[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH RFC 19/20] acpi: Set HW_REDUCED_ACPI in FADT if IOAPIC is not supported
>>> On 07.06.16 at 16:02, <boris.ostrovsky@xxxxxxxxxx> wrote: > On 06/07/2016 02:06 AM, Jan Beulich wrote: >>>>> On 06.06.16 at 19:31, <boris.ostrovsky@xxxxxxxxxx> wrote: >>> On 06/06/2016 09:38 AM, Jan Beulich wrote: >>>>>>> On 06.04.16 at 03:25, <boris.ostrovsky@xxxxxxxxxx> wrote: >>>>> With this flags set guests will not try to set up SCI. >>>> I've just read through the respective ACPI spec section again, and >>>> I couldn't find a reference to SCI from there ("Hardware-Reduced >>>> ACPI"). Can you clarify this connection please. Also there are other >>>> consequences of setting that flag, so in order to understand the >>>> reasons behind this change in case of future problems I think the >>>> description here will need to be significantly extended, despite the >>>> change being so small. >>> My understanding is that hardware-reduced platforms don't use ACPI >>> Platform Event Model (Sec. 4.1.1) and that model requires SCI (and vice >>> versa --- SCI is present when ACPI Platform Event Model is in use). The >>> (somewhat indirect) evidence of this is in section 4.6 "The ACPI >>> Hardware Model" where is says: "In the ACPI Legacy state, the ACPI event >>> model is disabled (no SCIs are generated) ..." >> In the sum of all the non-explicit wording I can only convince myself >> that SCI is a prereq for the event model. Yet I could see this being >> an if-and-only-if, just that I couldn't find any place saying so. > > Not sure how I should interpret this: do you (reluctantly, possibly) > agree that we can use HW-reduced flag to indicate that SCI is not there? I really think we need to get confirmation on this from ACPI folks. And I think (and I said so before) we need to understand all the other implications from setting that flag (i.e. we _cannot_ use this flag _just_ to indicate there's no SCI). Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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