From: Felipe Balbi <balbi@ti.com>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Felipe Balbi <balbi@ti.com>, Greg KH <gregkh@linuxfoundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux ARM Kernel Mailing List
<linux-arm-kernel@lists.infradead.org>,
<linux-pm@vger.kernel.org>,
Linux OMAP Mailing List <linux-omap@vger.kernel.org>,
Russell King <linux@arm.linux.org.uk>,
Tony Lindgren <tony@atomide.com>,
Kevin Hilman <khilman@linaro.org>, Tero Kristo <t-kristo@ti.com>
Subject: Re: [RFC/PATCH] base: platform: add generic clock handling for platform-bus
Date: Fri, 31 Jan 2014 15:44:05 -0600 [thread overview]
Message-ID: <20140131214405.GC2502@saruman.home> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1401311614100.12368-100000@netrider.rowland.org>
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Hi,
On Fri, Jan 31, 2014 at 04:34:27PM -0500, Alan Stern wrote:
> On Fri, 31 Jan 2014, Felipe Balbi wrote:
>
> > Still TODO a commit log. Not for merging!!!!!
> >
> > NYET-Signed-off-by: Felipe Balbi <balbi@ti.com>
> > ---
> >
> > This patch is an idea I've had recently in order to combine several different
> > PM implementations into the platform-bus.
> >
> > This patch is bare minimum for platforms which need to handle functional and
> > interface clocks but the whole thing is made optional.
> >
> > Note that this patch makes sure that by the time a platform_driver's probe is
> > called, we already have clocks enabled and pm_runtime_set_active() has been
> > called, thus making sure that a device driver's pm_runtime_get_sync() will
> > solely increase the pm usage counter.
> >
> > I have *NOT* tested this anywhere *YET*, but I suppose it shouldn't cause any
> > issues since the clock API has ref counting too.
> >
> > Would really like to get some review from several folks involved with ARM SoC
> > PM so that's the reason for the wide audience. If I have missed anybody, please
> > add them to Cc.
> >
> > As mentioned above, this is *NOT* meant for merging, but serves as a starting
> > point for discussing some convergence of several PM domain implementations on
> > different arch/arm/mach-* directories.
>
> You might want to copy the runtime-PM approach used by the PCI
> subsystem. It works like this:
>
> The core invokes a driver's probe routine with runtime PM
> enabled, the device in the ACTIVE state, and the usage counter
> incremented by 1.
>
> If the driver wants to support runtime PM, the probe routine
> can call pm_runtime_put_noidle.
>
> The core does pm_runtime_get_sync before invoking the driver's
> remove routine. At this point a runtime-PM-aware driver whould
> call pm_runtime_get_noresume, to balance the _put during probe.
>
> After invoking the remove routine, the core does a put_noidle
> (to balance the get_sync) and a final put_sync (to balance the
> increment before probe and to leave the device at low power.)
>
> A nice consequence is that everything is transparent for drivers that
> don't support runtime PM. The usage counter remains > 0 the entire
> time the driver is bound.
>
> Conversely, drivers that do support runtime PM merely have to add one
> call during probe and one during remove.
>
> There is one tricky aspect to all this. The driver core sets the
> dev->driver field before calling the subsystem core's probe routine.
> As a result, the subsystem has to be very careful about performing
> runtime PM before invoking the driver's probe routine. Otherwise you
> will end up calling the driver's runtime_resume callback before the
> driver's probe! (And of course, the same problem exists in reverse
> during remove.)
I can, certainly, do that and that would, most likely, simplify a whole
bunch of drivers. But that change, I suppose, would be a whole lot more
invasive. I'll spend some time studying PCI pm_runtime support, thanks
for the tip.
cheers
--
balbi
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next prev parent reply other threads:[~2014-01-31 21:45 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-31 18:12 [RFC/PATCH] base: platform: add generic clock handling for platform-bus Felipe Balbi
2014-01-31 20:04 ` Russell King - ARM Linux
2014-01-31 21:32 ` Felipe Balbi
2014-01-31 21:34 ` Alan Stern
2014-01-31 21:44 ` Felipe Balbi [this message]
2014-03-12 15:37 ` Laurent Pinchart
2014-03-28 13:20 ` Geert Uytterhoeven
2014-03-28 14:41 ` Felipe Balbi
2014-03-28 14:42 ` Felipe Balbi
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