Re: [PATCH v3 3/8] acpi/gpex: Inform os to keep firmware resource map

[Michael S. Tsirkin]

On Tue, Dec 29, 2020 at 02:41:42PM +0100, Igor Mammedov wrote:
> On Wed, 23 Dec 2020 17:08:31 +0800
> Jiahui Cen <cenjiahui@huawei.com> wrote:
> 
> > There may be some differences in pci resource assignment between guest os
> > and firmware.
> > 
> > Eg. A Bridge with Bus [d2]
> >     -+-[0000:d2]---01.0-[d3]----01.0
> > 
> >     where [d2:01.00] is a pcie-pci-bridge with BAR0 (mem, 64-bit, non-pref) 
> > [size=256]
> >           [d3:01.00] is a PCI Device with BAR0 (mem, 64-bit, pref) 
> > [size=128K]
> >                                           BAR4 (mem, 64-bit, pref) 
> > [size=64M]
> > 
> >     In EDK2, the Resource Map would be:
> >         PciBus: Resource Map for Bridge [D2|01|00]
> >         Type = PMem64; Base = 0x8004000000;     Length = 0x4100000;     
> > Alignment = 0x3FFFFFF
> >            Base = 0x8004000000; Length = 0x4000000;     Alignment = 
> > 0x3FFFFFF;  Owner = PCI [D3|01|00:20]
> >            Base = 0x8008000000; Length = 0x20000;       Alignment = 
> > 0x1FFFF;    Owner = PCI [D3|01|00:10]
> >         Type =  Mem64; Base = 0x8008100000;     Length = 0x100; Alignment = 
> > 0xFFF
> >     It would use 0x4100000 to calculate the root bus's PMem64 resource 
> > window.
> > 
> >     While in Linux, kernel will use 0x1FFFFFF as the alignment to calculate
> >     the PMem64 size, which would be 0x6000000. So kernel would try to
> >     allocate 0x6000000 from the PMem64 resource window, but since the window
> >     size is 0x4100000 as assigned by EDK2, the allocation would fail.
> > 
> > The diffences could result in resource assignment failure.
> > 
> > Using _DSM #5 method to inform guest os not to ignore the PCI configuration
> > that firmware has done at boot time could handle the differences.
> 
> I'm not sure about this one, 
> OS should able to reconfigure PCI resources according to what and where is 
> plugged
> (and it even more true is hotplug is taken into account)

spec says this:

0: No (The operating system must not ignore the PCI configuration that firmware 
has done
at boot time. However, the operating system is free to configure the devices in 
this hierarchy
that have not been configured by the firmware. There may be a reduced level of 
hot plug
capability support in this hierarchy due to resource constraints. This 
situation is the same as
the legacy situation where this _DSM is not provided.)
1: Yes (The operating system may ignore the PCI configuration that the firmware 
has done
at boot time, and reconfigure/rebalance the resources in the hierarchy.)

and

IMPLEMENTATION NOTE
This _DSM function provides backwards compatibility on platforms that can run 
legacy operating
systems.
Operating systems for two different architectures (e.g., x86 and x64) can be 
installed on a platform.
The firmware cannot distinguish the operating system in time to change the boot 
configuration of
devices. Say for instance, an x86 operating system in non-PAE mode is installed 
on a system. The
x86 operating system cannot access device resource space above 4 GiB. So the 
firmware is required
to configure devices at boot time using addresses below 4 GiB. On the other 
hand, if an x64
operating system is installed on this system, it can access device resources 
above the 4 GiB so it does
not want the firmware to constrain the resource assignment below 4 GiB that the 
firmware
configures at boot time. It is not possible for the firmware to change this by 
the time it boots the
operating system. Ignoring the configurations done by firmware at boot time 
will allow the
operating system to push resource assignment using addresses above 4 GiB for an 
x64 operating
system while constrain it to addresses below 4 GiB for an x86 operating system.

so fundamentally, saying "1" here just means "you can ignore what
firmware configured if you like".


I have a different question though: our CRS etc is based on what
firmware configured. Is that ok? Or is ACPI expected to somehow
reconfigure itself when OS reconfigures devices?
Think it's ok but could not find documentation either way.


> > 
> > Signed-off-by: Jiahui Cen <cenjiahui@huawei.com>
> > ---
> >  hw/pci-host/gpex-acpi.c | 18 ++++++++++++++++--
> >  1 file changed, 16 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/pci-host/gpex-acpi.c b/hw/pci-host/gpex-acpi.c
> > index 11b3db8f71..c189306599 100644
> > --- a/hw/pci-host/gpex-acpi.c
> > +++ b/hw/pci-host/gpex-acpi.c
> > @@ -112,10 +112,24 @@ static void acpi_dsdt_add_pci_osc(Aml *dev)
> >      UUID = aml_touuid("E5C937D0-3553-4D7A-9117-EA4D19C3434D");
> >      ifctx = aml_if(aml_equal(aml_arg(0), UUID));
> >      ifctx1 = aml_if(aml_equal(aml_arg(2), aml_int(0)));
> > -    uint8_t byte_list[1] = {1};
> > -    buf = aml_buffer(1, byte_list);
> > +    uint8_t byte_list[] = {
> > +                0x1 << 0 /* support for functions other than function 0 */ 
> > |
> > +                0x1 << 5 /* support for function 5 */
> > +                };
> > +    buf = aml_buffer(ARRAY_SIZE(byte_list), byte_list);
> >      aml_append(ifctx1, aml_return(buf));
> >      aml_append(ifctx, ifctx1);
> > +
> > +    /* PCI Firmware Specification 3.1
> > +     * 4.6.5. _DSM for Ignoring PCI Boot Configurations
> > +     */
> > +    /* Arg2: Function Index: 5 */
> > +    ifctx1 = aml_if(aml_equal(aml_arg(2), aml_int(5)));
> > +    /* 0 - The operating system must not ignore the PCI configuration that
> > +     *     firmware has done at boot time.
> > +     */
> > +    aml_append(ifctx1, aml_return(aml_int(0)));
> > +    aml_append(ifctx, ifctx1);
> >      aml_append(method, ifctx);
> >  
> >      byte_list[0] = 0;