On Mon, Jun 22, 2020 at 07:56:20PM +0530, Sumit Garg wrote:
> From: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
>
> Add request_nmi() callback to install a non-maskable interrupt handler
> corresponding to IRQ retrieved from polling interface. If NMI handler
> installation fails due to missing support from underlying irqchip driver
> then fallback to install it as normal interrupt handler.
>
> Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> Co-developed-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> Signed-off-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
> ---
> drivers/tty/serial/kgdboc.c | 35 +++++++++++++++++++++++++++++++++++
> include/linux/kgdb.h | 7 +++++++
> 2 files changed, 42 insertions(+)
>
> diff --git a/drivers/tty/serial/kgdboc.c b/drivers/tty/serial/kgdboc.c
> index 84ffede..263afae 100644
> --- a/drivers/tty/serial/kgdboc.c
> +++ b/drivers/tty/serial/kgdboc.c
> @@ -19,6 +19,9 @@
> #include <linux/console.h>
> #include <linux/vt_kern.h>
> #include <linux/input.h>
> +#include <linux/interrupt.h>
> +#include <linux/irq.h>
> +#include <linux/irqdesc.h>
> #include <linux/module.h>
> #include <linux/platform_device.h>
> #include <linux/serial_core.h>
> @@ -390,12 +393,44 @@ static void kgdboc_post_exp_handler(void)
> kgdboc_restore_input();
> }
>
> +static int kgdb_tty_irq;
> +
> +static int kgdboc_request_nmi(irq_handler_t fn, void *dev_id)
> +{
> + int irq, res;
> +
> + /* Better to avoid double allocation in the tty driver! */
> + if (kgdb_tty_irq)
> + return 0;
> +
> + if (!kgdb_tty_driver->ops->poll_get_irq)
> + return -ENODEV;
> +
> + irq =
> + kgdb_tty_driver->ops->poll_get_irq(kgdb_tty_driver, kgdb_tty_line);
> + if (irq <= 0)
> + return irq ? irq : -ENODEV;
> +
> + irq_set_status_flags(irq, IRQ_NOAUTOEN);
> + res = request_nmi(irq, fn, IRQF_PERCPU, "kgdboc", dev_id);
Why do we need IRQF_PERCPU here. A UART interrupt is not normally
per-cpu?
> + if (res) {
> + res = request_irq(irq, fn, IRQF_SHARED, "kgdboc", dev_id);
IRQF_SHARED?
Currrently there is nothing that prevents concurrent activation of
ttyNMI0 and the underlying serial driver. Using IRQF_SHARED means it
becomes possible for both drivers to try to service the same interrupt.
That risks some rather "interesting" problems.
Daniel.
> + WARN_ON(res);
> + }
> +
> + enable_irq(irq);
> +
> + kgdb_tty_irq = irq;
> + return 0;
> +}
> +
> static struct kgdb_io kgdboc_io_ops = {
> .name = "kgdboc",
> .read_char = kgdboc_get_char,
> .write_char = kgdboc_put_char,
> .pre_exception = kgdboc_pre_exp_handler,
> .post_exception = kgdboc_post_exp_handler,
> + .request_nmi = kgdboc_request_nmi,
> };
>
> #if IS_BUILTIN(CONFIG_KGDB_SERIAL_CONSOLE)
> diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
> index 529116b..b32b044 100644
> --- a/include/linux/kgdb.h
> +++ b/include/linux/kgdb.h
> @@ -16,6 +16,7 @@
> #include <linux/linkage.h>
> #include <linux/init.h>
> #include <linux/atomic.h>
> +#include <linux/interrupt.h>
> #ifdef CONFIG_HAVE_ARCH_KGDB
> #include <asm/kgdb.h>
> #endif
> @@ -276,6 +277,10 @@ struct kgdb_arch {
> * the I/O driver.
> * @post_exception: Pointer to a function that will do any cleanup work
> * for the I/O driver.
> + * @request_nmi: Pointer to a function that can install an non-maskable
> + * interrupt handler that will be called when a character is pending and that
> + * can be cleared by calling @read_char until it returns NO_POLL_CHAR. If NMI
> + * installation fails then fallback to install normal interrupt handler.
> * @cons: valid if the I/O device is a console; else NULL.
> */
> struct kgdb_io {
> @@ -287,6 +292,8 @@ struct kgdb_io {
> void (*deinit) (void);
> void (*pre_exception) (void);
> void (*post_exception) (void);
> + int (*request_nmi)(irq_handler_t nmi_handler,
> + void *dev_id);
> struct console *cons;
> };
>
> --
> 2.7.4
>
