Re: [PATCH v2 1/2] PCI: Take multifunction devices into account when distributing resources

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Nov 22, 2022 at 11:45:41AM +0000, Jonathan Cameron wrote:
> On Tue, 22 Nov 2022 08:42:58 +0200
> Mika Westerberg <mika.westerberg@linux.intel.com> wrote:
> > On Mon, Nov 21, 2022 at 04:45:48PM -0600, Bjorn Helgaas wrote:
> > > IIUC, the summary is this:
> > > 
> > >   00:02.0 bridge window [mem 0x10000000-0x102fffff] to [bus 01-02]
> > >   01:02.0 bridge window [mem 0x10000000-0x100fffff] to [bus 02]
> > >   01:03.0 NIC BAR [mem 0x10200000-0x1021ffff]
> > >   01:04.0 NIC BAR [mem 0x10220000-0x1023ffff]
> > >   02:05.0 NIC BAR [mem 0x10080000-0x1009ffff]
> > > 
> > > and it's the same with and without the current patch.
> > > 
> > > Are all these assignments done by BIOS, or did Linux update them?  
> > 
> > > Did we exercise the same "distribute available resources" path as in
> > > the PCIe case?  I expect we *should*, because there really shouldn't
> > > be any PCI vs PCIe differences in how resources are handled.  This is
> > > why I'm not comfortable with assumptions here that depend on PCIe.
> > > 
> > > I can't tell from Jonathan's PCIe case whether we got a working config
> > > from BIOS or not because our logging of bridge windows is kind of
> > > poor.  
> > 
> > This is ARM64 so there is no "BIOS" involved (something similar though).
> 
> It's EDK2 in my tests  - so very similar to other arch.
> Possible to boot without though and rely on DT, but various things don't
> work yet...

Doesn't matter whether it's BIOS/EFI/EDK2/etc, the question was really
whether anything has programmed BARs and windows before Linux gets
started.

> From liberal distribution of printk()s it seems that for PCI bridges
> pci_bridge_resources_not_assigned() is false, but for PCI express
> example it is true.  My first instinct is quirk of the EDK2 handling? 
> I'll have a dig, but I'm not an expert in EDK2 at all, so may not get
> to the bottom of this.

I don't know what pci_bridge_resources_not_assigned() is.

> Ultimately it seems that when the OS takes over the prefetchable memory
> resources are not configured for the PCIe case, but are for the PCI case.
> So we aren't currently walking the new code for PCI.

Whatever the reason for this is, it doesn't sound like something Linux
should assume or rely on.

Bjorn