On 2014-8-15 18:01, Catalin Marinas wrote: > Hanjun, Hi Catalin, > > On Fri, Aug 15, 2014 at 10:09:42AM +0100, Hanjun Guo wrote: >> On 2014-8-14 18:27, Catalin Marinas wrote: >>> On Thu, Aug 14, 2014 at 04:21:25AM +0100, Hanjun Guo wrote: >>>> On 2014-8-14 7:41, Rafael J. Wysocki wrote: >>>>> On Tuesday, August 12, 2014 07:23:47 PM Catalin Marinas wrote: >>>>>> If we consider ACPI unusable on ARM but we still want to start merging >>>>>> patches, we should rather make the config option depend on BROKEN >>>>>> (though if it is that unusable that no real platform can use it, I would >>>>>> rather not merge it at all at this stage). >>>>> >>>>> I agree here. >>>>> >>>>> I would recommend creating a separate branch for that living outside of the >>>>> mainline kernel and merging it when there are real users. >>>> >>>> Real users will coming soon, we already tested this patch set on real hardware >>>> (ARM64 Juno platform), >>> >>> I don't consider Juno a server platform ;) (but it's good enough for >>> development). >>> >>>> and I think ARM64 server chips and platforms will show up before 3.18 >>>> is released. >>> >>> That's what I've heard/seen. The questions I have are (a) whether >>> current ACPI patchset is enough to successfully run Linux on such >>> _hardware_ platform (maybe not fully optimised, for example just WFI >>> cpuidle) and (b) whether we still want to mandate a DT in the kernel for >>> such platforms. >> >> For (a), this patch set is only for ARM64 core, not including platform >> specific device drivers, it will be covered by the binding of _DSD or >> explicit definition of PNP ID/ACPI ID(s). > > So we go back to the discussions we had few months ago in Macau. I'm not > concerned about the core ARM and architected peripherals covered by ACPI > 5.1 (as long as the current patches get positive technical review). But > I'm concerned about the additional bits needed for a real SoC like _DSD > definitions, how they get reviewed/accepted (or is it just the vendor's > problem?). As the _DSD patch set sent out by Intel folks, _DSD definitions are just DT definitions. To use _DSD or not, I think it depends on OEM use cases, we can bring up Juno without _DSD (Graeme is working on that, still need some time to clean up the code). > > I think SBSA is too vague to guarantee a kernel image running on a > compliant platform without additional (vendor-specific) tweaks. So what > I asked for is (1) a document (guide) to define the strict set of ACPI > features and bindings needed for a real SoC and (2) proof that the > guidelines are enough for real hardware. I think we have (1) under > review with some good feedback so far. As for (2), we can probably only > discuss Juno openly. I think you could share the additional Juno patches > on this list so that reviewers can assess the suitability. If we deem > ACPI not (yet) suitable for Juno, is there other platform we could see > patches for? Ok, we will send out all the patches for Juno in next version for review, as mentioned above, we still need more time to clean up the code. > >>> Given the answer to (a) and what other features are needed, we may or >>> may not mandate (b). We were pretty clear few months ago that (b) is >>> still required but at the time we were only openly talking about ACPI >>> 5.0 which was lacking many features. I think we need to revisit that >>> position based on how usable ACPI 5.1 for ARM (and current kernel >>> implementation) is. Would you mind elaborating what an ACPI-only >>> platform miss? >> >> Do you mean something still missing? We still miss some features for >> ARM in ACPI, but I think they are not critical, here is the list I can >> remember: >> - ITS for GICv3/4; >> - SMMU support; >> - CPU idle control. > > I agree, these are not critical at this stage. But they only refer to > architected peripherals. Is there anything else missing for an SoC? Do > we need to define clocks? No, I prefer not. As we discussed in this thread before, we don't need clock definition if we use SBSA compatible UART on Juno. > >> For ACPI 5.1, it fixes many problems for ARM: >> - weak definition for GIC, so we introduce visualization, v2m and >> part of GICv3/4 (redistributors) support. >> - No support for PSCI. Fix it to support PSCI 0.2+; >> - Not support for Always-on timer and SBSA-L1 watchdog. > > These are all good, that's why we shouldn't even talk about ACPI 5.0 in > the ARM context. > >> - How to describe device properties, so _DSD is introduced for >> device probe. > > For the last bullet, is there any review process (at least like what we > have for DT bindings)? On top of such process, do we have guidelines and > example code on how the Linux support should be implemented. As Olof > mentioned, should we see how the DT and ACPI probing paths work > together? I really think we should be very clear here and not let > vendors invent their own independent methods. As said above, Intel folks provided some good examples for that, and clarified a lot of things: https://lkml.org/lkml/2014/8/17/10 > >>> I would expect a new server platform designed with ACPI in mind to >>> require minimal SoC specific code, so we may only see a few patches >>> under drivers/ for such platforms adding ACPI-specific probing (possibly >>> new drivers as well if it's a new component). >>> >>>> For this patch set, DT is the first class citizen at now: >>>> >>>> a) We can always set CONFIG_ACPI as off in Kconfig, and use DT only; >>> >>> Not just off but, based on maturity, depend on EXPERT. >> >> Ok. And don't set ACPI default off (pass acpi=on to enable it)? > > That's my view, just make it clear ACPI is experimental at the Kconfig > level because longer term we won't mandate SoCs to provide both DT and > ACPI tables. I agree with you that if we set ACPI default off, firmware will always pass acpi=on if they want to use ACPI, so I think it would be better to depend on EXPERT instead. Olof, is it ok to you too? Thanks Hanjun -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
