Re: [Qemu-devel] [PATCH RFC] acpi: add reset register to fadt

[Michael S. Tsirkin]

On Tue, Jan 31, 2017 at 04:04:58PM +0000, Phil Dennis-Jordan wrote:
> 
> On Tue, 31 Jan 2017 at 16:41, Igor Mammedov <address@hidden> wrote:
> 
>     On Tue, 31 Jan 2017 16:58:22 +0200
>     "Michael S. Tsirkin" <address@hidden> wrote:
> 
>     > On Tue, Jan 31, 2017 at 03:31:46PM +0100, Phil Dennis-Jordan wrote:
>     > > On 18 January 2017 at 18:19, Igor Mammedov <address@hidden> wrote:
>     > > > On Wed, 18 Jan 2017 18:30:59 +0200
>     > > > "Michael S. Tsirkin" <address@hidden> wrote:
>     > > >
>     > > >> On Wed, Jan 18, 2017 at 12:45:54PM +0100, Phil Dennis-Jordan wrote:
>     > > > [...]
>     > > >
>     > > >> > I suspect more might be involved in enabling ACPI 2.0, and it
>     should probably be an option so as to avoid regressions. I don't know what
>     the best approach would be for this, so comments welcome. Should adding 
> the
>     reset register to the FADT also be configurable?
>     > > >>
>     > > >> I would say an option to make FADT use rev 3 format would be a good
>     > > >> idea.
>     > > >>
>     > > >> I'd make it the default if XP survives.
>     > > > if XP and legacy linux survive,
>     > > > I'd skip adding option as probably there won't be any users,
>     > > > in unlikely case such user surfaces we always can add option later
>     > > > but we can't do it other way around (i.e. take it away).
>     > >
>     > > I have now finally solved the mystery of why my FADT patch has been
>     > > going so disastrously wrong - I've now got working code, but I'd
>     > > appreciate some guidance on the best way to structure a patch to
>     > > minimise further back-and forth.
>     >
>     > + lersek
>     >
>     > > The culprit turned out to be OVMF,
>     > > specifically 2 bugs/shortcomings:
>     > >
>     > > 1. It completely gives up on parsing Qemu's ACPI tables if more than
>     > > one "add pointer" linker command points to the same table. In this
>     > > case, if you add a command for both the DSDT and X_DSDT fields of the
>     > > FADT, it aborts completely and uses fallback tables. (The following
>     > > InstallAcpiTable call fails if called twice with the same table type.)
>     > > https://github.com/tianocore/edk2/blob/master/OvmfPkg/AcpiPlatformDxe/
>     QemuFwCfgAcpi.c#L518
>     > >
>     > > 2. After applying all the linker commands, it goes and rewrites part
>     > > of the FADT anyway. Specifically, it rewrites the DSDT and X_DSDT
>     > > fields - and it always sets one of them to 0. Which one depends on
>     > > whether the DSDT is above the 4G barrier:
>     > > https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Universal/
>     Acpi/AcpiTableDxe/AcpiTableProtocol.c#L650
>     > >
>     > > Both of these are easily fixed, and I will submit a corresponding 
> patch
>     to EDK2.
>     > >
>     > > With that fixed, the rest of the FADT provided by Qemu is accepted by
>     > > OVMF and the operating systems. On the Qemu side, it does mean we'll
>     > > need to still retain the ACPI 1.0 tables for backwards compatibility.
>     > >
>     > > Q1: How should the option be structured and named? Should the FADT
>     > > revision be selectable via a sub-option on -machine? Or as a
>     > > standalone option? Something else?
>     WinXP is main reason why we are using 1.0 revisions,
>     but if bumping revision doesn't affect it or later versions
>     and linux kernel (ancient/contemporary) boots fine,
>     I wouldn't bother with yet another option.
> 
> 
> 
> XP is fine. My concern is that setups with OVMF+Windows (10 confirmed, but
> probably 7/8 too) will suddenly bluescreen on boot because unpatched OVMF
> delivers a non-compliant FADT.

So for that, there might be a work around if you reorder the
tables in the file.


> 
> 
>     > > Q2: To avoid any more confusion, I'd appreciate
>     > > confirmation/clarification on the X_ and non-X FADT fields in the case
>     > > where 32-bit pointers suffice.
>     > >
>     > > Q2a: DSDT/X_DSDT: Both variants appear to be de-facto required.
>     spec doesn't say that X_DSDT is optional and Windows requires it if field
>     is present.
> 
>     > >
>     > > Q2b: FIRMWARE_CTRL/X_FIRMWARE_CTRL: leave X_FIRMWARE_CTRL zero.
>     > >
>     > > Q2c: X_PM1a_EVT_BLK, X_PM1a_CNT_BLK, X_PM_TMR_BLK: These all state
>     > > "This is a required field" for both variants.
>     > >
>     > > Q2d: GPE0_BLK/X_GPE0_BLK: Both variants state "if this register block
>     > > is not supported, this field contains zero." - I understand this to
>     > > mean that when the register block IS supported and 32-bit, both
>     > > variants must be filled.
>     > >
>     > > In other words, only X_FIRMWARE_CTRL stays zero in Qemu's x86 case.
>     > >
>     > >
>     > > I'll come up with a revised patch in the next few days.
>     > >
>     > > Thanks for your help and patience so far, everyone!
> 
>