Re: [Bug #12608] 2.6.29-rc powerpc G5 Xorg legacy_mem regression

Benjamin Herrenschmidt
2009-02-05T21:05:44Z

> Is it a really a bug in X, or a misunderstanding between X and
> the kernel as to what existence of the legacy_mem file implies?
>
> I may have got this quite wrong, but to me it appears that X assumes
> that existence of the legacy_mem file implies that it will be useful;
> whereas the kernel thinks it can make the legacy_mem file available,
> even if it cannot be used for mmapping mem - which is its sole purpose?
>
> What if pci_create_legacy_files() were to call some new verification
> routine, and only create the legacy_mem file if it would be usable?
> (But perhaps that cannot be known at the time it needs to be created.)

Well, first X should certainly not -fail- to launch if it fails to map
legacy memory, which is generally not useful anyway. That's where the
bug is. Jesse, did you have a chance to fix that yet or should I give it
a go ?

The second problem is that if I just don't expose the legacy_mem file,
then X has no way to know whether the kernel doesn't support the
interface or whether the HW doesn't support legacy memory access. So X
will fallback to whacking /dev/mem which is even more bogus. At least
that's what I remember from last I looked at that part of X code.

It should be a trivial fix on X side tho.

Cheers,
Ben.