[PATCH v3 1/3] ARM: add cpufreq transiton notifier to adjust loops_per_jiffy for smp

Prashant Gaikwad pgaikwad at nvidia.com
Tue Sep 11 07:59:05 EDT 2012

On Monday 10 September 2012 10:47 PM, Stephen Warren wrote:
> On 09/09/2012 07:17 PM, Shawn Guo wrote:
>> On Fri, Sep 07, 2012 at 10:55:00AM -0600, Stephen Warren wrote:
>>> Yes, that does solve the problem (well, with s/late_init/late_initcall/).
>>> As you imply, that change wouldn't help if cpu-tegra.c was built as a
>>> module.
>> I doubt that.  Have you confirmed it with testing?  When you install
>> module cpu-tegra, the pcie initialization has been done, right?
> Never mind, the code can't be built as a module anyway.
> Aside from that, I misinterpreted your test patch, and thought that it
> was moving the Tegra cpufreq driver initialization earlier, but it's
> actually moving it later, and in fact by chance after PCIe
> initialization, which explains why it solves the issue.
> I think the root of the problem is that cpufreq is lowering the CPU
> frequency, yet the patch which converted Tegra to the common clock
> framework removed the code that actually changes the CPU clock rate. So,
> cpufreq thinks the CPU is running at e.g. 216MHz, but it's actually
> still running at 1.0GHz, and hence re-calculating the delay loops breaks
> things, since delays aren't as long as the system thinks they are. The
> variability is due to whether lowering the CPU frequency just happens to
> occur before or after the PCIe controller is initialized.
> Prashant, are you able to fix the clock driver deficiency within the
> next 2-3 days or so (so I can include the fix in the pull requests I
> send for 3.7, which need to be sent before the end of the week)? Or, do
> we need to disable cpufreq for Tegra because of this?

Your fix looks good to me except the concern I have mentioned in reply to that patch.

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