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From: Mark Rutland <mark.rutland@arm.com>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Laszlo Ersek <lersek@redhat.com>,
	"kvmarm@lists.cs.columbia.edu" <kvmarm@lists.cs.columbia.edu>
Subject: Re: issues with emulated PCI MMIO backed by host memory under KVM
Date: Mon, 27 Jun 2016 14:49:10 +0100	[thread overview]
Message-ID: <20160627134910.GH1113@leverpostej> (raw)
In-Reply-To: <CAFEAcA93LRGxajFPBVo+wju74QApRWDN8MSKuvtaybwruFgH_w@mail.gmail.com>

On Mon, Jun 27, 2016 at 02:15:29PM +0100, Peter Maydell wrote:
> On 27 June 2016 at 10:47, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> > As for the USB case, I can't really figure out what is going on here,
> > but I am fairly certain it is a different issue. If this is related to
> > DMA, I wonder if adding the 'dma-coherent' property to the PCIe root
> > complex node fixes anything.
> 
> I get the impression dma-coherent is the right thing to advertise
> anyway. Do you have the documentation to hand that specifies what
> "dma-coherent" means? The Documentation/devicetree docs in the
> kernel tree seem to rather unhelpfully define it as "Present if
> dma operations are coherent", which doesn't really clarify anything
> to me...

It's ill-defined today, and the precise definition is an open question.
See replies to [1], which seems to have stalled as of [2].

My view is that for arm/arm64 this should mean the device makes accesses
which are coherent with Inner Shareable Normal Inner-WB Outer-WB
attributes, as this is the functional de-facto semantics today, and
anything short of that is not well-defined or usable.

Thanks,
Mark.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-June/433626.html
[2] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-June/434143.html

  reply	other threads:[~2016-06-27 13:44 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-24 14:04 issues with emulated PCI MMIO backed by host memory under KVM Ard Biesheuvel
2016-06-24 14:57 ` Andrew Jones
2016-06-27  8:17   ` Marc Zyngier
2016-06-24 18:16 ` Ard Biesheuvel
2016-06-25  7:15   ` Alexander Graf
2016-06-25  7:19 ` Alexander Graf
2016-06-27  8:11   ` Marc Zyngier
2016-06-27  9:16 ` Christoffer Dall
2016-06-27  9:47   ` Ard Biesheuvel
2016-06-27 10:34     ` Christoffer Dall
2016-06-27 12:30       ` Ard Biesheuvel
2016-06-27 13:35         ` Christoffer Dall
2016-06-27 13:57           ` Ard Biesheuvel
2016-06-27 14:29             ` Alexander Graf
2016-06-28 11:02               ` Laszlo Ersek
2016-06-28 10:04             ` Christoffer Dall
2016-06-28 11:06               ` Laszlo Ersek
2016-06-28 12:20                 ` Christoffer Dall
2016-06-28 13:10                   ` Catalin Marinas
2016-06-28 13:19                     ` Ard Biesheuvel
2016-06-28 13:25                       ` Catalin Marinas
2016-06-28 14:02                         ` Andrew Jones
2016-06-27 14:24       ` Alexander Graf
2016-06-28 10:55       ` Laszlo Ersek
2016-06-28 13:14         ` Ard Biesheuvel
2016-06-28 13:32           ` Laszlo Ersek
2016-06-29  7:12             ` Gerd Hoffmann
2016-06-28 15:23         ` Alexander Graf
2016-06-27 13:15     ` Peter Maydell
2016-06-27 13:49       ` Mark Rutland [this message]
2016-06-27 14:10         ` Peter Maydell
2016-06-28 10:05           ` Christoffer Dall

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