On Thu, 28 Apr 2005 16:39:13 +1000
Benjamin Herrenschmidt <[email protected]> wrote:
> On Wed, 2005-04-27 at 22:37 -0700, David S. Miller wrote:
> > On Wed, 27 Apr 2005 23:33:11 -0600
>
> > The 'offset' argument is defined to be page aligned
> > when passed to mmap().
>
> mmap API in general is defined to only ever deal with page aligned
> parameters & return values no ?
Yes.
> Except from that page alignment thing ... which is the root of the
> problem.
You can hide all of those problems in libpci.a or whatever.
You page align the offset, but pass back to the user a pointer
with his sub-page offset applied to it.
The kernel wants pages, so just give it pages :-)
> > I hate to say this, but the largest consumer of this stuff is the
> > X server, so we really need to force ourselves to work in parallel
> > on clean X server support.
>
> Cleaning X.org is my goal, this is why I'm trying to clean the kernel
> side first :) I'm also working separately on the problem of VGA access
> arbitration (We'll probably do a joint session with the desktop summit
> an the kernel summit about those issue).
Yeah, that one is all about enabling VGA forwarding in the bridges.
Taking out all of the resource garbage in the X server, and replacing
it with properly synchronized calls in the kernel for mapping ROMs
and changing the current VGA forwarding seems to be the way to go.
> > On many platforms some kind of "side effect" bit in the PTE
> > determine if store buffer compression can happen in the processor.
> > We'd want to not set such a bit for things like frame-buffers and
> > the like.
>
> Yes, and I think that pretty much match with PCI devices exposing a
> "prefetchable" BAR, don't you agree ?
Some scsi controllers have prefetchable set in their normal
register BARs. The sym53c8xx does if I remember correctly.
Anyways, what I'm trying to say is that blinding turning prefetchable
BAR into "don't set side effect bit in PTE" might not be so wise.
I really think it's a userlevel decision. That's where all the ioctl()
garbage came from for the /proc/bus/pci mmap() stuff. It was for chossing
IO vs MEM space, and also for setting these kinds of mapping attributes.
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