Re: [PATCH v1] PCI: endpoint: Skip upper halves of 64-bit BARs during search

[Niklas Cassel]

On Wed, Oct 21, 2026 at 12:46:03PM +0200, Niklas Cassel wrote:
> On Wed, Oct 21, 2026 at 01:36:44PM +0530, Manikanta Maddireddy wrote:
> > pci_epc_get_next_free_bar() skips the upper half of a 64-bit BAR only
> > when it is the starting BAR. If the search subsequently passes a
> > reserved or disabled 64-bit BAR, it can return its upper half as an
> > independent BAR because that slot has a default programmable descriptor.
> > 
> > For example, Tegra exposes a programmable 64-bit BAR0 and reserved
> > 64-bit BAR2 and BAR4. A search starting at BAR1 skips BAR1 and BAR2,
> > then incorrectly returns BAR3. The next search can similarly return
> > BAR5, causing the EPF test driver to allocate and program BARs that
> > belong to the reserved hardware windows.
> 

> 12a22fb38cbb ("PCI: tegra194: Expose BAR2 (MSI-X) and BAR4 (DMA) as
> 64-bit BAR_RESERVED").
> 
> 
> I'm fine with this patch, but I think you need to rephrase the kdoc
> to reflect this new reality, because currently the kdoc is confusing/
> not in line with the 'new' meaning of BAR_RESERVED, which can contain
> MSI-X table etc.

To clarify, I can see that you updated the definition in:
27ce1d8ecb9b ("PCI: endpoint: Allow only_64bit on BAR_RESERVED")


But, IMO it is still not super clear.

Perhaps we should have mentioned explicitly that only_64bit is
also allowed on a BAR_RESERVED, if that reserved BAR is 64-bit.
(Since that use case is different from what the kdoc currently
says.)


I also think that this patch needs a Fixes tag with either:
27ce1d8ecb9b ("PCI: endpoint: Allow only_64bit on BAR_RESERVED")
or
12a22fb38cbb ("PCI: tegra194: Expose BAR2 (MSI-X) and BAR4 (DMA) as
64-bit BAR_RESERVED")


Kind regards,
Niklas