Re: [edk2-platforms PATCH 3/6] Marvell: Armada7k8kPciHostBridgeLib: Remove ECAM base limitation

["Ard Biesheuvel" <ardb@kernel.org>]

On Mon, 2 Aug 2021 at 19:00, Marcin Wojtas <mw@semihalf.com> wrote:
>
> Hi Ard,
>
> pon., 2 sie 2021 o 10:43 Ard Biesheuvel <ardb@kernel.org> napisał(a):
> >
> > On Mon, 2 Aug 2021 at 07:01, Marcin Wojtas <mw@semihalf.com> wrote:
> > >
> > > On CN913x-based platforms it is possible to have up to 9 PCIE
> > > root complexes. In such case it may be necessary to configure
> > > more configuration spaces with smaller bus count, so that
> > > to fit the memory layout constraints. For that purpose remove
> > > forcing ECAM base to be divisible by SIZE_256MB.
> > >
> >
> > There is one subtlety here that we need to take into account: IIUC,
> > PCIe requires that the ECAM start address of bus N equals N MB modulo
> > 256 MB. In other words, if your ECAM range lives at 1 GB + 128 MB, the
> > bus range has to start at bus 128.
> >
> > I think OSes are usually quite lax about this, but it is something to
> > double check regardless, even for existing platforms
> >
>
> I tested a wide range of OSs (various Linux distributions, Win10 PE,
> FreeBSD, OpenBSD and of course EDK2) and with 7 ECAMs, of which 6 are
> squeezed within 256MB memory chunk together with their mmio32 and no
> issue was observed. Moreover, if you recall, contrary to the EDK2,
> where the full bus number is used, in ACPI we expose a single 1MB
> space with the ECAM base address aligned to 0x8000.
>

Ah yes, I had forgotten about that hack :-)

> Do you wish to change the assertion in EDK2 instead of removing?
>

No worries - if all those OSes are fine with this, I don't see a point
in being pedantic. I will note, however, that you can still comply
with this requirement by changing the bus ranges: each RC only uses a
single bus, but that bus number could be (ECAM base address / 1M) %
256


> >
> > > Signed-off-by: Marcin Wojtas <mw@semihalf.com>
> > > ---
> > >  Silicon/Marvell/Armada7k8k/Library/Armada7k8kPciHostBridgeLib/PciHostBridgeLibConstructor.c | 1 -
> > >  1 file changed, 1 deletion(-)
> > >
> > > diff --git a/Silicon/Marvell/Armada7k8k/Library/Armada7k8kPciHostBridgeLib/PciHostBridgeLibConstructor.c b/Silicon/Marvell/Armada7k8k/Library/Armada7k8kPciHostBridgeLib/PciHostBridgeLibConstructor.c
> > > index 067e57a2dc..87e57aeae3 100644
> > > --- a/Silicon/Marvell/Armada7k8k/Library/Armada7k8kPciHostBridgeLib/PciHostBridgeLibConstructor.c
> > > +++ b/Silicon/Marvell/Armada7k8k/Library/Armada7k8kPciHostBridgeLib/PciHostBridgeLibConstructor.c
> > > @@ -219,7 +219,6 @@ Armada7k8kPciHostBridgeLibConstructor (
> > >      PcieController = &(BoardPcieDescription->PcieControllers[Index]);
> > >
> > >      ASSERT (PcieController->PcieBusMin == 0);
> > > -    ASSERT (PcieController->ConfigSpaceAddress % SIZE_256MB == 0);
> > >
> > >      if (PcieController->HaveResetGpio == TRUE) {
> > >        /* Reset PCIE slot */
> > > --
> > > 2.29.0
> > >