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Subject: Re: [PATCH-next 3/3] serial/sysrq: Add MAGIC_SYSRQ_SERIAL_SEQUENCE
To:     Joe Perches <joe@perches.com>, linux-kernel@vger.kernel.org
Cc:     Dmitry Safonov <0x7f454c46@gmail.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>,
        Vasiliy Khoruzhick <vasilykh@arista.com>,
        linux-serial@vger.kernel.org
References: <20200109215444.95995-1-dima@arista.com>
 <20200109215444.95995-4-dima@arista.com>
 <5293a7cb1ccb16275ddb36c7f26fb9e83f4fac9b.camel@perches.com>
From:   Dmitry Safonov <dima@arista.com>
Message-ID: <056bff50-f67e-f00f-c98f-ccb427344691@arista.com>
Date:   Fri, 10 Jan 2020 22:10:15 +0000
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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