linux-kernel - Re: platform/i2c busses: pm runtime and system sleep

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Message-Id: <201102182120.29977.rjw@sisk.pl>
Date:	Fri, 18 Feb 2011 21:20:29 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Rabin Vincent <rabin@....in>
Cc:	stern@...land.harvard.edu, linux-pm@...ts.linux-foundation.org,
	linux-i2c@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel" <linux-arm-kernel@...ts.infradead.org>,
	khilman@...com, magnus.damm@...il.com
Subject: Re: platform/i2c busses: pm runtime and system sleep

On Friday, February 18, 2011, Rabin Vincent wrote:
> On Fri, Feb 18, 2011 at 23:58, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > On Friday, February 18, 2011, Rabin Vincent wrote:
> >> On Thu, Feb 17, 2011 at 20:55, Rabin Vincent <rabin@....in> wrote:
> >> > This will solve the platform vs AMBA bus, but shouldn't we really be
> >> > aiming for consistent behaviour between these and the other busses such
> >> > as I2C and SPI, which are also usually commonly used on the same
> >> > platforms and are using GENERIC_PM_OPS?
> >> >
> >> > Should we be auditing all platform drivers and then switch platform to
> >> > the GENERIC_PM_OPS?
> >> >
> >> > Or should the two points (1) and (2) be not handled in the bus at all
> >> > and be left to individual drivers (in which case we should audit i2c and
> >> > spi and change GENERIC_PM_OPS)?
> >>
> >> How about something like the below?  If we have something like this, we
> >> can just switch platform to GENERIC_PM_OPS and add the
> >> pm_runtime_want_interaction() (or something better named) call to the
> >> i2c and spi drivers using runtime PM.
> >
> > Why don't we make platform_bus_type behave along the lines of generic ops
> > instead?
> 
> At least drivers/spi/omap2_mcspi.c, drivers/video/sh_mobile_lcdcfb.c and
> drivers/watchdog/omap_wdt.c are some pm_runtime-using drivers which seem
> to do different things in their runtime vs normal suspend/resume
> routines, so forcing platform into the active-on-resume behaviour of the
> generic ops may make some use cases impossible.  Conversion of more OMAP
> drivers to runtime pm appears to be ongoing so I'd imagine we'd be
> seeing more of this.  Perhaps Kevin or Magnus will have a comment here.
> The same thing applies to AMBA drivers.

I see.

> Looking at the i2c drivers using runtime pm in comparison, they all seem
> to be using straightforward UNIVERSAL_PM_OPS-style code with the runtime
> and the system sleep doing the same things.  So maybe we do need to
> treat platform/AMBA different from the I2C/SPI group?

We probably do.

Thanks,
Rafael
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