RFC: i8259.c cleanup

Geert Uytterhoeven geert at linux-m68k.org
Thu Nov 8 04:17:44 EST 2001

On Wed, 7 Nov 2001 hollis at austin.ibm.com wrote:
> On Wed, Nov 07, 2001 at 10:38:27AM +0100, Gabriel Paubert wrote:
> > The question is why the polling code did not work, subtle timing problems
> > or is the code plain wrong ? I suspect that some 8259 accesses were not
> > serialized well enough.
> I laid out what I saw in
> http://lists.linuxppc.org/linuxppc-workstation/200109/msg00030.html . I could
> be wrong, but our code doesn't seem to match the datasheet very well.
> I think fixing what we have is the least intrusive, but I tried and failed, so
> it was nice to write code that actually worked. :) I guess the PCI intack
> stuff is too varied to be useful though...
> Would you say poking the 8259 directly is more "right" than using 0xbffffff0
> (or equivalent)?

I remember some interrupt-related problems went away on my LongTrail after I
started using the interrupt acknowledge register on the host bridge instead of
the plain i8259 stuff.

> > > The patch also cleans up some whitespace (parts of i8259.c were apparently
> > > copied and pasted from one xterm to another), adds a few comments, and adds
> > > resource_request's for both 8259's.
> >
> > Good, but you should add resource request for the edge/level control
> > register while you are at it (0x4d0/4d1). And you should not require
> > 32 bytes for the 8259. On my boards, the super I/O control port is
> > 0x2e-ox2f.
> That's what I forgot... that code requests directly from ioport_resource,
> which is what gets us into trouble on vgacon. We should use request_region
> instead of request_resource. Unfortunately vgacon is initialized before the
> VMM, and since request_region calls kmalloc we die very early. :/ I didn't
> check to see if that's a problem here.

Or we need a request_resource() that doesn't try to attach to the passed
parent, but walks the list (starting from the passed parent) to hook in at the
right spot. (*)

> The problem with using request_resource(&ioport_resource) in vgacon is that
> our PHB's initialize later, try to reserve their own IO regions (eg
> 0x0->0xffffffff), and fail because vgacon already took 0x3c0 or so.

Yes, so either we have to delay the request_resource() and use the scheme above
(*), or we need a request_resource_and_take_over() call to register the PHB
resources, which reshuffles the already allocated legacy resources.



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds

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