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

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Date:   Wed, 18 Jul 2018 23:50:33 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        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

* Andy Shevchenko <andriy.shevchenko@...ux.intel.com> [180718 14:54]:
> On Wed, 2018-05-23 at 11:00 -0700, Tony Lindgren wrote:
> > 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.

I'm fine with that as long as we have a way to detach or disable
kernel console from userspace after booting so the console uart can
idle.

> 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?).

Yes in the long run we should get rid of all pm_runtime_irq_safe()
use. It increases the parent dev PM runtime usage count permanently
blocking the whole domain from idling.

Regards,

Tony