fixing serial console over suspend [was Re: Bisects that are neither good nor bad]

[Pavel Machek <pavel@ucw.cz>]

On Pá 09-06-06 09:42:34, Russell King wrote:
> On Fri, Jun 09, 2006 at 10:38:33AM +0200, Pavel Machek wrote:
> > > The serial layer does _not_ have access to the "current" termios
> > > settings due to the layering by the tty subsystem.  If the serial
> > > port being used by serial console has been opened once by the user,
> > > but is closed at the moment when a suspend/resume cycle occurs,
> > > the serial layer and lower level drivers do not have access to the
> > > baud rate.
> > 
> > Could serial layer just cache "last baud rate" in some kind of
> > software shadow register? Yes, it is slightly ugly, but should do the trick.
> 
> That's not a new suggestion.  How do you deal with the case where
> you have console on two or more different serial ports?  That's
> the problem with this approach.

Well, each of serial ports has hardware baud_rate register. I'll need
software baud_rate_shadow for every serial port, setting
baud_rate_shadow each time baud_rate is set. During resume, I restore
baud_rate from baud_rate_shadow for each serial port.

What am I missing?

> The only sane solution is for the tty layer to be adjusted to allow
> suspend/resume support for consoles.

Well, solution above is likely to be ugly, but even ugly patch would
help people debug s-to-RAM.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html