linux-kernel - Re: [PATCH 3/3] serial: 8250: Add a wakeup

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Date:	Wed, 18 Jan 2012 16:58:27 -0800
From:	Simon Glass <sjg@...omium.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	paulmck@...ux.vnet.ibm.com, Alan Cox <alan@...rguk.ukuu.org.uk>,
	LKML <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH 3/3] serial: 8250: Add a wakeup_capable module param

Hi Rafael,

On Wed, Jan 18, 2012 at 4:08 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Wednesday, January 18, 2012, Simon Glass wrote:
>> [+cc Rafael J. Wysocki <rjw@...k.pl> who I think wrote the wakeup.c code]
>>
>> Hi Alan, Paul,
>>
>> On Tue, Jan 17, 2012 at 8:17 PM, Paul E. McKenney
>> <paulmck@...ux.vnet.ibm.com> wrote:
>> > On Tue, Jan 17, 2012 at 08:10:36PM +0000, Alan Cox wrote:
>> >> On Tue, 17 Jan 2012 10:56:03 -0800
>> >> Simon Glass <sjg@...omium.org> wrote:
>> >>
>> >> > Since serial_core now does not make serial ports wake-up capable by
>> >> > default, add a parameter to support this feature in the 8250 UART.
>> >> > This is the only UART where I think this feature is useful.
>> >>
>> >> NAK
>> >>
>> >> Things should just work for users. Magic parameters is not an
>> >> improvement. If its a performance problem someone needs to fix the rcu
>> >> sync overhead or stop using rcu on that path.
>>
>> OK fair enough, I agree. Every level I move down the source tree
>> affects more people though.
>>
>> >
>> > I must say that I lack context here, even after looking at the patch,
>> > but the synchronize_rcu_expedited() primitives can be used if the latency
>> > of synchronize_rcu() is too large.
>> >
>>
>> Let me provide a bit of context. The serial_core code seems to be the
>> only place in the kernel that does this:
>>
>>               device_init_wakeup(tty_dev, 1);
>>               device_set_wakeup_enable(tty_dev, 0);
>
> It shouldn't do that.
>
> It should just do device_set_wakeup_capable(tty_dev, true) instead.

Ok, that makes sense - thank you for clearing it up. I will do a new patch.

Regards
Simon

>
> Thanks,
> Rafael
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