[PATCH V2] ARM: tegra: retain L2 content over CPU suspend/resume

Joseph Lo josephl at nvidia.com
Tue Nov 13 20:46:52 EST 2012


On Tue, 2012-11-13 at 19:58 +0800, Pavel Machek wrote:
> On Tue 2012-11-13 10:04:48, Joseph Lo wrote:
> > The L2 RAM is in different power domain from the CPU cluster. So the
> > L2 content can be retained over CPU suspend/resume. To do that, we
> > need to disable L2 after the MMU is disabled, and enable L2 before
> > the MMU is enabled. But the L2 controller is in the same power domain
> > with the CPU cluster. We need to restore it's settings and re-enable
> > it after the power be resumed.
> 
> Is it good idea to retain L2 over suspend? I guess this is
> power-vs-speed balance...?
> 

Hi Pavel,

Thanks for your review. Because one of the Tegra's CPU idle state will
shut off the CPU power, it only contain CPU cluster, L1$, GIC and L2
controller. The L2 ram is still powered. The L2 flush is a slow
operation at low frequency. The CPU idle "power-down" state is likely to
happen often at low frequency for low power use case (e.g. low power
audio playback). So yes, it's power-vs-speed balance.

For the system-wide sleep mode (i.e. suspend), the power of L2 RAM would
be shut off at the deepest sleep mode. There would be different
procedure to handle L2.

Thanks,
Joseph





More information about the linux-arm-kernel mailing list