linux-kernel - Re: [PATCH v2] dma-mapping: treat dev->bus_dma

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Message-ID: <0b851d0e-37c7-062e-c287-05f8c8a54c16@arm.com>
Date:   Mon, 25 Nov 2019 16:33:17 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>,
        Nathan Chancellor <natechancellor@...il.com>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Hanjun Guo <guohanjun@...wei.com>,
        Sudeep Holla <sudeep.holla@....com>,
        Jens Axboe <axboe@...nel.dk>, Joerg Roedel <joro@...tes.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-ide@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paul Burton <paulburton@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>, x86@...nel.org,
        linux-acpi@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        James Hogan <jhogan@...nel.org>, Len Brown <lenb@...nel.org>,
        devicetree@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        linux-mips@...r.kernel.org, Ralf Baechle <ralf@...ux-mips.org>,
        iommu@...ts.linux-foundation.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] dma-mapping: treat dev->bus_dma_mask as a DMA limit

On 25/11/2019 7:44 am, Christoph Hellwig wrote:
> On Sat, Nov 23, 2019 at 09:51:08AM -0700, Nathan Chancellor wrote:
>> Just as an FYI, this introduces a warning on arm32 allyesconfig for me:
> 
> I think the dma_limit argument to iommu_dma_alloc_iova should be a u64
> and/or we need to use min_t and open code the zero exception.
> 
> Robin, Nicolas - any opinions?

Yeah, given that it's always held a mask I'm not entirely sure why it 
was ever a dma_addr_t rather than a u64. Unless anyone else is desperate 
to do it I'll get a cleanup patch ready for rc1.

> Also I wonder how this file gets compiled on arm32 given that arm32
> has its own set of iommu dma ops..

As long as the dependencies for CONFIG_IOMMU_DMA are met it can be built 
even when it's not actually used. That said, I might have expected that 
arm allyesconfig ends up with CONFIG_ARCH_DMA_ADDR_T_64BIT=y anyway; I 
guess it must pick some of CONFIG_ARM_LPAE's negative dependencies.

(/me doesn't feel like jumping down the all*config rabbit hole today)

Robin.