linux-kernel - Re: [Update][PATCH 7/9] PM / Runtime: Add generic clock manipulation rountines for runtime PM

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Date:	Wed, 20 Apr 2011 00:50:04 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	Magnus Damm <magnus.damm@...il.com>,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	Kevin Hilman <khilman@...com>,
	LKML <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Len Brown <lenb@...nel.org>, linux-sh@...r.kernel.org,
	Alan Stern <stern@...land.harvard.edu>,
	Greg KH <gregkh@...e.de>
Subject: Re: [Update][PATCH 7/9] PM / Runtime: Add generic clock manipulation rountines for runtime PM

On Wednesday, April 20, 2011, Paul Mundt wrote:
> On Wed, Apr 20, 2011 at 12:10:50AM +0200, Rafael J. Wysocki wrote:
> > On Tuesday, April 19, 2011, Paul Mundt wrote:
> > > On Tue, Apr 19, 2011 at 11:42:26PM +0200, Rafael J. Wysocki wrote:
> > > > On Tuesday, April 19, 2011, Magnus Damm wrote:
> > > > > Do you have any plans to add support for multiple clocks per struct
> > > > > device? I had some plans to play around with that myself, but if we're
> > > > > moving the code to a common place then this obviously becomes a bit
> > > > > more complicated.
> > > > > 
> > > > > It's rather common that each hardware block in an SoC is connected to
> > > > > more than a single clock. This needs to be managed by software
> > > > > somehow.
> > > > > 
> > > > > So if the plan is to make to the code generic, how about allowing the
> > > > > architecture to associate clocks with each struct device somehow?
> > > > 
> > > > Hmm.  For now, my patchset generally reorganizes the existing code without
> > > > adding new functionality.  Of course, it is possible to add new functionality
> > > > on top of it, but I'd prefer to focus on the "real" power domains support
> > > > first (which I think should be done in a generic way too).
> > > > 
> > > Multiple clocks is not new functionality, it's the common case for the
> > > bulk of the platforms, and something that is already presently handled.
> > 
> > OK
> > 
> > > > The plan is to share as much code as it makes sense between platforms and
> > > > architectures.
> > > 
> > > An admirable plan, but the framework needs to be able to provide at least
> > > the current required level of functionality in order for it to be
> > > adopted, too.
> > 
> > Sure.
> > 
> > > On Mon, Apr 18, 2011 at 09:57:28PM +0200, Rafael J. Wysocki wrote:
> > > > @@ -24,23 +24,18 @@
> > > >  #ifdef CONFIG_PM_RUNTIME
> > > >  static int omap1_pm_runtime_suspend(struct device *dev)
> > > >  {
> > > > -	struct clk *iclk, *fclk;
> > > > -	int ret = 0;
> > > > +	int ret;
> > > >  
> > > >  	dev_dbg(dev, "%s\n", __func__);
> > > >  
> > > >  	ret = pm_generic_runtime_suspend(dev);
> > > > +	if (ret)
> > > > +		return ret;
> > > >  
> > > > -	fclk = clk_get(dev, "fck");
> > > > -	if (!IS_ERR(fclk)) {
> > > > -		clk_disable(fclk);
> > > > -		clk_put(fclk);
> > > > -	}
> > > > -
> > > > -	iclk = clk_get(dev, "ick");
> > > > -	if (!IS_ERR(iclk)) {
> > > > -		clk_disable(iclk);
> > > > -		clk_put(iclk);
> > > > +	ret = pm_runtime_clock_suspend(dev);
> > > > +	if (ret) {
> > > > +		pm_generic_runtime_resume(dev);
> > > > +		return ret;
> > > >  	}
> > > >  
> > > >  	return 0;
> > > 
> > > The before and after changes here are not functionally equivalent. You've
> > > gone from an explicit multi-clock scheme to a single encapsulated one via
> > > pm_runtime_clock_suspend().
> > 
> > You're refferring to the OMAP changes I suppose?
> 
> Yes, but we have similar use cases on SH, too.
> 
> > > Almost every single SH IP block is likewise abstracted in to a function
> > > and interface clock, and OMAP and others are where we modelled this
> > > abstraction on top of in the first place, so there are certainly users
> > > there too.
> > 
> > In fact, the shmobile runtime PM code in arch/arm/mach-shmobile/pm_runtime.c
> > uses only one clock right now.
> > 
> That's more due to general laziness than design. The code in
> arch/sh/kernel/cpu/shmobile/pm_runtime.c goes through a hwblk abstraction
> that functionally maps out for some CPUs via one API what is the function
> clock on other CPUs. The hwblk API was never carried over to the ARM
> side, and so a simplistic single clock case was implemented instead, and
> the drivers with multiple clocks all performed manual clock gating on
> their multiple clocks outside of the context of runtime PM.
> 
> OMAP1 clearly has a demonstratable case for multiple clocks that are
> runtime PM managed, and this is exactly the sort of use case that SH
> requires, too. If we can migrate off of and kill off some short-lived
> ill-conceived APIs in the process, great. IOW, if you solve the OMAP1
> problem then we can easily fix up ARM SH/R-Mobile and regular SH parts to
> comply uniformly.

OK, I'll extend the generic code to cover the OMAP case.

Thanks,
Rafael
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