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

From: Tony Lindgren <tony@atomide.com>
To: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	"open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
	Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH v1 0/3] console, serial8250: Disable PM and DMA ops
Date: Wed, 23 May 2018 10:58:59 -0700	[thread overview]
Message-ID: <20180523175859.GO98604@atomide.com> (raw)
In-Reply-To: <CAHp75Ve56pyEC41XZ9i9yxBNberQe=ee2miQL0v9T4vRtkWPBQ@mail.gmail.com>

* Andy Shevchenko <andy.shevchenko@gmail.com> [180522 21:42]:
> On Thu, May 17, 2018 at 10:30 PM, Tony Lindgren <tony@atomide.com> wrote:
> > So how about add some "noidle" kernel command line parameter for console
> > that calls
> > pm_runtime_forbid() and then you have the UART permanently
> > on.
> 
> IIUC _forbid() can be overwritten via sysfs.
> And I would prefer to do other way around, something like console.idle
> and put default for OMAP to yes and no for everything else.

OK yeah console.idle sounds good to me. We should default to a
safe option.

> > Hmm I guess you could make also serial8250_rpm_get() do nothing
> > based on that.
> 
> Have you seen entire series which I keep here:
> https://bitbucket.org/andy-shev/linux/branch/topic/uart/rpm?
> Among other things it gets rid of those specific callbacks entirely.

Well I was not Cc:ed on it, I browsed it in some archive and it
seemed unsafe to me. But if you figured out a way to do it conditionally
based on console.idle without causing regressions.

> > I do agree the serial runtime PM has an issue if it depends on
> > pm_runtime_irq_safe() being set.
> 
> It's more than an issue. The  so called "support" of RPM for UART is
> _based on the hack_.
> I would love to NAK that in the first place if I would have known of it in time.

Hmm well it seems that you too have been patching the 8250_rpm
functions for years and then now what after multiple years you
hit this issue? :)

> >> So, I can, of course just remove callbacks from the console ->write().
> >> Though it will prevent to use kernel console anyway.
> >
> > Please et's not start breaking things, we already see a constant
> > flow of regressions on weekly basis.
> 
> Now we are stick with a hack and the case based on that is against
> fixing things.
> This is how it looks from my side.

Sorry yeah I agree there are issues, but let's fix it properly with
no regressions.

Regards,

TOny