On Sep 6, 2012, at 8:48 AM, Bhavana Brar wrote:
> Hi,
> I'm using the UDK2010 package and I was able to read/write the PCI config
> space by using the PCIReadCf8/WriteCf8 functions (PciLib/PciExpresslib). I
> was also able to access the config space using the memory mapped PCI
> functions ( memread8/memwrite8) etc.
> However, if I try and get the base address ( using one of the helper
> functions defined in the Lib) and then add the offset to it and dereference
> this , I don't read the expected value. Is there any virtual mapping being
> done or to be done for memory mapped access of PCI Config space in order for
> this direct method to work.
>
> I'm trying to do the above steps in an efi application that is loaded via the
> Shell prior to the OS booting.
>
Don't use the low level library functions, as they are for the low level
platform firmware for early init. To make PCI Express work you need to know a
base address that can vary. I will also point out that the PCI config space
access mechanism is not standardized in the PCI spec. How do you do CF8/CFC on
an ARM platform that does not have IO space?
>From an application, or even and EFI Driver, the PCI IO Protocol is used to
>access PCI Config space. There is a chapter on PCI in the UEFI spec that you
>will find helpful.
Thanks,
Andrew
> Thanks
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