Re: [PATCH 0/4] PCI: endpoint: Add BAR_DISABLED support to PCI endpoint framework

[Niklas Cassel <cassel@kernel.org>]

On Tue, Feb 17, 2026 at 11:24:40AM +0530, Manikanta Maddireddy wrote:
> When Tegra194 runs in PCIe endpoint mode, BAR1–BAR5 are marked BAR_RESERVED so the
> EPF does not allocate backing memory. The host-side pci_endpoint_test driver
> still ioremaps all enabled BARs and runs BAR read/write tests on them. Writing to
> BAR2 (MSI-X table) or BAR4 (DMA registers) corrupts controller state and breaks
> CONSECUTIVE_BAR_TEST. A prior fix reset all BARs in the EPC .init(), so only
> BAR0 was visible to the host—tests passed but 64-bit BAR 2 and BAR 4 were no
> longer available for real use (e.g. host DMA via BAR4).
> 
> This series addresses that by:
> 
> 1) Adding BAR_DISABLED and clarifying BAR_RESERVED in the PCI endpoint core.
>    BAR_RESERVED is used for (a) HW-backed BARs (MSI-X, DMA) that the EPC may
>    leave enabled, and (b) the second register of a 64-bit BAR. BAR_DISABLED is
>    for unused BARs that the EPC must disable in .init() and the EPF must not
>    use. pci_epc_get_next_free_bar() treats both as not free.
> 
> 2) Updating Tegra194 endpoint to use three 64-bit BARs at indices 0, 2, and 4:
>    BAR0+BAR1 for EPF test/data, BAR2+BAR3 for MSI-X table, BAR4+BAR5 for DMA.
>    Only BAR0 and BAR1 are reset in .init(); BAR2/BAR3 and BAR4/BAR5 stay
>    enabled so the host can use MSI-X and DMA.
> 
> 3) Adding a BAR skip mask to pci_endpoint_test so endpoints can skip the
>    destructive BAR test on HW-backed BARs. Tegra EP test data skips BAR1–BAR5
>    (test only BAR0). Adding NVIDIA Tegra194 EP (0x1AD4) and Tegra234 EP (0x229B)
>    to the pci_endpoint_test_tbl so the host driver can bind and run tests
>    without corrupting MSI-X or DMA registers.
> 
> 4) Converting unused BAR_RESERVED to BAR_DISABLED in the Uniphier Pro5 endpoint
>    (BAR4 and BAR5); BAR1 and BAR3 remain BAR_RESERVED as the high halves of
>    64-bit BAR0 and BAR2.
> 
> With this, CONSECUTIVE_BAR_TEST and DMA tests pass while Tegra194 keeps 64-bit
> BAR 2 (MSI-X) and BAR 4 (DMA) enabled for host use.
> 

Hello Manikanta,

There are quite a few things that I think we should implement differently,
please see:
https://lore.kernel.org/linux-pci/20260217212707.2450423-11-cassel@kernel.org/T/#u

I'm not trying to take credit from you, for all I care, feel free to take
over the series and add you Co-developed-by on all the patches.

I just though that it would be easier to explain with code rather than a
lot of back and forth.

Hopefully we can send a V2 that includes more detailed BAR_RESERVED
descriptions, that includes what are behind each BAR_RESERVED (including
sizes of each backing MSI-X table/ATU regs/eDMA regs/whatever) in
pcie-tegra194.c.

I also have a Nvidia Jetson Orin Nano board that I can run in EP mode,
so hopefully we can collaborate to get something merged for v7.1.


Kind regards,
Niklas