On Wed, Mar 14, 2018 at 3:22 AM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote: > On 02/03/18 02:08, dbasehore . wrote: >> 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. > > The reason we do this is to cope with GIC500 having the collection state > in registers instead of memory. If we didn't have this extraordinary > misfeature, FW could do a full save/restore of the ITS, and we wouldn't > have to do anything (which is what the driver currently expects). > > A middle ground approach is to limit the feature to systems where > GITS_TYPER.HCC is non-zero instead of limiting it to GIC500. Pretty easy > to fix. This should have the same effect, as GIC500 is the only > implementation I'm aware of with HCC!=0. > > Given that we're already at -rc5 and that I'd like to queue things for > 4.17, I've made this change myself and queued patches 1 and 3 here[1]. > > Can you please have a look at let me know if that works for you? > Assuming that your fine with only having the GIC500 implementations that have HCC as non-zero getting ITS registers restored in the kernel. As far as I can tell, this can happen in firmware for all implementations. It's only the code to resend that MAPC on resume that needs to be in the kernel. > Thanks, > > M. > > [1] git://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git > irq/irqchip-next > -- > 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
