On Fri, 2005-08-26 at 11:59 -0700, Linux Kernel Mailing List wrote:
> tree d8b7aaaec93de93841b46e8e05a3b454d05bd357
> parent 26aad69e3dd854abe9028ca873fb40b410a39dd7
> author Linus Torvalds <[email protected]> Sat, 27 Aug 2005 00:49:22 -0700
> committer Linus Torvalds <[email protected]> Sat, 27 Aug 2005 00:49:22 -0700
>
> Ignore disabled ROM resources at setup
>
> Writing even a disabled value seems to mess up some matrox graphics
> cards. It may be a card-related issue, but we may also be writing
> reserved low bits in the result.
>
> This was a fall-out of switching x86 over to the generic PCI resource
> allocation code, and needs more debugging. In particular, the old x86
> code defaulted to not doing any resource allocations at all for ROM
> resources.
>
> In the meantime, this has been reported to make X happier by Helge
> Hafting <[email protected]>.
This "fix" also seems to break all powermac laptops around :( In fact,
it might break any user of pci_map_rom() as it exposes a bug in that
function.
The problem is that their firmware doesn't assign a ROM resource as they
have no ROM on the video chip (like most laptops). radeonfb and aty128fb
among others will call pci_map_rom() to try to find an x86 BIOS ROM with
some config tables in it.
pci_map_rom "sees" that the resource is unassigned by testing the parent
pointer, and calls pci_assign_resource() which, with this new patch,
will do nothing.
Unfortunately, pci_map_rom will not notice this failure, and will
happily ioremap & access the bogus resource, thus causing the crash.
I'll come up with a fix for pci_map_rom later today.
While looking there, I also noticed pci_map_rom_copy() stuff and I'm
surprised it was ever accepted in the tree. While I can understand that
we might need to keep a cached copy of the ROM content (due to cards
like matrox who can't enable both the ROM and the BARs among other
issues), the whole idea of whacking a kernel virtual pointer in the
struct resource->start of the ROM bar is just too disgusting for words
and will probably cause "intersting" side effects in /proc, sysfs and
others... Shouldn't we just have a pointer in pci_dev for the optional
"ROM cache" instead ?
Ben.
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