linux-kernel - Re: [RFC PATCH v2 19/27] PCI: dwc: ep: Cache MSI outbound iATU mapping

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Message-ID: <mb2tkza65fj77i3cjs7t2lrcrxnlesn7aibf46zq3c3fahjp7i@2hcziakdeo5s>
Date: Wed, 3 Dec 2025 17:30:52 +0900
From: Koichiro Den <den@...inux.co.jp>
To: Niklas Cassel <cassel@...nel.org>
Cc: ntb@...ts.linux.dev, linux-pci@...r.kernel.org, 
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org, Frank.Li@....com, mani@...nel.org, 
	kwilczynski@...nel.org, kishon@...nel.org, bhelgaas@...gle.com, corbet@....net, 
	vkoul@...nel.org, jdmason@...zu.us, dave.jiang@...el.com, allenbh@...il.com, 
	Basavaraj.Natikar@....com, Shyam-sundar.S-k@....com, kurt.schwemmer@...rosemi.com, 
	logang@...tatee.com, jingoohan1@...il.com, lpieralisi@...nel.org, robh@...nel.org, 
	jbrunet@...libre.com, fancer.lancer@...il.com, arnd@...db.de, pstanner@...hat.com, 
	elfring@...rs.sourceforge.net, Damien Le Moal <dlemoal@...nel.org>
Subject: Re: [RFC PATCH v2 19/27] PCI: dwc: ep: Cache MSI outbound iATU
 mapping

On Tue, Dec 02, 2025 at 07:32:31AM +0100, Niklas Cassel wrote:
> On Sun, Nov 30, 2025 at 01:03:57AM +0900, Koichiro Den wrote:
> > dw_pcie_ep_raise_msi_irq() currently programs an outbound iATU window
> > for the MSI target address on every interrupt and tears it down again
> > via dw_pcie_ep_unmap_addr().
> > 
> > On systems that heavily use the AXI bridge interface (for example when
> > the integrated eDMA engine is active), this means the outbound iATU
> > registers are updated while traffic is in flight. The DesignWare
> > endpoint spec warns that updating iATU registers in this situation is
> > not supported, and the behavior is undefined.
> 
> Please reference a specific section in the EP databook, and the specific
> EP databook version that you are using.

Ok, the section I was referring to in the commit message is:

DW EPC databook 5.40a - 3.10.6.1 iATU Outbound Programming Overview
"Caution: Dynamic iATU Programming with AXI Bridge Module You must not update
the iATU registers while operations are in progress on the AXI bridge slave
interface."

> 
> This patch appears to address quite a serious issue, so I think that you
> should submit it as a standalone patch, and not as part of a series.
> 
> (Especially not as part of an RFC which can take quite long before it is
> even submitted as a normal (non-RFC) series.)

Makes sense, thank you for the guidance.

Koichiro

> 
> 
> Kind regards,
> Niklas