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:	Fri, 30 Jan 2009 08:23:49 -0600
From:	"Woodruff, Richard" <r-woodruff2@...com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Paul Walmsley <paul@...an.com>
CC:	"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>,
	Tony Lindgren <tony@...mide.com>
Subject: RE: [PATCH E 08/14] OMAP clock: move rate recalc, propagation code
 up to plat-omap/clock.c


> 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.

Tukka did original omap1 in this format. I forget its exact meaning.

The original omap2 code had behavior:
        - mpu-dpll had a clock node which allowed direct mpu speed control
        - mpu-virt-clock allowed switching between sets that have fixed ratio dependency which were pegged to current mpu-dll speed.
                * This way round_rate would allow you to discover all valid OPPs.

The first pass OMAP3 code TI did followed omap2 but it wasn't strongly bound by ratio-sets given the multiple async-dplls. Paul has taken code in a bit different direction.  He can comment on current behavior here.

Regards,
Richard W.

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