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Date:   Thu, 7 Jan 2021 16:19:37 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To:     Florian Fainelli <f.fainelli@gmail.com>
Cc:     Claire Chang <tientzu@chromium.org>,
        Rob Herring <robh+dt@kernel.org>, mpe@ellerman.id.au,
        benh@kernel.crashing.org, paulus@samba.org,
        "list@263.net:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>,
        Joerg Roedel <joro@8bytes.org>, will@kernel.org,
        Frank Rowand <frowand.list@gmail.com>,
        boris.ostrovsky@oracle.com, jgross@suse.com,
        sstabellini@kernel.org, Christoph Hellwig <hch@lst.de>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>, grant.likely@arm.com,
        xypron.glpk@gmx.de, Thierry Reding <treding@nvidia.com>,
        mingo@kernel.org, bauerman@linux.ibm.com, peterz@infradead.org,
        Greg KH <gregkh@linuxfoundation.org>,
        Saravana Kannan <saravanak@google.com>,
        rafael.j.wysocki@intel.com, heikki.krogerus@linux.intel.com,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        rdunlap@infradead.org, dan.j.williams@intel.com,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        linux-devicetree <devicetree@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        linuxppc-dev@lists.ozlabs.org, xen-devel@lists.xenproject.org,
        Tomasz Figa <tfiga@chromium.org>,
        Nicolas Boichat <drinkcat@chromium.org>
Subject: Re: [RFC PATCH v3 2/6] swiotlb: Add restricted DMA pool
Message-ID: <20210107211937.GA19460@char.us.oracle.com>
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On Thu, Jan 07, 2021 at 10:09:14AM -0800, Florian Fainelli wrote:
> On 1/7/21 9:57 AM, Konrad Rzeszutek Wilk wrote:
> > On Fri, Jan 08, 2021 at 01:39:18AM +0800, Claire Chang wrote:
> >> Hi Greg and Konrad,
> >>
> >> This change is intended to be non-arch specific. Any arch that lacks DMA access
> >> control and has devices not behind an IOMMU can make use of it. Could you share
> >> why you think this should be arch specific?
> > 
> > The idea behind non-arch specific code is it to be generic. The devicetree
> > is specific to PowerPC, Sparc, and ARM, and not to x86 - hence it should
> > be in arch specific code.
> 
> In premise the same code could be used with an ACPI enabled system with
> an appropriate service to identify the restricted DMA regions and unlock
> them.

Which this patchset is not.

> 
> More than 1 architecture requiring this function (ARM and ARM64 are the
> two I can think of needing this immediately) sort of calls for making
> the code architecture agnostic since past 2, you need something that scales.

I believe the use-case is for ARM64 at this moment.

> 
> There is already code today under kernel/dma/contiguous.c that is only
> activated on a CONFIG_OF=y && CONFIG_OF_RESERVED_MEM=y system, this is
> no different.
> -- 
> Florian