The kgdb invokes the poll_put_char and poll_get_char when communicating with the host. This patch implement the serial polling hooks for the meson_uart to be used for KGDB debugging over serial line. Signed-off-by: Julien Masson <jmasson@xxxxxxxxxxxx> --- Changes since v1 [0]: * Use readl_poll_timeout_atomic instead of looping with read + cpu_relax -> read every 5 usecs during 1 msec * add some comments [0]: https://lore.kernel.org/lkml/1549015162-17418-1-git-send-email-jmasson@xxxxxxxxxxxx drivers/tty/serial/meson_uart.c | 65 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 65 insertions(+) diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c index 8a84259..bcff572 100644 --- a/drivers/tty/serial/meson_uart.c +++ b/drivers/tty/serial/meson_uart.c @@ -14,6 +14,7 @@ #include <linux/delay.h> #include <linux/init.h> #include <linux/io.h> +#include <linux/iopoll.h> #include <linux/module.h> #include <linux/kernel.h> #include <linux/of.h> @@ -75,6 +76,8 @@ #define AML_UART_PORT_NUM 6 #define AML_UART_DEV_NAME "ttyAML" +#define AML_UART_POLL_USEC 5 +#define AML_UART_TIMEOUT_USEC 1000 static struct uart_driver meson_uart_driver; @@ -426,6 +429,64 @@ static void meson_uart_config_port(struct uart_port *port, int flags) } } +#ifdef CONFIG_CONSOLE_POLL +/* + * Console polling routines for writing and reading from the uart while + * in an interrupt or debug context (i.e. kgdb). + */ + +static int meson_uart_poll_get_char(struct uart_port *port) +{ + u32 c; + unsigned long flags; + + spin_lock_irqsave(&port->lock, flags); + + if (readl(port->membase + AML_UART_STATUS) & AML_UART_RX_EMPTY) + c = NO_POLL_CHAR; + else + c = readl(port->membase + AML_UART_RFIFO); + + spin_unlock_irqrestore(&port->lock, flags); + + return c; +} + +static void meson_uart_poll_put_char(struct uart_port *port, unsigned char c) +{ + unsigned long flags; + u32 reg; + int ret; + + spin_lock_irqsave(&port->lock, flags); + + /* Wait until FIFO is empty or timeout */ + ret = readl_poll_timeout_atomic(port->membase + AML_UART_STATUS, reg, + reg & AML_UART_TX_EMPTY, + AML_UART_POLL_USEC, + AML_UART_TIMEOUT_USEC); + if (ret == -ETIMEDOUT) { + dev_err(port->dev, "Timeout waiting for UART TX EMPTY\n"); + goto out; + } + + /* Write the character */ + writel(c, port->membase + AML_UART_WFIFO); + + /* Wait until FIFO is empty or timeout */ + ret = readl_poll_timeout_atomic(port->membase + AML_UART_STATUS, reg, + reg & AML_UART_TX_EMPTY, + AML_UART_POLL_USEC, + AML_UART_TIMEOUT_USEC); + if (ret == -ETIMEDOUT) + dev_err(port->dev, "Timeout waiting for UART TX EMPTY\n"); + +out: + spin_unlock_irqrestore(&port->lock, flags); +} + +#endif /* CONFIG_CONSOLE_POLL */ + static const struct uart_ops meson_uart_ops = { .set_mctrl = meson_uart_set_mctrl, .get_mctrl = meson_uart_get_mctrl, @@ -441,6 +502,10 @@ static const struct uart_ops meson_uart_ops = { .request_port = meson_uart_request_port, .release_port = meson_uart_release_port, .verify_port = meson_uart_verify_port, +#ifdef CONFIG_CONSOLE_POLL + .poll_get_char = meson_uart_poll_get_char, + .poll_put_char = meson_uart_poll_put_char, +#endif }; #ifdef CONFIG_SERIAL_MESON_CONSOLE -- 2.7.4
