linux-kernel - Re: [PATCH] tty: serial: 8250_core: Do not call set

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Message-ID: <54369F77.5000906@hurleysoftware.com>
Date:	Thu, 09 Oct 2014 10:45:11 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Sudhir Sreedharan <ssreedharan@...sta.com>,
	gregkh@...uxfoundation.org, khilman@...nel.org
CC:	linux-serial@...r.kernel.org, jslaby@...e.cz,
	linux-kernel@...r.kernel.org, olof@...om.net,
	linux-arm-kernel@...ts.infradead.org, geert@...ux-m68k.org
Subject: Re: [PATCH] tty: serial: 8250_core: Do not call set_sleep for console
 port

Hi Sudhir,

On 10/09/2014 09:45 AM, Sudhir Sreedharan wrote:
> In ST16650V2 based serial uarts, while initalizing the PM state,
> LCR registers are being initialized to 0 in serial8250_set_sleep().
> If console port is already initialized and being used, this will
> throws garbage in the console.
> 
> Signed-off-by: Sudhir Sreedharan <ssreedharan@...sta.com>
> ---
>  drivers/tty/serial/8250/8250_core.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index ca5cfdc..994aa25 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -2618,6 +2618,9 @@ void serial8250_do_pm(struct uart_port *port, unsigned int state,
>  {
>  	struct uart_8250_port *p = up_to_u8250p(port);
>  
> +	if (port->cons && (port->cons->flags & CON_ENABLED) && (state == 0))
> +		return;
> +
>  	serial8250_set_sleep(p, state != 0);
>  }
>  EXPORT_SYMBOL(serial8250_do_pm);

Please just fix serial8250_set_sleep() register programming to save and restore the
LCR.

You could also fix:
1. preserving the other EFR bits
2. acquiring the port lock around the register programming. Not entirely sure it's
absolutely necessary because the serial core serializes most heavy duty register
programming with port mutex, but it's probably wise anyway.

Regards,
Peter Hurley

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