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 <jmas...@baylibre.com> --- It has been tested on "Le Potato" board: https://libre.computer/products/boards/aml-s905x-cc/ Kernel command line arguments: kgdboc=ttyAML0,115200 kgdbretry=4 nokaslr kgdbcon Kernel modules: CONFIG_DEBUG_INFO=y CONFIG_DEBUG_KERNEL=y CONFIG_FRAME_POINTER=y CONFIG_KGDB=y CONFIG_KGDB_SERIAL_CONSOLE=y Warning: for single step instruction I had to apply this patch: https://lore.kernel.org/patchwork/patch/562423/ drivers/tty/serial/meson_uart.c | 46 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 46 insertions(+) diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c index 8a84259..49b20da 100644 --- a/drivers/tty/serial/meson_uart.c +++ b/drivers/tty/serial/meson_uart.c @@ -426,6 +426,48 @@ 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; + + spin_lock_irqsave(&port->lock, flags); + + while (!(readl(port->membase + AML_UART_STATUS) & AML_UART_TX_EMPTY)) + cpu_relax(); + + writel(c, port->membase + AML_UART_WFIFO); + + while (!(readl(port->membase + AML_UART_STATUS) & AML_UART_TX_EMPTY)) + cpu_relax(); + + 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 +483,10 @@ 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
