Re: [PATCH v2 1/2] PCI: endpoint: Skip upper halves of 64-bit BARs during search

[Frank Li]

On Mon, Nov 02, 2026 at 04:53:05PM +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.
>
> Check each candidate's preceding descriptor inside the search loop so
> upper halves are skipped throughout the search. With the Tegra layout,
> BAR0 is the only available BAR and subsequent searches return NO_BAR.
>
> Fixes: 27ce1d8ecb9b ("PCI: endpoint: Allow only_64bit on BAR_RESERVED")
> Signed-off-by: Manikanta Maddireddy <mmaddireddy@xxxxxxxxxx>
> ---

Reviewed-by: Frank Li <Frank.Li@xxxxxxx>

> Changes V1 -> V2:
> - Add Fixes: 27ce1d8ecb9b ("PCI: endpoint: Allow only_64bit on BAR_RESERVED")
>   following Niklas Cassel's review.
> - Rebase onto the current PCI main-based patch stack.
> - No code changes from v1.
>
>  drivers/pci/endpoint/pci-epc-core.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/pci/endpoint/pci-epc-core.c b/drivers/pci/endpoint/pci-epc-core.c
> index 831b40458dcd..8d0df9fc1df9 100644
> --- a/drivers/pci/endpoint/pci-epc-core.c
> +++ b/drivers/pci/endpoint/pci-epc-core.c
> @@ -98,11 +98,11 @@ enum pci_barno pci_epc_get_next_free_bar(const struct pci_epc_features
>  	if (!epc_features)
>  		return BAR_0;
>
> -	/* If 'bar - 1' is a 64-bit BAR, move to the next BAR */
> -	if (bar > 0 && epc_features->bar[bar - 1].only_64bit)
> -		bar++;
> -
>  	for (i = bar; i < PCI_STD_NUM_BARS; i++) {
> +		/* Skip the upper half of a 64-bit BAR. */
> +		if (i > 0 && epc_features->bar[i - 1].only_64bit)
> +			continue;
> +
>  		/* If the BAR is not reserved or disabled, return it. */
>  		if (epc_features->bar[i].type != BAR_RESERVED &&
>  		    epc_features->bar[i].type != BAR_DISABLED)
> --
> 2.34.1
>