Re: 64-bit pci bar on a 32-bit kernel

[Jeff Garzik <jgarzik@pobox.com>]

Terence Ripperda wrote:
> Hello,
> 
> we've gotten a customer report of a problem whereby our framebuffer is
> not visible through the kernel. the kernel data structures in struct
> pci_dev have bar1 (our framebuffer) set to 0, and the bar does not
> appear in /proc/pci.
> 
> after a little investigation, it appears that the bios allocated a
> 64-bit bar in pci config space. our gpu claims 64-bit support in pci
> config space and the cpu is an em64t. but the customer is running a
> 32-bit kernel on the em64t, which is a reasonable thing to do. it
> turns out the pci driver does not like 64-bit bars on a 32-bit kernel
> and prints out the following messages during boot:
> 
> PCI: PCI BIOS revision 2.10 entry at 0xf0031, last bus=5
> PCI: Using configuration type 1
> PCI: Probing PCI hardware
> PCI: Probing PCI hardware (bus 00)
> PCI: Ignoring BAR0-3 of IDE controller 00:1f.1
> PCI: Unable to handle 64-bit address space for
> PCI: Unable to handle 64-bit address space for
> PCI: Unable to handle 64-bit address for device 03:00.0
> PCI: Unable to handle 64-bit address space for
> 
> Is this an expected problem? Is there any reason why the 32-bit kernel
> couldn't handle 64-bit bars?

hmmm, that's a good question.

I wonder if ioremap() even supports 64-bit addresses on 32-bit platforms?

64-bit MMIO is a bit different from 64-bit DMA; though its still only 
page tables...

	Jeff