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

From: Benjamin Gaignard <benjamin.gaignard@collabora.com>
To: Will Deacon <will@kernel.org>, Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Jörg Rödel" <joro@8bytes.org>,
	"Nicolas Dufresne" <nicolas.dufresne@collabora.com>,
	robin.murphy@arm.com, robh@kernel.org, krzk+dt@kernel.org,
	conor+dt@kernel.org, heiko@sntech.de, p.zabel@pengutronix.de,
	mchehab@kernel.org, iommu@lists.linux.dev,
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-rockchip@lists.infradead.org, kernel@collabora.com,
	linux-media@vger.kernel.org
Subject: Re: [PATCH v9 3/7] iommu: Add verisilicon IOMMU driver
Date: Tue, 16 Sep 2025 11:30:20 +0200	[thread overview]
Message-ID: <0eff8b1a-c45f-47b1-a871-59f4a0101f0f@collabora.com> (raw)
In-Reply-To: <aMkkYU-p2ouknnAc@willie-the-truck>

Le 16/09/2025 à 10:48, Will Deacon a écrit :
> 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 if that had offend, you it wasn't the purpose.

Where you see similarities in the pattern I see lot of differences
everywhere that will required to duplicate the functions for each
hardware (locking schema, bit definition, power management, enable/disable).

Since the v6 I have fix lot of locking and pm_runtime issue and add a
function, needed by the video decoder, to flush the TLB.

My first attempt when writing Verisilicon driver was to add a variant
(like for rk iommu v2 I had already done) to Rockchip driver but mixing or
sharing structures or functions between Rockchip and Verisilicon is just a
nightmare because it requires to add "if else" everywhere.

Benjamin

>
>> 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

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