Re: s3 doesn't work on non i386/amd64

[T <bobs%thelibertytree.org@localhost>]

On Tue, 15 Nov 2022 07:22:37 -0000 (UTC), T wrote:

> Hello,
> Xorg stopped working for me after upgrading from NetBSD 8.x to 9.x and
> hasn't worked since, it always segfaults. There is the Xorg log output
> posted on the port-prep mailing list, although it does not really
> provide any specific clues to the root cause. I've recently used GDB on
> Xorg with debug sets and believe the problem was introduced when some
> changes were made to the s3 driver and a few related files. The
> backtrace output is also on the port-prep mailing list.
> 
> The flow is:
> vgaHWSetStdFuncs(hwp) ->
> ci_legacy_open_io(hwp->dev, 0, 64 * 1024) ->
> !pci_sys->methods->open_legacy_io(ret, dev, base, size) -> resolves to:
> pci_device_netbsd_open_legacy_io(...)
> 
> ...
=========================================================================
> 
> This always returns a NULL handle because the system I'm using is not
> i386 or amd64. This causes this to segfault:
> vgaHWGetIOBase(hwp) ->
> hwp->readMiscOut(hwp) -> resolves to:
> stdReadMiscOut(vgaHWPtr hwp) -> which calls:
> pci_io_read8(hwp->io, VGA_MISC_OUT_R) ->
> segfault, as hwp->io is 0x0
> 
> ...
=========================================================================
> 
> It would seem that pci_device_netbsd_open_legacy_io(...) would need to
> be modified to allow for non x86 systems to use the s3 driver.

I received some feedback in IRC:

"That function is for getting a port IO handle. Port IO itself is x86 
centric. On archs other than x86 there generally is not a concept of port 
IO at all, the function returns NULL if it can't get access to port IO, 
and that can only happen via an IOPL call so when on a non-x86 arch it 
should fail. Well, there's probably other ways to access the PCI I/O 
address space. I think it's usually mappable, and netbsd probably uses it 
for something. I'm not sure what options userspace would have for 
accessing it in that case though."

"vgaHW.c is missing error branches in the event pci_legacy_open_io fails"