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

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Message-Id: <1253872547.13257.18.camel@hammer.suse.cz>
Date:	Fri, 25 Sep 2009 11:55:47 +0200
From:	Stanislav Brabec <utx@...guin.cz>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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

Russell King - ARM Linux wrote:
> 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.

Yes, but no_console_suspend itself is a bit hacky. You need to save
console state but keep it running as long as possible afterwards and
resume it after return from the sleep.

I was not sure, what exactly should be skipped and what must be run, so
I experimented a bit.

Not calling hardware suspend/resume (current implementation) breaks
serial port in hardware that need resume.

Calling of resume without suspend seems to be dangerous. Not calling
suspend at all and standard initialization on resume would probably
reset the port setting and maybe cause memory leak.

> > 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?

The hardware resumes correctly. But no_console_suspend breaks its
resume.

> 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.

Exactly, my ARM hardware is PXA270 on Zaurus SL-C3200.

-- 
Stanislav Brabec
http://www.penguin.cz/~utx

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