On Thu, Mar 1, 2018 at 4:29 AM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote: > Hi Mark, > > On 01/03/18 11:41, Mark Rutland wrote: >> On Wed, Feb 28, 2018 at 09:48:18PM -0800, Derek Basehore wrote: >>> Some platforms power off GIC logic in suspend, so we need to >>> save/restore state. The distributor and redistributor registers need >>> to be handled in platform code due to access permissions on those >>> registers, but the ITS registers can be restored in the kernel. >>> >>> Signed-off-by: Derek Basehore <dbasehore@xxxxxxxxxxxx> >> >> How much state do we have to save/restore? >> >> Given we can apparently read all this state, couldn't we *always* save >> the state, then upon resume detect if the state has been lost, restoring >> it if so? >> >> That way, we don't need a property in FW tables for DT or ACPI. > > That's a good point. I guess that we could just compare the saved > GITS_CTLR register and restore the full state only if the ITS comes back > as disabled. > > I'm just a bit worried that it makes it an implicit convention between > kernel an FW, which could change in funny ways. Importantly, the PSCI > spec says states FW should restore *the whole state*. Obviously, it > cannot to that on HW that doesn't allow you to read out the state, hence > the DT flag that outlines the departure from the expected behaviour. > > I'm happy to go either way, but then I have the feeling that we should > go back to quirking it on the actual implementation (GIC500 in this > case) if we're to from the property. > >> >> [...] >> >>> @@ -3261,6 +3363,9 @@ static int __init its_probe_one(struct resource *res, >>> ctlr |= GITS_CTLR_ImDe; >>> writel_relaxed(ctlr, its->base + GITS_CTLR); >>> >>> + if (fwnode_property_present(handle, "reset-on-suspend")) >>> + its->flags |= ITS_FLAGS_SAVE_SUSPEND_STATE; >> >> Does this allow this property on an ACPI system? >> >> If we need this on ACPI, we need a spec update to handle this properly, >> and shouldn't use device properties like this. > > Well spotted. I guess that dropping the property would fix that > altogether, assuming we feel that the above is safe enough. > > Thoughts? I'm fine changing it to get rid of the devicetree property. What's the reason for quirking the behavior though? It's not that much code + data and nothing else relies on the state of the ITS getting disabled across suspend/resume. Even if something did, we'd have to resolve it with this feature anyways. > > M. > -- > Jazz is not dead. It just smells funny... -- 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
