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SubjectRe: [PATCH-next 3/3] serial/sysrq: Add MAGIC_SYSRQ_SERIAL_SEQUENCE
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On Thu, 2020-01-09 at 21:54 +0000, Dmitry Safonov wrote:
> Many embedded boards have a disconnected TTL level serial which can
> generate some garbage that can lead to spurious false sysrq detects.

trivia:

> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
[]
> @@ -3081,6 +3081,38 @@ void uart_insert_char(struct uart_port *port, unsigned int status,
[]
> +const char sysrq_toggle_seq[] = CONFIG_MAGIC_SYSRQ_SERIAL_SEQUENCE;

static const?

> +static int uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch)

This function return might read better as bool not int

> +{
> + if (sysrq_toggle_seq[0] == '\0')
> + return 0;
> +
> + BUILD_BUG_ON(ARRAY_SIZE(sysrq_toggle_seq) >= sizeof(port->sysrq_seq)*U8_MAX);
> + if (sysrq_toggle_seq[port->sysrq_seq] != ch) {
> + port->sysrq_seq = 0;
> + return 0;
> + }
> +
> + /* Without the last \0 */
> + if (++port->sysrq_seq < (ARRAY_SIZE(sysrq_toggle_seq) - 1)) {
> + port->sysrq = jiffies + HZ*5;
> + return 1;
> + }
> +
> + schedule_work(&sysrq_enable_work);
> +
> + port->sysrq = 0;
> + return 1;
> +}
[]
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index 255e86a474e9..1f4443db5474 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -243,10 +243,10 @@ struct uart_port {
> unsigned long sysrq; /* sysrq timeout */
> unsigned int sysrq_ch; /* char for sysrq */
> unsigned char has_sysrq;
> + unsigned char sysrq_seq; /* index in sysrq_toggle_seq */

unsigned int?

Or maybe set a maximum length of MAGIC_SYSRQ_SERIAL_SEQUENCE.


>
> unsigned char hub6; /* this should be in the 8250 driver */
> unsigned char suspended;
> - unsigned char unused;
> const char *name; /* port name */
> struct attribute_group *attr_group; /* port specific attributes */
> const struct attribute_group **tty_groups; /* all attributes (serial core use only) */
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 330909c600b1..f6f3e82fee25 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -431,6 +431,14 @@ config MAGIC_SYSRQ_SERIAL
> This option allows you to decide whether you want to enable the
> magic SysRq key.
>
> +config MAGIC_SYSRQ_SERIAL_SEQUENCE
> + string "Char sequence that enables magic SysRq over serial"
> + depends on MAGIC_SYSRQ_SERIAL
> + default ""
> + help
> + Specifies a sequence of characters that can follow BREAK to enable
> + SysRq on a serial console.
> +
> config DEBUG_FS
> bool "Debug Filesystem"
> help

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