Re: pci overmapping

[Scott Wood <scottwood@freescale.com>]

On 05/02/2013 01:09:53 PM, Sethi Varun-B16395 wrote:
>=20
>=20
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Thursday, May 02, 2013 10:44 PM
> > To: Yoder Stuart-B08248
> > Cc: galak@kernel.crashing.org; Sethi Varun-B16395; linuxppc-
> > dev@lists.ozlabs.org
> > Subject: Re: pci overmapping
> >
> > On 05/02/2013 12:05:42 PM, Yoder Stuart-B08248 wrote:
> > > Kumar,
> > >
> > > In fsl_pci.c there is a change you made a while back:
> > >   "powerpc/fsl: Setup PCI inbound window based on actual amount of
> > > memory"
> > >
> > > ...and there is this comment in the code:
> > >
> > >     /* PCIe can overmap inbound & outbound since RX & TX are =20
> separated
> > > */
> > >     if (early_find_capability(hose, 0, 0, PCI_CAP_ID_EXP)) {
> > >
> > > You are implying that PCIe can overmap and PCI can't.  Why is
> > > that?   (I'm assuming that 'overmap' means that inbound window
> > > can extend beyond the end of ram.)
> >
> > Shouldn't the concern be whether we're overlapping outbound, not =20
> merely
> > whether we go beyond the end of RAM?
> >
> > And couldn't inbound/outbound overlap be an issue even on PCIe, if
> > there's a PCI bridge underneath it?
> I believe that the overlap problem would be avoided in case of 36 bit =20
> physical support (outbound window address would be high order 36 bit =20
> value), right?

Not necessarily -- it depends on what the bus addresses are, not the =20
host addresses.

-Scott=