Hi Michael,

SpiInstance->PchSpiBase = MmPciBase (
                              DEFAULT_PCI_BUS_NUMBER_PCH,
                              PCI_DEVICE_NUMBER_PCH_SPI,
                              PCI_FUNCTION_NUMBER_PCH_SPI
                              );
DEBUG ((DEBUG_INFO, "PchSpiBase at 0x%x\n", SpiInstance->PchSpiBase));
>> returns PchSpiBase as 0xC00FD000 (Bus 0 Dev 1F Func 0)

ScSpiBar0 = MmioRead32 (SpiInstance->PchSpiBase +
PCI_BASE_ADDRESSREG_OFFSET) & 0xFFFFF000;
>> this should return value at 0xC00FD010

Hope it appears to be a standard code and accessing through MMIO library
should work

Thanks
Ranga

On Fri, Jan 28, 2022 at 12:59 PM Michael Brown <mcb30@ipxe.org> wrote:

> On 28/01/2022 12:47, Rao G wrote:
> > Attempting to Read SPIBAR 0x10 from BUS 0 Dev 1F Func 5
> >
> >  >>
> > ScSpiBar0 = MmioRead32 (SpiInstance->PchSpiBase +
> > PCI_BASE_ADDRESSREG_OFFSET) & 0xFFFFF000;
> >  >>
> >
> > The above code is throwing exception
> >
> > PchSpiBase at 0xC00FD000
> > !!!! X64 Exception Type - 0E(#PF - Page-Fault)  CPU Apic ID - 00000000
> !!!!
> > ExceptionData - 0000000000000000  I:0 R:0 U:0 W:0 P:0 PK:0 SS:0 SGX:0
> > RIP  - 00000000771903D0, CS  - 0000000000000038, RFLAGS -
> 0000000000010046
> >
> >  From the shell the value at offset 0x10 is 0xFE010000
> >
> > Any clues on why the processor is throwing exception while accessing the
> > value PchSpiBase+0x10 ?
>
> PCI_BASE_ADDRESSREG_OFFSET is an offset within PCI configuration space.
>   It looks as though you are trying to use an MMIO access to read from
> PCI configuration space, which is not a valid thing to do.
>
> I suspect you may want to use EFI_PCI_IO_PROTOCOL.Pci.Read() instead.
>
> HTH,
>
> Michael
>