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: <148a3c8ee53af585b42ec025c2c7821ad852c66c.camel@infradead.org>
Date: Thu, 03 Apr 2025 08:28:19 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: Christoph Hellwig <hch@...radead.org>
Cc: virtio-comment@...ts.linux.dev, mst@...hat.com, 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 Thu, 2025-04-03 at 00:24 -0700, Christoph Hellwig wrote:
> 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.

Linux has 'SWIOTLB' support, but I didn't see it as a term specific to
that particular implementation; it seemed like a concept would would be
understood elsewhere. But sure, I'm happy to rename it to just 'bounce
buffers' or something like that. I'll see what I can come up with that
is succinct enough to use in VIRTIO_F_xxx and VIRTIO_PCI_CAP_xxx names.

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