linux-kernel - Re: [RFC PATCH 1/3] content: Add VIRTIO_F_SWIOTLB to negotiate use of SWIOTLB bounce buffers

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Message-ID: <Z-43svGzwoUQaYvg@infradead.org>
Date: Thu, 3 Apr 2025 00:24:34 -0700
From: Christoph Hellwig <hch@...radead.org>
To: David Woodhouse <dwmw2@...radead.org>
Cc: virtio-comment@...ts.linux.dev, mst@...hat.com, hch@...radead.org,
	Claire Chang <tientzu@...omium.org>,
	linux-devicetree <devicetree@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Jörg Roedel <joro@...tes.org>,
	iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	graf@...zon.de
Subject: Re: [RFC PATCH 1/3] content: Add VIRTIO_F_SWIOTLB to negotiate use
 of SWIOTLB bounce buffers

On Wed, Apr 02, 2025 at 12:04:45PM +0100, David Woodhouse wrote:
> Define a VIRTIO_F_SWIOTLB feature which allows the device and driver to
> agree on the use of the SWIOTLB, if present. This enables the device to
> refuse to operate further if the driver does not support the SWIOTLB
> requirement expressed in the device-tree.

This makes no sense whatsoever.  Swiotlb is a Linux guest implementation
detail, virtio is a transport protocol.  Mixing them in the same spec
doesn't even compute.  Please describe the actual on the wire semantics
you want, and don't use the term swiotlb.