[RFC] ARM: Cortex-A9: Enable dynamic clock gating

-----Original Message-----
From: linux-arm-kernel-bounces at lists.infradead.org [mailto:linux-
arm-kernel-bounces at lists.infradead.org] On Behalf Of Catalin Marinas
Sent: Friday, March 11, 2011 10:38 PM
To: Todd Poynor
Cc: linux-arm-kernel at lists.infradead.org
Subject: Re: [RFC] ARM: Cortex-A9: Enable dynamic clock gating

On Wed, 2011-02-23 at 03:55 +0000, Todd Poynor wrote:

quoted

Enable dynamic high level clock gating for Cortex-A9 CPUs, as
described in 2.3.3 "Dynamic high level clock gating" of the
Cortex-A9 TRM.  This may cut the clock of the integer core,
system control block, and Data Engine in certain conditions.

Add ARM errata 720791 to avoid corrupting the Jazelle
instruction stream on earlier Cortex-A9 revisions.

Signed-off-by: Todd Poynor <redacted>
---
Can anyone advise whether this feature should be selectively
enabled (or otherwise modified) due to secured register access,
introduced latencies observed, etc.?

This has been tested on a few Tegra 2 boards without problems
observed thus far, and some preliminary testing indicates it
may result in fairly significant power savings.  Any additional
testing greatly appreciated.

I haven't done any benchmarks on this, so can't comment on this.

My view is that something like the boot monitor/firmware should set
this
up, though that's not always the case. On some OMAP boards Linux
runs in
non-secure mode and it will fault when trying to set this bit.

Or this can be also enabled in the SOC PM initiliasation code
instead of generic code so that the kernel is independent of
boot loaders. Ofcourse downside to this is, every SOC will have
this code duplicated.

Regards,
Santosh