linux-kernel - Re: [PATCH 0/7] dma-mapping: Clean up arch_setup_dma

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Date:   Wed, 29 Nov 2023 16:36:42 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Joerg Roedel <joro@...tes.org>, Christoph Hellwig <hch@....de>,
        Vineet Gupta <vgupta@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Hanjun Guo <guohanjun@...wei.com>,
        Sudeep Holla <sudeep.holla@....com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-acpi@...r.kernel.org, iommu@...ts.linux.dev,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 0/7] dma-mapping: Clean up arch_setup_dma_ops()

On Wed, Nov 29, 2023 at 05:42:57PM +0000, Robin Murphy wrote:
> Hi all,
> 
> Prompted by Jason's proposal[1], here's a first step towards truly
> unpicking the dma_configure vs. IOMMU mess. As I commented before, we
> have an awful lot of accumulated cruft and technical debt here making
> things more complicated than they need to be, and we already have hacks
> on top of hacks trying to work around it, so polishing those hacks even
> further is really not a desirable direction of travel. And I do know
> they're hacks, because I wrote most of them and still remember enough of
> the context of the time ;)

I quite like this, I was also looking at getting rid of those other
parameters.

I wanted to take smaller steps because it is all pretty hairy.

One thing that still concerns me is if the FW data restricts the valid
IOVA window that really should be reflected into the reserved ranges
and not just dumped into the struct device for use by the DMA API.

Or, perhaps, viof/iommufd should be using the struct device data to
generate some additional reserved ranges?

Either way, I would like to see the dma_iommu and the rest of the
subsystem agree on what the valid IOVA ranges actually are.

Jason