linux-kernel - Re: [PATCH 1/4] of/fdt: Update zone_dma

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Message-ID: <20201012064715.GA2548@lst.de>
Date:   Mon, 12 Oct 2020 08:47:15 +0200
From:   Christoph Hellwig <hch@....de>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        iommu@...ts.linux-foundation.org, Rob Herring <robh+dt@...nel.org>,
        linux-rpi-kernel@...ts.infradead.org,
        Frank Rowand <frowand.list@...il.com>,
        Christoph Hellwig <hch@....de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 1/4] of/fdt: Update zone_dma_bits when running in
 bcm2711

On Fri, Oct 09, 2020 at 06:10:52PM +0100, Catalin Marinas wrote:
> kdump wants DMA-able memory and,

DMAable by whom?  The only way to guranteed DMAable memory is to use
the DMA memory allocator(s) and pass a specific device to them.  Everyting
else is just fundamentally broken.  Note that even when device is not
DMAable we can still use swiotlb to access it.