linux-kernel - Re: [RFC/PATCH 10/13] serial: omap: stick to put

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Message-ID: <20120821105702.GX10347@arwen.pp.htv.fi>
Date:	Tue, 21 Aug 2012 13:57:03 +0300
From:	Felipe Balbi <balbi@...com>
To:	"Shilimkar, Santosh" <santosh.shilimkar@...com>
Cc:	Felipe Balbi <balbi@...com>, alan@...ux.intel.com,
	Tony Lindgren <tony@...mide.com>,
	Kevin Hilman <khilman@...com>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel Mailing List 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-serial@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Shubhrajyoti Datta <shubhrajyoti@...com>
Subject: Re: [RFC/PATCH 10/13] serial: omap: stick to put_autosuspend

On Tue, Aug 21, 2012 at 04:12:11PM +0530, Shilimkar, Santosh wrote:
> On Tue, Aug 21, 2012 at 2:45 PM, Felipe Balbi <balbi@...com> wrote:
> > Everytime we're done using our TTY, we want
> > the pm timer to be reinitilized. By sticking
> > to pm_runtime_pm_autosuspend() we make sure
> > that this will always be the case.
> >
> > Signed-off-by: Felipe Balbi <balbi@...com>
> > ---
> >  drivers/tty/serial/omap-serial.c | 33 ++++++++++++++++++++++-----------
> >  1 file changed, 22 insertions(+), 11 deletions(-)
> >
> > diff --git a/drivers/tty/serial/omap-serial.c b/drivers/tty/serial/omap-serial.c
> > index 6ea24c5..458d77c 100644
> > --- a/drivers/tty/serial/omap-serial.c
> > +++ b/drivers/tty/serial/omap-serial.c
> > @@ -164,7 +164,8 @@ static void serial_omap_enable_ms(struct uart_port *port)
> >         pm_runtime_get_sync(up->dev);
> >         up->ier |= UART_IER_MSI;
> >         serial_out(up, UART_IER, up->ier);
> > -       pm_runtime_put(up->dev);
> > +       pm_runtime_mark_last_busy(up->dev);
> > +       pm_runtime_put_autosuspend(up->dev);
> >  }
> >
> Can you please expand the change-log a bit ?
> Didn't follow the time re-init part completely.

It's really just a micro-optimization. The thing is:

if I call pm_runtime_put(), I will not reinitialize the pm timer to
whatever timeout value I used. This means that pm_runtime_put() could
actually execute right away (if timer was about to expire when I called
pm_runtime_put()). While this wouldn't cause any issues, it's better to
reinitialize the timer and make sure if there's another
read/write/set_termios/whatever coming right after this, UART is still
powered up.

I mean, it's really just trying to avoid context save & restore when
UART is still under heavy usage.

Does it make sense ?

-- 
balbi

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