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Subject[PATCH v6 5/5] drivers/tty/serial: add LiteUART driver
From: Filip Kokosinski <fkokosinski@antmicro.com>

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@antmicro.com>
Signed-off-by: Mateusz Holenko <mholenko@antmicro.com>
---

Notes:
Changes in v6:
- LiteUART ports now stored in xArray
- removed PORT_LITEUART
- fixed formatting
- removed some unnecessary defines

No changes in v5.

Changes in v4:
- fixed copyright header
- removed a wrong dependency on UARTLITE from Kconfig
- added a dependency on LITEX_SOC_CONTROLLER to LITEUART in Kconfig

Changes in v3:
- aliases made optional
- used litex_get_reg/litex_set_reg functions instead of macros
- SERIAL_LITEUART_NR_PORTS renamed to SERIAL_LITEUART_MAX_PORTS
- PORT_LITEUART changed from 122 to 123
- added dependency on LITEX_SOC_CONTROLLER
- patch number changed from 4 to 5

No changes in v2.

MAINTAINERS | 1 +
drivers/tty/serial/Kconfig | 31 +++
drivers/tty/serial/Makefile | 1 +
drivers/tty/serial/liteuart.c | 404 ++++++++++++++++++++++++++++++++++
4 files changed, 437 insertions(+)
create mode 100644 drivers/tty/serial/liteuart.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 51d2d6a61fb0..d855fe807833 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9846,6 +9846,7 @@ M: Mateusz Holenko <mholenko@antmicro.com>
S: Maintained
F: Documentation/devicetree/bindings/*/litex,*.yaml
F: drivers/soc/litex/litex_soc_ctrl.c
+F: drivers/tty/serial/liteuart.c
F: include/linux/litex.h

LIVE PATCHING
diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index adf9e80e7dc9..17aaf0afb27a 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -1562,6 +1562,37 @@ 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 || COMPILE_TEST
+ depends on LITEX_SOC_CONTROLLER
+ 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_MAX_PORTS
+ int "Maximum number of LiteUART ports"
+ depends on SERIAL_LITEUART
+ default "1"
+ help
+ Set this to the maximum number of serial ports you want the driver
+ to support.
+
+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 d056ee6cca33..9f8ba419ff3b 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..22b7612c13ca
--- /dev/null
+++ b/drivers/tty/serial/liteuart.c
@@ -0,0 +1,404 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * LiteUART serial controller (LiteX) Driver
+ *
+ * Copyright (C) 2019-2020 Antmicro <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>
+#include <linux/xarray.h>
+
+/*
+ * CSRs definitions (base address offsets + width)
+ *
+ * The definitions below are true for LiteX SoC configured for 8-bit CSR Bus,
+ * 32-bit aligned.
+ *
+ * Supporting other configurations might require new definitions or a more
+ * generic way of indexing the LiteX CSRs.
+ *
+ * For more details on how CSRs are defined and handled in LiteX, see comments
+ * in the LiteX SoC Driver: drivers/soc/litex/litex_soc_ctrl.c
+ */
+#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 DEFINE_XARRAY_FLAGS(liteuart_array, XA_FLAGS_ALLOC);
+
+#ifdef CONFIG_SERIAL_LITEUART_CONSOLE
+static struct console liteuart_console;
+#endif
+
+static struct uart_driver liteuart_driver = {
+ .owner = THIS_MODULE,
+ .driver_name = "liteuart",
+ .dev_name = "ttyLXU",
+ .major = 0,
+ .minor = 0,
+ .nr = CONFIG_SERIAL_LITEUART_MAX_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 long status;
+
+ while ((status = !litex_get_reg(membase + OFF_RXEMPTY, 1)) == 1) {
+ ch = litex_get_reg(membase + OFF_RXTX, 1);
+ port->icount.rx++;
+
+ /* necessary for RXEMPTY to refresh its value */
+ litex_set_reg(membase + OFF_EV_PENDING, 1, EV_TX | EV_RX);
+
+ /* 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_get_reg(port->membase + OFF_TXFULL, 1))
+ cpu_relax();
+
+ litex_set_reg(port->membase + OFF_RXTX, 1, ch);
+}
+
+static unsigned int liteuart_tx_empty(struct uart_port *port)
+{
+ /* not really tx empty, just checking if tx is not full */
+ if (!litex_get_reg(port->membase + OFF_TXFULL, 1))
+ 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_set_reg(port->membase + OFF_RXTX, 1, port->x_char);
+ 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_set_reg(port->membase + OFF_EV_ENABLE, 1, 0);
+
+ /* 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 "liteuart";
+}
+
+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)
+{
+ /*
+ * Driver core for serial ports forces a non-zero value for port type.
+ * Write an arbitrary value here to accommodate the serial core driver,
+ * as ID part of UAPI is redundant.
+ */
+ port->type = 1;
+}
+
+static int liteuart_verify_port(struct uart_port *port,
+ struct serial_struct *ser)
+{
+ if (port->type != PORT_UNKNOWN && ser->type != 1)
+ 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;
+ struct xa_limit limit;
+ int dev_id, ret;
+
+ /* no device tree */
+ if (!np)
+ return -ENODEV;
+
+ if (!litex_check_accessors())
+ return -EPROBE_DEFER;
+
+ /* look for aliases; auto-enumerate for free index if not found */
+ dev_id = of_alias_get_id(np, "serial");
+ if (dev_id < 0)
+ limit = XA_LIMIT(0, CONFIG_SERIAL_LITEUART_MAX_PORTS);
+ else
+ limit = XA_LIMIT(dev_id, dev_id);
+
+ uart = kzalloc(sizeof(struct liteuart_port), GFP_KERNEL);
+ if (!uart)
+ return -ENOMEM;
+
+ ret = xa_alloc(&liteuart_array, &dev_id, uart, limit, GFP_KERNEL);
+ if (ret)
+ return ret;
+
+ port = &uart->port;
+
+ /* get membase */
+ port->membase = devm_platform_get_and_ioremap_resource(pdev, 0, NULL);
+ if (!port->membase)
+ return -ENXIO;
+
+ /* values not from device tree */
+ port->dev = &pdev->dev;
+ port->iotype = UPIO_MEM;
+ port->flags = UPF_BOOT_AUTOCONF;
+ port->ops = &liteuart_ops;
+ port->regshift = 2;
+ port->fifosize = 16;
+ port->iobase = 1;
+ port->type = PORT_UNKNOWN;
+ port->line = dev_id;
+ spin_lock_init(&port->lock);
+
+ return uart_add_one_port(&liteuart_driver, &uart->port);
+}
+
+static int liteuart_remove(struct platform_device *pdev)
+{
+ return 0;
+}
+
+static const struct of_device_id liteuart_of_match[] = {
+ { .compatible = "litex,liteuart" },
+ {}
+};
+MODULE_DEVICE_TABLE(of, liteuart_of_match);
+
+static struct platform_driver liteuart_platform_driver = {
+ .probe = liteuart_probe,
+ .remove = liteuart_remove,
+ .driver = {
+ .name = "liteuart",
+ .of_match_table = liteuart_of_match,
+ },
+};
+
+#ifdef CONFIG_SERIAL_LITEUART_CONSOLE
+
+static void liteuart_console_write(struct console *co, const char *s,
+ unsigned int count)
+{
+ struct liteuart_port *uart;
+ struct uart_port *port;
+ unsigned long flags;
+
+ uart = (struct liteuart_port *)xa_load(&liteuart_array, co->index);
+ port = &uart->port;
+
+ spin_lock_irqsave(&port->lock, flags);
+ uart_console_write(port, s, count, liteuart_putchar);
+ spin_unlock_irqrestore(&port->lock, flags);
+}
+
+static int liteuart_console_setup(struct console *co, char *options)
+{
+ struct liteuart_port *uart;
+ struct uart_port *port;
+ int baud = 115200;
+ int bits = 8;
+ int parity = 'n';
+ int flow = 'n';
+
+ uart = (struct liteuart_port *)xa_load(&liteuart_array, co->index);
+ if (!uart)
+ return -ENODEV;
+
+ port = &uart->port;
+ if (!port->membase)
+ return -ENODEV;
+
+ if (options)
+ uart_parse_options(options, &baud, &parity, &bits, &flow);
+
+ return uart_set_options(port, co, baud, parity, bits, flow);
+}
+
+static struct console liteuart_console = {
+ .name = "liteuart",
+ .write = liteuart_console_write,
+ .device = uart_console_device,
+ .setup = liteuart_console_setup,
+ .flags = CON_PRINTBUFFER,
+ .index = -1,
+ .data = &liteuart_driver,
+};
+
+static int __init liteuart_console_init(void)
+{
+ register_console(&liteuart_console);
+
+ return 0;
+}
+console_initcall(liteuart_console_init);
+#endif /* CONFIG_SERIAL_LITEUART_CONSOLE */
+
+static int __init liteuart_init(void)
+{
+ int res;
+
+ res = uart_register_driver(&liteuart_driver);
+ if (res)
+ return res;
+
+ res = platform_driver_register(&liteuart_platform_driver);
+ if (res) {
+ uart_unregister_driver(&liteuart_driver);
+ return res;
+ }
+
+ return 0;
+}
+
+static void __exit liteuart_exit(void)
+{
+ platform_driver_unregister(&liteuart_platform_driver);
+ uart_unregister_driver(&liteuart_driver);
+}
+
+module_init(liteuart_init);
+module_exit(liteuart_exit);
+
+MODULE_AUTHOR("Antmicro <www.antmicro.com>");
+MODULE_DESCRIPTION("LiteUART serial driver");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform: liteuart");
--
2.20.1
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