Re: em problem in virtualbox since the weekend

On Friday, July 22, 2011 12:19:24 pm Jung-uk Kim wrote:
> On Friday 22 July 2011 08:05 am, John Baldwin wrote:
> > Err, this is clearly illegal.  Consult Table 6-38 from ACPI Spec
> > 3.0b (page 213, actual page 233 in the PDF).  If the _LEN of an
> > Address Space Descriptor is > 0, then _MIF (Min Fixed) must equal
> > _MAF (Max Fixed).  Having one fixed and not the other is explicitly
> > marked "illegal".
> >
> > Furthermore, the case where _MIF == _MAF == 0 has this description:
> >
> >   Fixed size, variable location resource descriptor for _PRS.
> >   _LEN must be a multiple of (_GRA + 1).
> >   OS can pick the resource range that satisfies following
> > conditions:
> >
> >     * Start address is a multiple of (_GRA + 1) and greater or
> > equal to _MIN. * End address is (start_address + _LEN - 1) and less
> > or equal to _MAX.
> >
> > That explicitly states that this is _only_ for _PRS.  Thus, the
> > only valid combination for _CRS for _MIF and _MAF with a length !=
> > 0 is to have both endpoints fixed.
> >
> > Further, note that for the case were _LEN is zero, all valid cases
> > are described by a block starting thus:
> >
> >   Variable size, variable location resource descriptor for _PRS.
> >
> > Given this, the _only_ valid combination for _CRS is Length != 0,
> > and _MIF == _MAF == 1.  All other resources in _CRS are illegal.
> 
> I was sure that my patch is okay because I found an example in the
> 4.0a page 356 had a _CRS example where _MIF == _MAF == _LEN == 0.
> So, I thought it wasn't strictly for _PRS.  I'll ask Intel guys for
> clarification.

Hmm, that does seem to contradict the earlier section. I wonder if that
example is just broken?  It is supposed to be an example talking about
assigning PCI bus numbers.  Note that both of those examples do use a
length of 0, so perhaps they are expecting the OS to ignore them?

> > BTW, this same table is reproduced verbatim in 4.0a (now table 6-40
> > on page 260).
> 
> Hmm...  Maybe I mis-interpreted the table somehow.  Note the
> original code was _MIF == _MAF == 1, and _LEN > 0 but _LEN !=
> (_MAX - _MIN) + 1:
> 
> --------------
> DwordMemory( // Consumed-and-produced resource
>              // (all of low memory space)
>     ResourceProducer,        // bit 0 of general flags is 0
>     PosDecode,               // positive Decode
>     MinFixed,                // Range is not fixed
>     MaxFixed,                // Range is fixed
>     Cacheable,
>     ReadWrite,
>     0x00000000,              // Granularity
>     0x00000000,              // Min (calculated dynamically)
>     0xffdfffff,              // Max = 4GB - 2MB
>     0x00000000,              // Translation
>     0xdfdfffff,              // Range Length (calculated
>                              // dynamically)
>     ,                        // Optional field left blank
>     ,                        // Optional field left blank
>     MEM3                     // Name declaration for this
>                              //  descriptor
>     )
> --------------             
> Intel ACPI Component Architecture
> ASL Optimizing Compiler version 20110527-64
> Copyright (c) 2000 - 2011 Intel Corporation
> 
> vbox.dsl   1103:                      0xdfdfffff,              // Range Length (calculated
> Error    4118 -                                ^ Length is not equal to fixed Min/Max window
> 
> ASL Input:  vbox.dsl - 1425 lines, 52542 bytes, 338 keywords
> Compilation complete. 1 Errors, 0 Warnings, 0 Remarks, 416 Optimizations
> --------------
> 
> Both _MIN and _LEN are dynamically calculated, so I guess the simplest
> fix should have been:
> 
> --- vbox.dsl.orig       2011-07-22 12:01:33.000000000 -0400
> +++ vbox.dsl    2011-07-22 12:03:41.000000000 -0400
> _at__at_ -1100,7 +1100,7 _at__at_
>  
>                       0xffdfffff,              // Max = 4GB - 2MB
>                       0x00000000,              // Translation
> -                     0xdfdfffff,              // Range Length (calculated
> +                     0xffe00000,              // Range Length (calculated
>                                                // dynamically)
>                       ,                        // Optional field left blank
>                       ,                        // Optional field left blank
> 
> This should have satisfied the table without breaking too much. :-(

Well, perhaps the best fix would be to set the length to 0 instead.  Maybe
the compiler is possibly broken here.  The Fixed vs NotFixed matters in terms
of what is actually presented to the OS once the _CRS method has run, not how
_CRS may choose to populate the buffers.  _CRS may dynamically calculate what
the _MAX and _LEN fields are (this is very common), but the finished buffer
that the OS sees is for a fixed resource range, so it should use Fixed for
both endpoints.

So for example, this is what I see on a test system here for the main PCI
memory window region:

                DWordMemory (ResourceProducer, PosDecode, MinFixed, MaxFixed, Cacheable, ReadWrite,
                    0x00000000,         // Granularity
                    0x00000000,         // Range Minimum
                    0x00000000,         // Range Maximum
                    0x00000000,         // Translation Offset
                    0x00000000,         // Length
                    0x00,, _Y00, AddressRangeMemory, TypeStatic)
                ...
            Method (_CRS, 0, Serialized)
            {
                CreateDWordField (RSRC, \_SB.PCI0._Y00._MIN, BTMN)
                CreateDWordField (RSRC, \_SB.PCI0._Y00._MAX, BTMX)
                CreateDWordField (RSRC, \_SB.PCI0._Y00._LEN, BTLN)
                And (TOLM, 0xF000, Local0)
                ShiftLeft (Local0, 0x10, Local0)
                Store (Local0, BTMN)
                Subtract (0xFEC00000, Local0, BTLN)
                Subtract (Add (BTMN, BTLN), 0x01, BTMX)
                ...

Here the resource when the OS sees it will have _LEN != 0 and _MINF == _MAXF
== 1 even though _MIN and _MAX are computed dynamically in _CRS.

-- 
John Baldwin