linux-kernel - Re: [PATCH RFC 2/2] iommu/arm-smmu-v3: Bypass SID0 for NXP i.MX95

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Message-ID: <20241015124723.GI1825128@ziepe.ca>
Date: Tue, 15 Oct 2024 09:47:23 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Pranjal Shrivastava <praan@...gle.com>
Cc: "Peng Fan (OSS)" <peng.fan@....nxp.com>, Will Deacon <will@...nel.org>,
	Robin Murphy <robin.murphy@....com>, Joerg Roedel <joro@...tes.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Joy Zou <joy.zou@....com>,
	linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Peng Fan <peng.fan@....com>
Subject: Re: [PATCH RFC 2/2] iommu/arm-smmu-v3: Bypass SID0 for NXP i.MX95

On Tue, Oct 15, 2024 at 08:13:28AM +0000, Pranjal Shrivastava wrote:

> Umm.. this was specific for rmr not a generic thing. I'd suggest to
> avoid meddling with the STEs directly for acheiving bypass. Playing
> with the iommu domain type could be neater. Perhaps, modify the
> ops->def_domain_type to return an appropriate domain?

Yeah, that is the expected way, to force the def_domain_type to
IDENTITY and refuse to attach a PAGING/BLOCKED domain.

If this is a common thing we could have the core code take on more of
the job.

Jason