linux-kernel - Re: [PATCH v1 0/3] console, serial8250: Disable PM and DMA ops

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Date:   Wed, 18 Jul 2018 17:50:55 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Tony Lindgren <tony@...mide.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v1 0/3] console, serial8250: Disable PM and DMA ops

On Wed, 2018-05-23 at 11:00 -0700, Tony Lindgren wrote:
> * Andy Shevchenko <andy.shevchenko@...il.com> [180522 21:54]:
> > On Thu, May 17, 2018 at 10:48 PM, Tony Lindgren <tony@...mide.com>
> > wrote:
> > > * Andy Shevchenko <andy.shevchenko@...il.com> [180517 16:38]:
> > > > On Thu, May 17, 2018 at 4:48 PM, Tony Lindgren <tony@...mide.com
> > > > > wrote:
> > > > > * Sebastian Andrzej Siewior <bigeasy@...utronix.de> [180516
> > > > > 10:49]:
> > > > > The idea breaking PM seems silly to me considering that we've
> > > > > had
> > > > > it working for years already.
> > > > 
> > > > Same question  / note. World is much more complex than just
> > > > being OMAP.
> > > 
> > > Sorry but you are making assumptions about hardware being powered
> > > on
> > > all the time.
> > 
> > Nope, other way around. The so called "support" _prevents_ our
> > hardware to go to sleep.
> 
> Hmm sorry now I'm all confused what issues you're having.
> 
> I thought you said earlier the issue was that you wanted to keep
> the console enabled all the time and never idle?

Yes, for kernel console.
To be clear, if user supplies "console=ttySx" it keeps powered on
always. But if there is no such parameter, we are fine with RPM.

Letting kernel console do power management on the systems without
irq_safe hack is dangerous in terms of loosing important data (crash, or
some other stuff which needs atomic context: kgdb?).

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy