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

[Koichiro Den]

On Thu, Mar 05, 2026 at 08:37:35AM +0100, Niklas Cassel wrote:
> 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.
> 
> You could also mention that CX_ATU_MIN_REGION_SIZE can configured to
> a value in range 4 kB to 64 kB, so 1 MB is clearly bogus.
> 
> Reviewed-by: Niklas Cassel <cassel@xxxxxxxxxx>

Thanks for the review and follow-up, Niklas.

(I initially wondered whether the 1MB alignment had some historical reason
behind it, i.e. an intentional or unavoidable hack, which is why I hesitated to
add a Fixes tag. But I agree that it is bogus today.)

Best regards,
Koichiro