linux-kernel - Re: [PATCH resend] serial_core: Fix pm imbalance on unbind

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Message-ID: <CAMuHMdVQBTiZDdY_2Y+uaYUiAA9jVOCOf5okZuKj1QxVSMZVyQ@mail.gmail.com>
Date:	Thu, 27 Mar 2014 09:38:36 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, linux-serial@...r.kernel.org,
	Linux-sh list <linux-sh@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Geert Uytterhoeven <geert+renesas@...ux-m68k.org>
Subject: Re: [PATCH resend] serial_core: Fix pm imbalance on unbind

On Fri, Mar 21, 2014 at 2:06 PM, Peter Hurley <peter@...leysoftware.com> wrote:
>> When a serial port is closed, uart_close() takes care of shutting down the
>> hardware, and powering it down.
>>
>> When a serial port is unbound while in use, uart_close() bypasses all of
>> this, as this is supposed to be done through uart_hangup() (invoked via
>> tty_vhangup() in uart_remove_one_port()).
>>
>> However, uart_hangup() does not set the hardware's power state, leaving it
>> powered up.  This may also lead to unbounded nesting counts in clock and
>> power management, depending on their internal implementation.
>>
>> Make sure to power down the port in uart_hangup(), except when the port is
>> used as a serial console. For serial consoles, this must be postponed
>> until
>> after their deregistration in uart_remove_one_port() (symmetry with
>> registration in uart_configure_port(), invoked from uart_add_one_port()).
>>
>> After this, the module clock used by the sh-sci driver is disabled on
>> unbind while the serial port is in use.
>>
>> Signed-off-by: Geert Uytterhoeven <geert+renesas@...ux-m68k.org>
>> ---
>>   drivers/tty/serial/serial_core.c |    8 ++++++--
>>   1 file changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/tty/serial/serial_core.c
>> b/drivers/tty/serial/serial_core.c
>> index 2cf5649a6dc0..56dda84f82a5 100644
>> --- a/drivers/tty/serial/serial_core.c
>> +++ b/drivers/tty/serial/serial_core.c
>> @@ -1452,6 +1452,8 @@ static void uart_hangup(struct tty_struct *tty)
>>                 clear_bit(ASYNCB_NORMAL_ACTIVE, &port->flags);
>>                 spin_unlock_irqrestore(&port->lock, flags);
>>                 tty_port_tty_set(port, NULL);
>> +               if (!uart_console(state->uart_port))
>> +                       uart_change_pm(state, UART_PM_STATE_OFF);
>
>
> Ok.

Thanks, I'll send an updated patch handling the non-serial console case only.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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