Re: [PATCH] serial-core: resume serial hardware with no_console_suspend

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Thu, Sep 24, 2009 at 05:05:03PM -0700, Andrew Morton wrote:
> On Tue, 15 Sep 2009 15:38:58 +0200
> Stanislav Brabec <utx@penguin.cz> wrote:
> 
> > Hardware may need re-initialization to get serial port working after
> > resume. It does not happen with no_console_suspend. Attached patch
> > attempts to fix it.
> > 
> > The patch attempts to keep hardware running before suspend and run
> > hardware re-initialization after resume. Maybe simpler approach is
> > possible.
> 
> The patch doesn't apply any more and seems like a rather hacky thing to do.
> 
> It appears that you have specific serial hardware which doesn't resume
> correctly?  If so, that's a bug, so how about we start with a bug
> report/description?

It's something that I did point out when the no_console_suspend patch
appeared, but I was overruled/ignored.

The problem is that on ARM hardware, there is no BIOS to re-initialize
hardware.  The kernel has to do restore the entire system hardware
state upon resume.  Unfortunately, no_console_suspend not only prevents
the console from being suspended but _also_ resumed.

The result of that is the console UART is left in a totally uninitialized
state.