Re: [PATCH v2 1/1] tty: serial: owl: Add support for kernel debugger

Greg Kroah-Hartman
2021-01-07T15:20:19Z

On Tue, Jan 05, 2021 at 07:02:02PM +0200, Cristian Ciocaltea wrote:
> Implement 'poll_put_char' and 'poll_get_char' callbacks in struct
> 'owl_uart_ops' that enables OWL UART to be used for kernel debugging
> over serial line.
>
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@gmail.com>
> ---
> Changes in v2:
> - Reverted unnecessary changes per Andreas feedback
> - Optimized implementation for 'owl_uart_poll_get_char()'
> and 'owl_uart_poll_put_char()' callbacks
>
> drivers/tty/serial/owl-uart.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/drivers/tty/serial/owl-uart.c b/drivers/tty/serial/owl-uart.c
> index c149f8c30007..54b24669ebc5 100644
> --- a/drivers/tty/serial/owl-uart.c
> +++ b/drivers/tty/serial/owl-uart.c
> @@ -12,6 +12,7 @@
> #include <linux/console.h>
> #include <linux/delay.h>
> #include <linux/io.h>
> +#include <linux/iopoll.h>
> #include <linux/module.h>
> #include <linux/of.h>
> #include <linux/platform_device.h>
> @@ -461,6 +462,26 @@ static void owl_uart_config_port(struct uart_port *port, int flags)
> }
> }
>
> +#ifdef CONFIG_CONSOLE_POLL
> +
> +static int owl_uart_poll_get_char(struct uart_port *port)
> +{
> + if (owl_uart_read(port, OWL_UART_STAT) & OWL_UART_STAT_RFEM)
> + return NO_POLL_CHAR;
> +
> + return owl_uart_read(port, OWL_UART_RXDAT);
> +}
> +
> +static void owl_uart_poll_put_char(struct uart_port *port, unsigned char ch)
> +{
> + while (owl_uart_read(port, OWL_UART_STAT) & OWL_UART_STAT_TFFU)
> + cpu_relax();

Unbounded loops? What could possibly go wrong?

:(

Please don't do that in the kernel, put a max bound on this.

And are you _SURE_ that cpu_relax() is what you want to call here?

thanks,

greg k-h