On Mon, Jun 22, 2020 at 07:56:19PM +0530, Sumit Garg wrote:
> From: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Sumit, to some extent this mail is me yelling at myself two years ago
although, in my defence, at the time I choose not to post it because I
knew it wasn't right.
I'm a bit concerned to see the TODO: comment critiquing this interface
being removed (from patch 3) without this patch being changed to
address that comment.
> Add new API: poll_get_irq() to the polling interface in order for user
> of polling interface to retrieve allocated IRQ corresponding to
> underlying serial device.
>
> Although, serial interface still works in polling mode but interrupt
> associated with serial device can be leveraged for special purposes like
> debugger(kgdb) entry.
>
> Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> ---
> drivers/tty/serial/serial_core.c | 18 ++++++++++++++++++
> include/linux/serial_core.h | 1 +
> include/linux/tty_driver.h | 1 +
> 3 files changed, 20 insertions(+)
>
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 66a5e2f..1bb033c 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -2470,6 +2470,23 @@ static void uart_poll_put_char(struct tty_driver *driver, int line, char ch)
> port->ops->poll_put_char(port, ch);
> uart_port_deref(port);
> }
> +
> +static int uart_poll_get_irq(struct tty_driver *driver, int line)
> +{
> + struct uart_driver *drv = driver->driver_state;
> + struct uart_state *state = drv->state + line;
> + struct uart_port *port;
> + int ret = -ENODEV;
> +
> + port = uart_port_ref(state);
> + if (port && port->ops->poll_get_irq) {
> + ret = port->ops->poll_get_irq(port);
> + uart_port_deref(port);
> + }
> +
> + return ret;
> +}
> +
> #endif
>
> static const struct tty_operations uart_ops = {
> @@ -2505,6 +2522,7 @@ static const struct tty_operations uart_ops = {
> .poll_init = uart_poll_init,
> .poll_get_char = uart_poll_get_char,
> .poll_put_char = uart_poll_put_char,
> + .poll_get_irq = uart_poll_get_irq,
The TODO comments claimed this API was bogus because it doesn't permit
a free and that can cause interoperation problems with the real serial
driver. I'll cover some of that in a reply to patch 3 but for now.
Anyhow, for this patch, what are the expected semantics for
uart_poll_get_irq().
In particular how do they ensure correct interlocking with the real
serial driver underlying it (if kgdb_nmi is active on a serial port
then the underlying driver better not be active at the same time).
Daniel.
> #endif
> };
>
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index 92f5eba..8b132e6 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -78,6 +78,7 @@ struct uart_ops {
> int (*poll_init)(struct uart_port *);
> void (*poll_put_char)(struct uart_port *, unsigned char);
> int (*poll_get_char)(struct uart_port *);
> + int (*poll_get_irq)(struct uart_port *);
> #endif
> };
>
> diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h
> index 3584462..d6da5c5 100644
> --- a/include/linux/tty_driver.h
> +++ b/include/linux/tty_driver.h
> @@ -295,6 +295,7 @@ struct tty_operations {
> int (*poll_init)(struct tty_driver *driver, int line, char *options);
> int (*poll_get_char)(struct tty_driver *driver, int line);
> void (*poll_put_char)(struct tty_driver *driver, int line, char ch);
> + int (*poll_get_irq)(struct tty_driver *driver, int line);
> #endif
> int (*proc_show)(struct seq_file *, void *);
> } __randomize_layout;
> --
> 2.7.4
>
