + unsigned int baud;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&port->lock, flags);
> +
> + /* update baudrate */
> + baud = uart_get_baud_rate(port, new, old, 0, 460800);
> + uart_update_timeout(port, new->c_cflag, baud);
> +
> + spin_unlock_irqrestore(&port->lock, flags);
> +}
> +
> +static const char *liteuart_type(struct uart_port *port)
> +{
> + return (port->type == PORT_LITEUART) ? DRIVER_NAME : NULL;
> +}
> +
> +static void liteuart_release_port(struct uart_port *port)
> +{
> +}
> +
> +static int liteuart_request_port(struct uart_port *port)
> +{
> + return 0;
> +}
> +
> +static void liteuart_config_port(struct uart_port *port, int flags)
> +{
> + if (flags & UART_CONFIG_TYPE)
> + port->type = PORT_LITEUART;
> +}
> +
> +static int liteuart_verify_port(struct uart_port *port,
> + struct serial_struct *ser)
> +{
> + if (port->type != PORT_UNKNOWN && ser->type != PORT_LITEUART)
> + return -EINVAL;
> +
> + return 0;
> +}
> +
> +static const struct uart_ops liteuart_ops = {
> + .tx_empty = liteuart_tx_empty,
> + .set_mctrl = liteuart_set_mctrl,
> + .get_mctrl = liteuart_get_mctrl,
> + .stop_tx = liteuart_stop_tx,
> + .start_tx = liteuart_start_tx,
> + .stop_rx = liteuart_stop_rx,
> + .break_ctl = liteuart_break_ctl,
> + .startup = liteuart_startup,
> + .shutdown = liteuart_shutdown,
> + .set_termios = liteuart_set_termios,
> + .type = liteuart_type,
> + .release_port = liteuart_release_port,
> + .request_port = liteuart_request_port,
> + .config_port = liteuart_config_port,
> + .verify_port = liteuart_verify_port,
> +};
> +
> +static int liteuart_probe(struct platform_device *pdev)
> +{
> + struct device_node *np = pdev->dev.of_node;
> + struct liteuart_port *uart;
> + struct uart_port *port;
> + int dev_id;
> +
> + /* no device tree */
> + if (!np)
> + return -ENODEV;
> +
> + dev_id = of_alias_get_id(np, "serial");
> + if (dev_id < 0 || dev_id >= CONFIG_SERIAL_LITEUART_NR_PORTS)
> + return -EINVAL;

aliases should be optional. There's a helper to get a free index without
an alias you can use.

Next message: Rob Herring: "Re: [PATCH v2 3/4] dt-bindings: serial: document LiteUART bindings"
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