On Mon, 21 Apr 2014, Abhilash Kesavan wrote: > Hi Dave, > > On Thu, Apr 17, 2014 at 3:33 PM, Dave Martin <Dave.Martin@xxxxxxx> wrote: > > On Thu, Apr 17, 2014 at 12:41:31AM +0530, Abhilash Kesavan wrote: > >> The polling loop in the above function was added to ensure that the > >> cluster is switched on before we power on the individual cores in > >> exynos_power_up. This is only required when the first man comes up. > > > > Is this only required on power-up, not power-down? I don't see a call > > to exynos_cluster_power_control(..., 0), but maybe I'm looking in the > > wrong place. > No, you have not missed it. As of now, we are turning on both the L2s > for 8 core bring-up and then not turning it off (if all 4 cores in the > clusters are down). Turning the L2 off (A15 L2 mainly) brings in > significant power savings and I will be looking at adding support for > this next. Good. Please add a comment in the code to that effect in the mean time. > > I wonder whether this is needed, though. It imposes a requirement on > > the OS to waste time polling for the cluster to come online. Can the > > hardware not cope with a CPU poweron request being pending already before > > the cluster is powered on? If that were possible, there would be no need > > for an extra poll. > No, we need to ensure that the cluster L2 is turned On before we can > turn the core on, the hardware does not handle it. > > > > How long do you expect to need to poll for? > In internal testing when we are turning the cluster on from an off > state, I have seen the loop being executed 3-4 times occasionally > during ageing tests. Generally, the status returns as being powered ON > immediately. Looping 3-4 times is pretty reasonable. We certainly can live with that. Nicolas -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
