linux-kernel - Re: [PATCH] serial-core: resume serial hardware with no_console

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Message-ID: <20090925073617.GA5856@n2100.arm.linux.org.uk>
Date:	Fri, 25 Sep 2009 08:36:17 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Stanislav Brabec <utx@...guin.cz>, linux-kernel@...r.kernel.org,
	gregkh@...e.de, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] serial-core: resume serial hardware with
	no_console_suspend

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@...guin.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.
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