Re: [PATCH 7/9] PCI: endpoint: pci-epf-test: Advertise reserved BARs

[Frank Li <Frank.li@nxp.com>]

On Wed, Feb 18, 2026 at 11:43:27AM +0100, Niklas Cassel wrote:
> On Tue, Feb 17, 2026 at 06:02:55PM -0500, Frank Li wrote:
> > On Tue, Feb 17, 2026 at 10:27:13PM +0100, Niklas Cassel wrote:
> > > Advertise reserved BARs as reserved in the Capabilities register,
> > > such that the host side driver will be able to skip reserved BARs.
> > >
> > > Signed-off-by: Niklas Cassel <cassel@kernel.org>
> > > ---
> > >  drivers/pci/endpoint/functions/pci-epf-test.c | 24 +++++++++++++++++++
> > >  1 file changed, 24 insertions(+)
> > >
> > > diff --git a/drivers/pci/endpoint/functions/pci-epf-test.c b/drivers/pci/endpoint/functions/pci-epf-test.c
> > > index 0cb7af0919dc..4c7e42fe5d8e 100644
> > > --- a/drivers/pci/endpoint/functions/pci-epf-test.c
> > > +++ b/drivers/pci/endpoint/functions/pci-epf-test.c
> > > @@ -64,6 +64,12 @@
> > >  #define CAP_MSIX			BIT(2)
> > >  #define CAP_INTX			BIT(3)
> > >  #define CAP_SUBRANGE_MAPPING		BIT(4)
> > > +#define CAP_BAR0_RESERVED		BIT(5)
> > > +#define CAP_BAR1_RESERVED		BIT(6)
> > > +#define CAP_BAR2_RESERVED		BIT(7)
> > > +#define CAP_BAR3_RESERVED		BIT(8)
> > > +#define CAP_BAR4_RESERVED		BIT(9)
> > > +#define CAP_BAR5_RESERVED		BIT(10)
> > >
> > >  #define PCI_EPF_TEST_BAR_SUBRANGE_NSUB	2
> > >
> > > @@ -1106,6 +1112,24 @@ static void pci_epf_test_set_capabilities(struct pci_epf *epf)
> > >  	    epf_test->epc_features->subrange_mapping)
> > >  		caps |= CAP_SUBRANGE_MAPPING;
> > >
> > > +	if (epf_test->epc_features->bar[BAR_0].type == BAR_RESERVED)
> > > +		caps |= CAP_BAR0_RESERVED;
> >
> > Is it BAR_DISABLE? suppose BAR_RESERVED redefine as hardware MMIO mapped
> > bar
>
>
> A BAR that is defined as BAR_DISABLE will always be disabled by the EPC
> driver, so the host side driver will not see the BAR in the first place.
>
> If you try to run pci_endpoint_test against a disabled BAR, the size will
> be zero, and pci_endpoint_test will return -ENODATA:
> https://github.com/torvalds/linux/blob/v6.19/drivers/misc/pci_endpoint_test.c#L300-L302
>
> and the pci_endpoint selftest will print SKIP for that test case.
>
>
> BAR_RESERVED is describing a BAR that has hardware backed resources, e.g. eDMA
> registers, iATU registers, MSI-X table. These BARs are never disabled by an
> EPC driver by default. See the kdoc for these enum values here:
> https://lore.kernel.org/linux-pci/20260217212707.2450423-15-cassel@kernel.org/
>
>
> Thus, we need to tell pci_endpoint_test that these reserved BARs (which are
> not disabled) has to be skipped, because if we perfrom READ/WRITE tests
> against these BARs, bad things will happen. E.g. if you write to a BAR that
> exposes iATU registers, you will clear/overwrite the current inbound addresss
> translation configured by the endpoint.

I see. it actually means skip bar test. is CAP_SKIP_BAR<n>_TEST better?

Frank
>
>
> Kind regards,
> Niklas