linux-kernel - Re: [PATCH-next 3/3] serial/sysrq: Add MAGIC_SYSRQ_SERIAL

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Date:   Fri, 10 Jan 2020 22:10:15 +0000
From:   Dmitry Safonov <dima@...sta.com>
To:     Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Vasiliy Khoruzhick <vasilykh@...sta.com>,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH-next 3/3] serial/sysrq: Add MAGIC_SYSRQ_SERIAL_SEQUENCE

Hi Joe,

On 1/10/20 4:50 PM, Joe Perches wrote:
> 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?

Will do, thanks!

> 
>> +static int uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch)
> 
> This function return might read better as bool not int

Yeah, no hard feelings, will convert.

[..]
>> @@ -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.

I think, 256 chars should be enough to send on serial (c)

I'm not aware of a way to put the max string length in Kconfig, so I did
in the patch:
BUILD_BUG_ON(ARRAY_SIZE(sysrq_toggle_seq) >=
sizeof(port->sysrq_seq)*U8_MAX);

Do you have something more elegant in your mind?

Thanks,
          Dmitry