linux-kernel - Re: [PATCH v5 08/12] PCI: imx6: Config look up table(LUT) to support MSI ITS and IOMMU for i.MX95

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Date: Tue, 4 Jun 2024 11:47:58 -0400
From: Frank Li <Frank.li@....com>
To: Marc Zyngier <maz@...nel.org>
Cc: Robin Murphy <robin.murphy@....com>, Bjorn Helgaas <helgaas@...nel.org>,
	Richard Zhu <hongxing.zhu@....com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	NXP Linux Team <linux-imx@....com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-pci@...r.kernel.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
	devicetree@...r.kernel.org, Will Deacon <will@...nel.org>,
	Joerg Roedel <joro@...tes.org>, Jason Gunthorpe <jgg@...pe.ca>,
	Alyssa Rosenzweig <alyssa@...enzweig.io>
Subject: Re: [PATCH v5 08/12] PCI: imx6: Config look up table(LUT) to support
 MSI ITS and IOMMU for i.MX95

On Tue, Jun 04, 2024 at 04:25:51PM +0100, Marc Zyngier wrote:
> On Mon, 03 Jun 2024 22:04:23 +0100,
> Frank Li <Frank.li@....com> wrote:
> > 
> > iommu may share one stream id for multi-devices. but ITS MSI can't. each
> > device's MSI index start from 0. It needs difference stream id for each
> > device.
> 
> That's not quite true. We go through all sort of hoops to find about
> device aliasing on PCI and allow devices that translate into the same
> DID to get MSIs.

Could you please point me the code location? I remember I met error when I
try to enable MSI for EP support one year ago.

https://lore.kernel.org/imx/20221124055036.1630573-1-Frank.Li@nxp.com/

I remember that it is failure try to allocate more irqs with the same DID. 

Frank

> 
> Of course, just like the IOMMU, you lose any form of isolation, but
> you get what you pay for.

Anyways, if there are one quirk in PCI system, bridge driver can detect
PCI devices add/remove. it will be better if assign stream ID as need,
compared with static allocate.

> 
> 	M.
> 
> -- 
> Without deviation from the norm, progress is not possible.