Subject: Re: [PATCH v5 5/5] powerpc/85xx: add support to JOG feature using cpufreq interface

From: Zhao Chenhui <[email-masked]>
Date: Wed, 6 Jun 2012 18:19:03 +0800

On Tue, Jun 05, 2012 at 10:58:41AM -0500, Scott Wood wrote:
> On 06/05/2012 05:59 AM, Zhao Chenhui wrote:
> > On Fri, Jun 01, 2012 at 06:30:55PM -0500, Scott Wood wrote:
> >> On 05/11/2012 06:53 AM, Zhao Chenhui wrote:
> >>> The jog mode frequency transition process on the MPC8536 is similar to
> >>> the deep sleep process. The driver need save the CPU state and restore
> >>> it after CPU warm reset.
> >>>
> >>> Note:
> >>>  * The I/O peripherals such as PCIe and eTSEC may lose packets during
> >>>    the jog mode frequency transition.
> >>
> >> That might be acceptable for eTSEC, but it is not acceptable to lose
> >> anything on PCIe.  Especially not if you're going to make this "default y".
> > 
> > It is a hardware limitation.
> 
> Then make sure jog isn't used if PCIe is used.
> 
> Maybe you could do something with the suspend infrastructure, but this
> is sufficiently heavyweight that transitions should be manually
> requested, not triggered by the automatic cpufreq governor.
> 
> Does this apply to p1022, or just mpc8536?

Both of them.

> 
> > Peripherals in the platform will not be operating
> > during the jog mode frequency transition process.
> 
> What ensures this?
> 
> -Scott

Hardware ensures it without software intervention.

-Chenhui