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Date: Thu, 5 Mar 2026 08:37:35 +0100
From: Niklas Cassel <cassel@kernel.org>
To: Koichiro Den <den@valinux.co.jp>
Cc: Marek Vasut <marek.vasut+renesas@gmail.com>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= <kwilczynski@kernel.org>,
	Manivannan Sadhasivam <mani@kernel.org>,
	Rob Herring <robh@kernel.org>, Bjorn Helgaas <bhelgaas@google.com>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Magnus Damm <magnus.damm@gmail.com>, linux-pci@vger.kernel.org,
	linux-renesas-soc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] PCI: dwc: rcar-gen4: Use 4K EPC BAR alignment
Message-ID: <aakyvxxFnBkl4io5@ryzen>
References: <20260305015439.1529006-1-den@valinux.co.jp>
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In-Reply-To: <20260305015439.1529006-1-den@valinux.co.jp>

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@kernel.org>