| Message ID | 1459905949-10358-20-git-send-email-boris.ostrovsky@oracle.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
>>> On 06.04.16 at 03:25, <boris.ostrovsky@oracle.com> 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. > --- a/xen/common/libacpi/build.c > +++ b/xen/common/libacpi/build.c > @@ -555,6 +555,8 @@ void acpi_build_tables(struct acpi_config *config, unsigned long physical) > fadt->x_dsdt = config->mem_ops.v2p(dsdt); > fadt->firmware_ctrl = config->mem_ops.v2p(facs); > fadt->x_firmware_ctrl = config->mem_ops.v2p(facs); > + if ( !(config->table_flags & ACPI_BUILD_IOAPIC) ) > + fadt->flags |= (1<<20); /* HW_REDUCED_ACPI */ I think this would better be made a suitable #define in acpi2_0.h. Jan
On 06/06/2016 09:38 AM, Jan Beulich wrote: >>>> On 06.04.16 at 03:25, <boris.ostrovsky@oracle.com> 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) ..." -boris > >> --- a/xen/common/libacpi/build.c >> +++ b/xen/common/libacpi/build.c >> @@ -555,6 +555,8 @@ void acpi_build_tables(struct acpi_config *config, unsigned long physical) >> fadt->x_dsdt = config->mem_ops.v2p(dsdt); >> fadt->firmware_ctrl = config->mem_ops.v2p(facs); >> fadt->x_firmware_ctrl = config->mem_ops.v2p(facs); >> + if ( !(config->table_flags & ACPI_BUILD_IOAPIC) ) >> + fadt->flags |= (1<<20); /* HW_REDUCED_ACPI */ > I think this would better be made a suitable #define in acpi2_0.h. > > Jan >
>>> On 06.06.16 at 19:31, <boris.ostrovsky@oracle.com> wrote: > On 06/06/2016 09:38 AM, Jan Beulich wrote: >>>>> On 06.04.16 at 03:25, <boris.ostrovsky@oracle.com> 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. Jan
On 06/07/2016 02:06 AM, Jan Beulich wrote: >>>> On 06.06.16 at 19:31, <boris.ostrovsky@oracle.com> wrote: >> On 06/06/2016 09:38 AM, Jan Beulich wrote: >>>>>> On 06.04.16 at 03:25, <boris.ostrovsky@oracle.com> 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? -boris
>>> On 07.06.16 at 16:02, <boris.ostrovsky@oracle.com> wrote: > On 06/07/2016 02:06 AM, Jan Beulich wrote: >>>>> On 06.06.16 at 19:31, <boris.ostrovsky@oracle.com> wrote: >>> On 06/06/2016 09:38 AM, Jan Beulich wrote: >>>>>>> On 06.04.16 at 03:25, <boris.ostrovsky@oracle.com> 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
On 06/07/2016 10:12 AM, Jan Beulich wrote: >>>> On 07.06.16 at 16:02, <boris.ostrovsky@oracle.com> wrote: >> On 06/07/2016 02:06 AM, Jan Beulich wrote: >>>>>> On 06.06.16 at 19:31, <boris.ostrovsky@oracle.com> wrote: >>>> On 06/06/2016 09:38 AM, Jan Beulich wrote: >>>>>>>> On 06.04.16 at 03:25, <boris.ostrovsky@oracle.com> 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. Who should those people be? linux-acpi? > 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). FWIW, the Microsoft's reading is https://msdn.microsoft.com/en-us/windows/hardware/drivers/bringup/hardware-requirements-for-soc-based-platforms ACPI fixed hardware features such as the following are not required: Power Management (PM) timer Real Time Clock (RTC) wake alarm System Control Interrupt (SCI) Fixed Hardware register set (PMx_* event/control/status registers) GPE block registers (GPEx_* event/control/status registers) Embedded controller Also, from ACPICA perpective, HW-reduced mode appears to be the only way to prevent initialization of SCI. -boris
>>> On 07.06.16 at 17:17, <boris.ostrovsky@oracle.com> wrote: > On 06/07/2016 10:12 AM, Jan Beulich wrote: >>>>> On 07.06.16 at 16:02, <boris.ostrovsky@oracle.com> wrote: >>> On 06/07/2016 02:06 AM, Jan Beulich wrote: >>>>>>> On 06.06.16 at 19:31, <boris.ostrovsky@oracle.com> wrote: >>>>> On 06/06/2016 09:38 AM, Jan Beulich wrote: >>>>>>>>> On 06.04.16 at 03:25, <boris.ostrovsky@oracle.com> 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. > > Who should those people be? linux-acpi? That may yield valuable, but not dependable input. I'd rather think of folks actually working on / contributing to the spec. I'm sure Intel can name a few of their employees ... >> 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). > > FWIW, the Microsoft's reading is > https://msdn.microsoft.com/en-us/windows/hardware/drivers/bringup/hardware-req > uirements-for-soc-based-platforms > > ACPI fixed hardware features such as the following are not required: > Power Management (PM) timer > Real Time Clock (RTC) wake alarm > System Control Interrupt (SCI) > Fixed Hardware register set (PMx_* event/control/status registers) > GPE block registers (GPEx_* event/control/status registers) > Embedded controller > > Also, from ACPICA perpective, HW-reduced mode appears to be the only way > to prevent initialization of SCI. Well, we could of course start out with HW-reduced mode, but we'd then need to settle on all aspects before any of this becomes fully supported. Jan
On 06/07/2016 11:41 AM, Jan Beulich wrote: >>>> On 07.06.16 at 17:17, <boris.ostrovsky@oracle.com> wrote: >> On 06/07/2016 10:12 AM, Jan Beulich wrote: >>>>>> On 07.06.16 at 16:02, <boris.ostrovsky@oracle.com> wrote: >>>> On 06/07/2016 02:06 AM, Jan Beulich wrote: >>>>>>>> On 06.06.16 at 19:31, <boris.ostrovsky@oracle.com> wrote: >>>>>> On 06/06/2016 09:38 AM, Jan Beulich wrote: >>>>>>>>>> On 06.04.16 at 03:25, <boris.ostrovsky@oracle.com> 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. >> Who should those people be? linux-acpi? > That may yield valuable, but not dependable input. I'd rather think of > folks actually working on / contributing to the spec. I'm sure Intel can > name a few of their employees ... > >>> 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). >> FWIW, the Microsoft's reading is >> https://msdn.microsoft.com/en-us/windows/hardware/drivers/bringup/hardware-req >> uirements-for-soc-based-platforms >> >> ACPI fixed hardware features such as the following are not required: >> Power Management (PM) timer >> Real Time Clock (RTC) wake alarm >> System Control Interrupt (SCI) >> Fixed Hardware register set (PMx_* event/control/status registers) >> GPE block registers (GPEx_* event/control/status registers) >> Embedded controller >> >> Also, from ACPICA perpective, HW-reduced mode appears to be the only way >> to prevent initialization of SCI. > Well, we could of course start out with HW-reduced mode, but we'd > then need to settle on all aspects before any of this becomes fully > supported. So it looks like we can avoid needing this mode in Linux by simply allocating an irq descriptor for the SCI. We shouldn't receive anything on that interrupt in PVH anyway. I don't know whether this will work for other OSs (i.e. FreeBSD). -boris
On Wed, Jun 08, 2016 at 06:04:01PM -0400, Boris Ostrovsky wrote: > On 06/07/2016 11:41 AM, Jan Beulich wrote: > >>>> On 07.06.16 at 17:17, <boris.ostrovsky@oracle.com> wrote: > >> On 06/07/2016 10:12 AM, Jan Beulich wrote: > >>>>>> On 07.06.16 at 16:02, <boris.ostrovsky@oracle.com> wrote: > >>>> On 06/07/2016 02:06 AM, Jan Beulich wrote: > >>>>>>>> On 06.06.16 at 19:31, <boris.ostrovsky@oracle.com> wrote: > >>>>>> On 06/06/2016 09:38 AM, Jan Beulich wrote: > >>>>>>>>>> On 06.04.16 at 03:25, <boris.ostrovsky@oracle.com> 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. > >> Who should those people be? linux-acpi? > > That may yield valuable, but not dependable input. I'd rather think of > > folks actually working on / contributing to the spec. I'm sure Intel can > > name a few of their employees ... > > > >>> 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). > >> FWIW, the Microsoft's reading is > >> https://msdn.microsoft.com/en-us/windows/hardware/drivers/bringup/hardware-req > >> uirements-for-soc-based-platforms > >> > >> ACPI fixed hardware features such as the following are not required: > >> Power Management (PM) timer > >> Real Time Clock (RTC) wake alarm > >> System Control Interrupt (SCI) > >> Fixed Hardware register set (PMx_* event/control/status registers) > >> GPE block registers (GPEx_* event/control/status registers) > >> Embedded controller > >> > >> Also, from ACPICA perpective, HW-reduced mode appears to be the only way > >> to prevent initialization of SCI. > > Well, we could of course start out with HW-reduced mode, but we'd > > then need to settle on all aspects before any of this becomes fully > > supported. > > So it looks like we can avoid needing this mode in Linux by simply > allocating an irq descriptor for the SCI. We shouldn't receive anything > on that interrupt in PVH anyway. > > I don't know whether this will work for other OSs (i.e. FreeBSD). I will have to check this, but AFAICT, setting the Hardware-Reduced ACPI make sense IMHO for DomU, since we are not providing a PM timer, RTC, SCI or any of those PMx and GPEx registers. Not setting it would mean that we would have to provide all those in order to comply with the ACPI specification. Roger.
>>> On 09.06.16 at 10:13, <roger.pau@citrix.com> wrote: > On Wed, Jun 08, 2016 at 06:04:01PM -0400, Boris Ostrovsky wrote: >> On 06/07/2016 11:41 AM, Jan Beulich wrote: >> >>>> On 07.06.16 at 17:17, <boris.ostrovsky@oracle.com> wrote: >> >> On 06/07/2016 10:12 AM, Jan Beulich wrote: >> >>>>>> On 07.06.16 at 16:02, <boris.ostrovsky@oracle.com> wrote: >> >>>> On 06/07/2016 02:06 AM, Jan Beulich wrote: >> >>>>>>>> On 06.06.16 at 19:31, <boris.ostrovsky@oracle.com> wrote: >> >>>>>> On 06/06/2016 09:38 AM, Jan Beulich wrote: >> >>>>>>>>>> On 06.04.16 at 03:25, <boris.ostrovsky@oracle.com> 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. >> >> Who should those people be? linux-acpi? >> > That may yield valuable, but not dependable input. I'd rather think of >> > folks actually working on / contributing to the spec. I'm sure Intel can >> > name a few of their employees ... >> > >> >>> 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). >> >> FWIW, the Microsoft's reading is >> >> > https://msdn.microsoft.com/en-us/windows/hardware/drivers/bringup/hardware-req > >> >> uirements-for-soc-based-platforms >> >> >> >> ACPI fixed hardware features such as the following are not required: >> >> Power Management (PM) timer >> >> Real Time Clock (RTC) wake alarm >> >> System Control Interrupt (SCI) >> >> Fixed Hardware register set (PMx_* event/control/status registers) >> >> GPE block registers (GPEx_* event/control/status registers) >> >> Embedded controller >> >> >> >> Also, from ACPICA perpective, HW-reduced mode appears to be the only way >> >> to prevent initialization of SCI. >> > Well, we could of course start out with HW-reduced mode, but we'd >> > then need to settle on all aspects before any of this becomes fully >> > supported. >> >> So it looks like we can avoid needing this mode in Linux by simply >> allocating an irq descriptor for the SCI. We shouldn't receive anything >> on that interrupt in PVH anyway. >> >> I don't know whether this will work for other OSs (i.e. FreeBSD). > > I will have to check this, but AFAICT, setting the Hardware-Reduced ACPI > make sense IMHO for DomU, since we are not providing a PM timer, RTC, SCI or > any of those PMx and GPEx registers. Not setting it would mean that we would > have to provide all those in order to comply with the ACPI specification. That's true for the current black-or-white model, but won't be true anymore as soon as we allow other than emulate-all and emulate-nothing. Jan
On 06/09/2016 04:41 AM, Jan Beulich wrote: >>>> On 09.06.16 at 10:13, <roger.pau@citrix.com> wrote: >> On Wed, Jun 08, 2016 at 06:04:01PM -0400, Boris Ostrovsky wrote: >>> On 06/07/2016 11:41 AM, Jan Beulich wrote: >>>>>>> On 07.06.16 at 17:17, <boris.ostrovsky@oracle.com> wrote: >>>>> On 06/07/2016 10:12 AM, Jan Beulich wrote: >>>>>>>>> On 07.06.16 at 16:02, <boris.ostrovsky@oracle.com> wrote: >>>>>>> On 06/07/2016 02:06 AM, Jan Beulich wrote: >>>>>>>>>>> On 06.06.16 at 19:31, <boris.ostrovsky@oracle.com> wrote: >>>>>>>>> On 06/06/2016 09:38 AM, Jan Beulich wrote: >>>>>>>>>>>>> On 06.04.16 at 03:25, <boris.ostrovsky@oracle.com> 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. >>>>> Who should those people be? linux-acpi? >>>> That may yield valuable, but not dependable input. I'd rather think of >>>> folks actually working on / contributing to the spec. I'm sure Intel can >>>> name a few of their employees ... >>>> >>>>>> 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). >>>>> FWIW, the Microsoft's reading is >>>>> >> https://msdn.microsoft.com/en-us/windows/hardware/drivers/bringup/hardware-req >> >>>>> uirements-for-soc-based-platforms >>>>> >>>>> ACPI fixed hardware features such as the following are not required: >>>>> Power Management (PM) timer >>>>> Real Time Clock (RTC) wake alarm >>>>> System Control Interrupt (SCI) >>>>> Fixed Hardware register set (PMx_* event/control/status registers) >>>>> GPE block registers (GPEx_* event/control/status registers) >>>>> Embedded controller >>>>> >>>>> Also, from ACPICA perpective, HW-reduced mode appears to be the only way >>>>> to prevent initialization of SCI. >>>> Well, we could of course start out with HW-reduced mode, but we'd >>>> then need to settle on all aspects before any of this becomes fully >>>> supported. >>> So it looks like we can avoid needing this mode in Linux by simply >>> allocating an irq descriptor for the SCI. We shouldn't receive anything >>> on that interrupt in PVH anyway. >>> >>> I don't know whether this will work for other OSs (i.e. FreeBSD). >> I will have to check this, but AFAICT, setting the Hardware-Reduced ACPI >> make sense IMHO for DomU, since we are not providing a PM timer, RTC, SCI or >> any of those PMx and GPEx registers. Not setting it would mean that we would >> have to provide all those in order to comply with the ACPI specification. > That's true for the current black-or-white model, but won't be > true anymore as soon as we allow other than emulate-all and > emulate-nothing. We probably don't want to be too fine-grained about what we emulate. So one option could be that we either emulate all devices that Roger listed above or none. Also, there is a more definitive answer in the spec about what HW-reduced mode means as far as SCI (and other features) is concerned: "5.2.9 Fixed ACPI Description Table (FADT)", Note above table 5-34. -boris
diff --git a/xen/common/libacpi/build.c b/xen/common/libacpi/build.c index e53b4a7..7f2662a 100644 --- a/xen/common/libacpi/build.c +++ b/xen/common/libacpi/build.c @@ -555,6 +555,8 @@ void acpi_build_tables(struct acpi_config *config, unsigned long physical) fadt->x_dsdt = config->mem_ops.v2p(dsdt); fadt->firmware_ctrl = config->mem_ops.v2p(facs); fadt->x_firmware_ctrl = config->mem_ops.v2p(facs); + if ( !(config->table_flags & ACPI_BUILD_IOAPIC) ) + fadt->flags |= (1<<20); /* HW_REDUCED_ACPI */ set_checksum(fadt, offsetof(struct acpi_header, checksum), sizeof(struct acpi_20_fadt));
With this flags set guests will not try to set up SCI. Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com> --- xen/common/libacpi/build.c | 2 ++ 1 file changed, 2 insertions(+)