linux-kernel - Re: [PATCH: 2/2] [SERIAL] avoid stalling suspend if serial port won't drain

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Message-ID: <20080114090459.GB4024@elf.ucw.cz>
Date:	Mon, 14 Jan 2008 10:04:59 +0100
From:	Pavel Machek <pavel@....cz>
To:	Russell King <rmk+lkml@....linux.org.uk>
Cc:	Linux Kernel List <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH: 2/2] [SERIAL] avoid stalling suspend if serial port
	won't drain

On Mon 2008-01-14 00:29:12, Russell King wrote:
> On Fri, Jan 11, 2008 at 10:17:21AM +0000, Pavel Machek wrote:
> > On Tue 2008-01-08 11:57:03, Russell King wrote:
> > > +		if (!tries)
> > > +			printk(KERN_ERR "%s%s%s%d: Unable to drain transmitter\n",
> > > +			       port->dev ? port->dev->bus_id : "",
> > > +			       port->dev ? ": " : "",
> > > +			       drv->dev_name, port->line);
> > >  
> > >  		ops->shutdown(port);
> > >  	}
> > > 
> > 
> > Is printk() enough for 'we've just lost your data' condition? Maybe we
> > should abort suspend if we can't drain fifo?
> 
> That would mean that a port set for hardware flow control, with hardware
> implemented flow control, has CTS deasserted, you'll never suspend.

Yep. 

> If you're suspending because your battery is almost dead what would you
> prefer - the system being prevented from suspending and losing complete
> power unexpectedly, resulting in complete data loss, or losing the
> characters in the serial port and suspending?
> 
> Which is the lesser of two evils?

Not sure, but there's third option -- correct but more work. What
about saving/restoring fifo state? That will not stall suspend, nor
will loose data.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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