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

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Message-Id: <201201190108.32794.rjw@sisk.pl>
Date:	Thu, 19 Jan 2012 01:08:32 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Simon Glass <sjg@...omium.org>
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

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.

Thanks,
Rafael
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