Re: [PATCH] PCI: endpoint: pci-epf-test: Roll back BAR mapping when subrange setup fails

[Christian Bruel]

On 3/17/26 10:24, Niklas Cassel wrote:
> On Tue, Mar 17, 2026 at 10:13:52AM +0100, Christian Bruel wrote:
> > Tested-by: Christian Bruel <christian.bruel@xxxxxxxxxxx>
> >
> > with the DISABLE BAR dependency
> > https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/commit/?h=endpoint&id=33642e9e36dc084e4fc9245a266c9843bc8303b9
> >
> > I will need to update the pci_epc_features after the merge.
>
> I don't think you should update pci_epc_features just to be able to test
> the inbound submapping feature.
>
> As I said before, I think a better option would to ensure that the test is
> skipped instead of returning failure, for SoCs with too few inbound iATUs.

So we will need to add a SKIP ENOSPC case in TEST_F(pci_ep_bar, 
BAR_SUBRANGE_TEST)

Note this will be equivalent to set .subrange_mapping to false in the 
pci_epc_features. But I agree, it only pertains to the epf test driver, 
not all epf drivers. Touching pci_epc_features is not a good idea

> A real EPF driver (not the test driver), that wants to run on STM32, and
> wants to use inbound submapping feature, can simply ensure that it does not
> enable all BARs (the test driver obviously enables all BARs, since it wants
> to test all BARs). That way, that EPF driver will be able to use multiple
> iATUs for a single BAR (as required by this new feature).
>
> This works because all BARs are disabled by default. An EPF driver has to
> enable the BARs it wants to use. (E.g. nvmet-pci-epf only enables BAR0.)
>
>
> > A more general question: I don't understand why only the STM32 is impacted.
> > It seems that all targets, even those with 6 IB iATU entries, should ensure
> > that one BAR is disabled to handle subranges.
>
> I can't speak for every SoC, but looking at dmesg:
> rockchip-dw-pcie a40000000.pcie-ep: iATU: unroll T, 16 ob, 16 ib, align 64K, limit 8G
>
> rk3588 has 16 inbound windows.
>
> Probably most SoCs have more than 6 ib windows?

Yes, probably, thank you

Cheers

Christian

> Kind regards,
> Niklas