* Re: [PATCH v2 2/2] virtio: Document DMA coherency
[not found] ` <6cc1be2a3ace621293157a9828c9f1d3f47147c8.1486053223.git.robin.murphy@arm.com>
@ 2017-02-03 9:52 ` Will Deacon
2017-02-07 18:45 ` Rob Herring
1 sibling, 0 replies; 3+ messages in thread
From: Will Deacon @ 2017-02-03 9:52 UTC (permalink / raw)
To: Robin Murphy
Cc: mark.rutland, devicetree, pawel.moll, mst, virtualization,
robh+dt, linux-arm-kernel
On Thu, Feb 02, 2017 at 04:36:21PM +0000, Robin Murphy wrote:
> Since making use of the DMA API will require the architecture code to
> have the correct notion of device cache-coherency on architectures like
> ARM, explicitly call this out in the virtio-mmio DT binding. The ship
> has sailed for legacy virtio, but let's hope that we can head off any
> future firmware mishaps.
>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
> Documentation/devicetree/bindings/virtio/mmio.txt | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/virtio/mmio.txt b/Documentation/devicetree/bindings/virtio/mmio.txt
> index 5069c1b8e193..999a93faa67c 100644
> --- a/Documentation/devicetree/bindings/virtio/mmio.txt
> +++ b/Documentation/devicetree/bindings/virtio/mmio.txt
> @@ -7,6 +7,16 @@ Required properties:
> - compatible: "virtio,mmio" compatibility string
> - reg: control registers base address and size including configuration space
> - interrupts: interrupt generated by the device
> +- dma-coherent: required if the device (or host emulation) accesses memory
> + cache-coherently, absent otherwise
> +
> +Linux implementation note:
> +
> +virtio devices not advertising the VIRTIO_F_IOMMU_PLATFORM flag have been
> +implicitly assumed to be cache-coherent by Linux, and for legacy reasons this
> +behaviour is likely to remain. If VIRTIO_F_IOMMU_PLATFORM is advertised, then
> +such assumptions cannot be relied upon and the "dma-coherent" property must
> +accurately reflect the coherency of the device.
>
> Example:
>
> @@ -14,4 +24,5 @@ Example:
> compatible = "virtio,mmio";
> reg = <0x3000 0x100>;
> interrupts = <41>;
> + dma-coherent;
I think this is a sensible update to the binding and is independent of
whatever we decide to do for IOMMUs and DMA on legacy devices.
Acked-by: Will Deacon <will.deacon@arm.com>
Will
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH v2 2/2] virtio: Document DMA coherency
[not found] ` <6cc1be2a3ace621293157a9828c9f1d3f47147c8.1486053223.git.robin.murphy@arm.com>
2017-02-03 9:52 ` Will Deacon
@ 2017-02-07 18:45 ` Rob Herring
1 sibling, 0 replies; 3+ messages in thread
From: Rob Herring @ 2017-02-07 18:45 UTC (permalink / raw)
To: Robin Murphy
Cc: mark.rutland, devicetree, pawel.moll, mst, will.deacon,
virtualization, linux-arm-kernel
On Thu, Feb 02, 2017 at 04:36:21PM +0000, Robin Murphy wrote:
> Since making use of the DMA API will require the architecture code to
> have the correct notion of device cache-coherency on architectures like
> ARM, explicitly call this out in the virtio-mmio DT binding. The ship
> has sailed for legacy virtio, but let's hope that we can head off any
> future firmware mishaps.
>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
> Documentation/devicetree/bindings/virtio/mmio.txt | 11 +++++++++++
> 1 file changed, 11 insertions(+)
Acked-by: Rob Herring <robh@kernel.org>
^ permalink raw reply [flat|nested] 3+ messages in thread