On Fri 01 Feb 2019 at 11:10, Corentin Labbe <clabbe.montjoie@xxxxxxxxx> wrote: > On Fri, Feb 01, 2019 at 10:59:22AM +0100, Julien Masson wrote: >> 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> >> --- >> 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(); > > Hello > > Perhaps you could use read_poll_timeout() ? > This will also permit to handle the timeout case. > > Regards Thanks for the tips Corentin. I tested with a poll of 5 usec and 1 msec of timeout. I had to use readl_poll_timeout_atomic(...) since I'm in atomic context (spinlock). I'll send a v2 of this patch. Regards
