From: Rao G

Date: 2022-01-28 21:08

To: Michael Brown

CC: devel

Subject: Re: [edk2-devel] Read SPI BAR offset 0x10 throwing processor exception

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@...> 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