linux-kernel - Re: [PATCH E 08/14] OMAP clock: move rate recalc, propagation code up to plat-omap/clock.c

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Date:	Tue, 3 Feb 2009 02:45:31 -0700 (MST)
From:	Paul Walmsley <paul@...an.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
cc:	"Woodruff, Richard" <r-woodruff2@...com>,
	"linux-arm-kernel@...ts.arm.linux.org.uk" 
	<linux-arm-kernel@...ts.arm.linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	tuukka.tikkanen@...ia.com, Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH E 08/14] OMAP clock: move rate recalc, propagation code
 up to plat-omap/clock.c

Hi Russell,

On Sat, 31 Jan 2009, Russell King - ARM Linux wrote:

> On Fri, Jan 30, 2009 at 08:23:49AM -0600, Woodruff, Richard wrote:
> > 
> > > There's one bug that your version highlights in mine - the virtual mpu
> > > clock in omap1 touches the DPLL and repropagates that rate.  I've
> > > removed that repropagation, so that needs fixing.
> > >
> > > However, this raises a question: why is the virtual mpu clock touching
> > > some other part of the clock tree.  I wonder whether this should be
> > > handled a different way, though the first thing that needs answering is
> > > why we have this alias for 'arm_ck' ?
> > 
> > At one point in time the virtual clock allowed control for a set of clocks
> > with some dependencies.  The mpu alias provided a convenient control point.
> 
> >From what I can see (checking both mainline and Tony's tree), this mpu
> alias (virtual_ck_mpu) is not used on OMAP1, which seems to suggest
> that this quirk has become redundant.  If it is redundant, it should
> be removed.
> 
> If there is some code somewhere to use it, this quirk should live with
> the user of the quirk until such time that the user becomes ready to be
> merged.

It was probably an OMAP1 implementation of OPPs, similar to virt_prcm_set 
on OMAP2.  Looks like the tree is missing a CPUFreq driver that uses it.  
Cc'ing Tuukka in case he recalls.

One fix that might solve your particular problem would be to remove the 
parent clock pointer from virtual_ck_mpu.  Neither virtual_ck_mpu or 
virt_prcm_set should need it.


- Paul
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