linux-kernel - Re: [PATCH v2 7/7] iommu: Turn iova_cookie to dma-iommu private pointer

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Message-ID: <20250226191818.GB39591@nvidia.com>
Date: Wed, 26 Feb 2025 15:18:18 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: kevin.tian@...el.com, tglx@...utronix.de, maz@...nel.org,
	joro@...tes.org, will@...nel.org, robin.murphy@....com,
	shuah@...nel.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, eric.auger@...hat.com,
	baolu.lu@...ux.intel.com, yi.l.liu@...el.com, yury.norov@...il.com,
	jacob.pan@...ux.microsoft.com, patches@...ts.linux.dev
Subject: Re: [PATCH v2 7/7] iommu: Turn iova_cookie to dma-iommu private
 pointer

On Wed, Feb 26, 2025 at 10:57:00AM -0800, Nicolin Chen wrote:
> OK, I see. But we are also changing the behavior for the
> !CONFIG_IOMMU_DMA configuration, in which case all other iommu
> functions seem to return -ENODEV. And I assume we would need a
> justification for such a change?
> 
> Perhaps, this can be explicit, just to keep the consistency:
> 	/* NOP if IOMMU driver reports SW_MSI reserved regions */
> 	return IS_ENABLED(CONFIG_IOMMU_DMA) ? 0 : -ENODEV;

Hurm, I donno, if we don't have a IRQ driver that supports it then it
doesn't matter that IOMMU_DMA is off either because there is nothing
that would call into IOMMU_DMA in the first place.

Success still seems like the right answer on such a weirdo kconfig.

Jason