On Wed, Jul 09, 2014 at 08:31:32AM +0200, Thierry Reding wrote: > * PGP Signed by an unknown key > > On Tue, Jul 08, 2014 at 05:11:35PM +0300, Peter De Schrijver wrote: > > > > > > > > Yes, but the problem is that you also need clocks and reset of other modules > > > > in the same domain to safely control the domain's status. Eg: the ISPs, VI and > > > > CSI share a domain. VI and CSI are useable without ISP and the ISP lacks > > > > public documentation. So it's not unlikely a VI and CSI driver will upstreamed > > > > someday which means we would need to control the domain and therefore would > > > > need to tell that driver about the ISPs clocks and resets even though the > > > > driver doesn't know anything about the ISP hw otherwise. > > > > > > Can't we make powergates reference counted so that they don't get > > > disabled as long as there are any users? Looking for example at the > > > > We could, but then why not switch to the powerdomain code and make powering > > off a domain a NOP until we sorted out the context save/restore or fixed > > the framework to allow for suspend without turning off the domains? > > Well, one of the reasons why I'm not sure it's worth the effort at this > point is that we can't get rid of the tegra_powergate_*() API anyway > because of backwards compatibility. So we're going to add code (without > getting rid of old code) merely to support some generic framework. That > doesn't sound very useful to me. > We can also convert the existing users to genpd. Today there are only 2 users (gpu/drm/tegra/gr3d.c and pci/host/pci-tegra.c), so that doesn't seem to be an impossible task. > > > display controller driver, modules don't seem to care overly much about > > > the powergate's state except that it needs to be turned on before they > > > touch some of the registers. > > > > > > From a bit of experimentation it also seems like the sequence encoded > > > within tegra_powergate_sequence_power_up() isn't at all necessary. I > > > couldn't find an authoritative reference for that either, so I'm tempted > > > to conclude that it was simply cargo-culted from the dark-ages. > > > > > > So I'm thinking that if we ever move to use power domains for this, we > > > may be able to just drop any extra handling (well, we'd need to keep it > > > for backwards-compatibility... *sigh*) and let drivers handle the clock > > > and reset resources. > > > > > > On the other hand, given that we already need to keep the existing code > > > for backwards-compatibility, I'm not sure there's a real advantage in > > > turning them into power domains, since we'd be adding extra code without > > > an clear gains (especially since it seems like we'd need even more code > > > to properly handle suspend/resume in drivers that need powergates). > > > > > > > Unless we fix the framework to require context save/restore for suspend. > > There is a good reason to do that. context save/restore requires energy > > as well, so it's not a given that turning off domains in system suspend > > will save power. > > I'm not sure I follow. "require context save/restore for suspend" is > what many drivers currently don't support, hence we can't use the > generic PM domains. Perhaps what you're saying is that the PM domain > core code should be enhanced so that domains can be marked so that they > stay on during a suspend/resume cycle. > Exactly. Cheers, Peter. -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
