linux-kernel - Re: [PATCH 7/7] dma-mapping: Simplify arch_setup_dma

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Date:   Mon, 4 Dec 2023 12:54:53 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     Joerg Roedel <joro@...tes.org>, 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>,
        Jason Gunthorpe <jgg@...pe.ca>, 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 7/7] dma-mapping: Simplify arch_setup_dma_ops()

On 04/12/2023 8:44 am, Christoph Hellwig wrote:
> On Wed, Nov 29, 2023 at 05:43:04PM +0000, Robin Murphy wrote:
>> The dma_base, size and iommu arguments are only used by ARM, and can
>> now easily be deduced from the device itself, so there's no need to pass
>> them through the callchain as well.
> 
> This looks even better than the patch form Jason that only removed the
> iommu argument:
> 
> Reviewed-by: Christoph Hellwig <hch@....de>
> 
> I wonder if it makes sense to also remove the coherent argument
> by setting up dev->dma_coherent in the caller.  That would require
> a pretty careful audit as we're doing a few weird things in that
> area, though.

Yeah, it crossed my mind too, but then I remembered we have at least the 
ARM stuff which may have already set a platform-specific value for 
dev->dma_coherent to take precedence over the firmware value, thus still 
needs to differentiate between the two at this point. Leaving the 
established argument in place seems neater IMO than having to go back to 
arch-specific mechanisms for that and any other similar tricks.

Thanks,
Robin.