Re: [PATCH] PCI: dwc: rcar-gen4: Use 4K EPC BAR alignment

[Niklas Cassel <cassel@kernel.org>]

On Thu, Mar 05, 2026 at 10:54:39AM +0900, Koichiro Den wrote:
> R-Car S4 Series (R8A779F[4-7]*) uses a 4K minimum iATU region size
> (CX_ATU_MIN_REGION_SIZE = 4K) as per R19UH0161EJ0130 Rev.1.30.
> 
> Update the advertised alignment to 4K, as described in
> commit 2a9a801620ef ("PCI: endpoint: Add support to specify alignment
> for buffers allocated to BARs").
> 
> With the previous 1MB alignment requirement, iATU programming for BAR4
> on this platform often cannot be performed, since a 1MB-aligned target
> address may fall outside the tiny 256B BAR4 window.
> 
> Signed-off-by: Koichiro Den <den@valinux.co.jp>
> ---
>  drivers/pci/controller/dwc/pcie-rcar-gen4.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-rcar-gen4.c b/drivers/pci/controller/dwc/pcie-rcar-gen4.c
> index 3d4a889e38cc..396ef9432299 100644
> --- a/drivers/pci/controller/dwc/pcie-rcar-gen4.c
> +++ b/drivers/pci/controller/dwc/pcie-rcar-gen4.c
> @@ -428,7 +428,7 @@ static const struct pci_epc_features rcar_gen4_pcie_epc_features = {
>  	.bar[BAR_3] = { .type = BAR_RESERVED, },
>  	.bar[BAR_4] = { .type = BAR_FIXED, .fixed_size = 256 },
>  	.bar[BAR_5] = { .type = BAR_RESERVED, },
> -	.align = SZ_1M,
> +	.align = SZ_4K,
>  };
>  
>  static const struct pci_epc_features*
> -- 
> 2.51.0
> 

CX_ATU_MIN_REGION_SIZE has
Label: Minimum Size of Translation Region
Value Range: 4, 8, 16, 32, 64 kB
Default: 64 kB

1 MB is larger than 64 kB, so it is clearly wrong.


Kind regards,
Niklas