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SubjectRe: [RFC PATCH 1/2] dt-bindings: pci: Add drop mask property for MSI and IOMMU
On Fri, Jul 07, 2017 at 12:39:58PM +0530, Srinath Mannam wrote:
> This patch adds info about optional DT properties
> iommu-map-drop-mask and msi-map-drop-mask.
>
> A drop mask represents the bits which will be
> removed/dropped by system from Requester ID before
> mapping it to msi ID or stream ID.
>
> Signed-off-by: Anup Patel <anup.patel@broadcom.com>
> Signed-off-by: Oza Pawandeep <oza.oza@broadcom.com>
> Signed-off-by: Srinath Mannam <srinath.mannam@broadcom.com>
> Reviewed-by: Ray Jui <ray.jui@broadcom.com>
> Reviewed-by: Scott Branden <scott.branden@broadcom.com>
> ---
> .../devicetree/bindings/pci/pci-iommu.txt | 31 ++++++++++++++++++++
> Documentation/devicetree/bindings/pci/pci-msi.txt | 33 ++++++++++++++++++++++
> 2 files changed, 64 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/pci/pci-iommu.txt b/Documentation/devicetree/bindings/pci/pci-iommu.txt
> index 0def586..499cb27 100644
> --- a/Documentation/devicetree/bindings/pci/pci-iommu.txt
> +++ b/Documentation/devicetree/bindings/pci/pci-iommu.txt
> @@ -44,6 +44,9 @@ Optional properties
> - iommu-map-mask: A mask to be applied to each Requester ID prior to being
> mapped to an IOMMU specifier per the iommu-map property.
>
> +- iommu-map-drop-mask: A drop mask represents the bits which will be
> + removed/dropped by system from Requester ID before mapping it to
> + stream ID.

As mentioned in my reply to the cover letter, you're expecting this to
be handled as more than a mask, so this description is inadequate.

[...]

> +/ {
> + #address-cells = <1>;
> + #size-cells = <1>;
> +
> + iommu: iommu@a {
> + reg = <0xa 0x1>;
> + compatible = "vendor,some-iommu";
> + #iommu-cells = <1>;
> + };
> +
> + pci: pci@f {
> + reg = <0xf 0x1>;
> + compatible = "vendor,pcie-root-complex";
> + device_type = "pci";
> +
> + /*
> + * The sideband data provided to the IOMMU is a 10bit
> + * data derived from the RID by dropping 4 MSBs
> + * of device number and 2 MSBs of function number.
> + */
> + iommu-map = <0x0 &iommu 0x0 0x1024>;
> + iommu-map-drop-mask = <0xff09>;
> + };
> +};

... as this this example.

Assuming this was truly a mask of bits to drop, you'd have:

RID -> SID
0xffff -> 0x00f6

... whereas from your cover letter it seems you want:

RID -> SID
0xffff -> 0x3f

... and I've just realsied you have non-coniguous masks, so this is even
worse.

> diff --git a/Documentation/devicetree/bindings/pci/pci-msi.txt b/Documentation/devicetree/bindings/pci/pci-msi.txt
> index 9b3cc81..1de3f39 100644
> --- a/Documentation/devicetree/bindings/pci/pci-msi.txt
> +++ b/Documentation/devicetree/bindings/pci/pci-msi.txt
> @@ -49,6 +49,10 @@ Optional properties
> - msi-map-mask: A mask to be applied to each Requester ID prior to being mapped
> to an msi-specifier per the msi-map property.
>
> +- msi-map-drop-mask: A drop mask represents the bits which will be
> + removed/dropped by system from Requester ID before mapping it to
> + msi ID.
> +
> - msi-parent: Describes the MSI parent of the root complex itself. Where
> the root complex and MSI controller do not pass sideband data with MSI
> writes, this property may be used to describe the MSI controller(s)
> @@ -218,3 +222,32 @@ Example (5)
> <0x0000 &msi_b 0x0000 0x10000>;
> };
> };
> +
> +Example (6)
> +===========
> +
> +/ {
> + #address-cells = <1>;
> + #size-cells = <1>;
> +
> + msi: msi-controller@a {
> + reg = <0xa 0x1>;
> + compatible = "vendor,some-controller";
> + msi-controller;
> + #msi-cells = <1>;
> + };
> +
> + pci: pci@f {
> + reg = <0xf 0x1>;
> + compatible = "vendor,pcie-root-complex";
> + device_type = "pci";
> +
> + /*
> + * The sideband data provided to the MSI controller is
> + * a 10bit data derived from the RID by dropping
> + * 4 MSBs of device number and 2 MSBs of function number.
> + */
> + msi-map = <0x0 &msi_a 0x0 0x100>,
> + msi-map-drop-mask = <0xff09>
> + };
> +};

... likewise on all counts.

Your mapping can be expressed today using a number of msi-map entries,
which you can easily generate programmatically with a trivial perl
script, without requiring a new binding or any new kernel code.

Please do that instead.
Thanks,
Mark.

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