linux-kernel - Re: [PATCH v9 3/7] iommu: Add verisilicon IOMMU driver

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Message-ID: <aMkkYU-p2ouknnAc@willie-the-truck>
Date: Tue, 16 Sep 2025 09:48:33 +0100
From: Will Deacon <will@...nel.org>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: Jörg Rödel <joro@...tes.org>,
	Nicolas Dufresne <nicolas.dufresne@...labora.com>,
	Benjamin Gaignard <benjamin.gaignard@...labora.com>,
	robin.murphy@....com, robh@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, heiko@...ech.de, p.zabel@...gutronix.de,
	mchehab@...nel.org, iommu@...ts.linux.dev,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, kernel@...labora.com,
	linux-media@...r.kernel.org
Subject: Re: [PATCH v9 3/7] iommu: Add verisilicon IOMMU driver

On Mon, Sep 15, 2025 at 07:58:06PM -0300, Jason Gunthorpe wrote:
> On Sat, Sep 13, 2025 at 07:58:04AM +0200, Jörg Rödel wrote:
> > [Adding Will back to Cc]
> > 
> > On Fri, Sep 12, 2025 at 01:37:11PM -0400, Nicolas Dufresne wrote:
> > > To me this rejection isn't about Benjamin's driver, all iommu seems to look
> > > alike, so anyone else that would have sent new driver would have face the same
> > > issue.
> > 
> > This is about ignoring comments from one of the IOMMU maintainers. I am not
> > going to merge a driver with open comments/objections[1] from Will (and a few
> > others), so resolve this with him and get his Ack.
> 
> I would strongly object to trying to share map_pages, unmap_pages,
> iova_to_phys, free and other iommu pt related functions in some
> limited way instead of helping on the much more complete iommu pt
> work. Which is what I said to Will, but for some reason he suggested
> it anyhow.

If the answer is to convert this to iommu pt, then so be it. My
understanding was that was still premature at this stage but you know
better than me.

When I bothered to look at this driver side-by-side with the rockchip
driver which, despite apparently being totally different IP (honest!),
is *remarkably* similar, I summarised the similarity in the default
domain ops:

https://lore.kernel.org/all/aH5yR9CkYSJ4PaZV@willie-the-truck/

But rather than respond to that, Benjamin just sent a new version. I
was hoping for a bit more discussion...

> Sorry, but it doesn't make sense to complain about duplication in
> drivers and then not help advance one of the biggest projects to
> actually concretely and comprehensively address that duplication.

I don't think it needs to be one or the other. afaict, these drivers
should share the default domain ops and if the page-table code is using
iommu-pt then that's even better.

Will