Re: [RFC PATCH 1/2] dt-bindings: pci: Add drop mask property for MSI and IOMMU

[Mark Rutland <mark.rutland@arm.com>]

On Fri, Jul 07, 2017 at 08:22:21AM -0700, Scott Branden wrote:
> On 17-07-07 07:55 AM, Robin Murphy wrote:
> >On 07/07/17 14:30, Mark Rutland wrote:
> >>On Fri, Jul 07, 2017 at 12:39:58PM +0530, Srinath Mannam wrote:
> >>>+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.
> >
> >Indeed. The systems I'm aware of which need to express non-trivial RID
> >to SID mappings tend to have the bootloader probe PCI and dynamically
> >generate map entries per discovered RID, but even if you wanted to
> >statically generate the whole lot for the worst-case bus range that's
> >still only 512 entries, which is not unmanageable. Notably, it's also
> >what would have to be done (in equivalent) for IORT, although I assume
> >this is an embedded platform for which nobody cares about ACPI.
>
> Actually we will care about ACPI and need to add it (doesn't need to
> be in this patchet unless easy to do so...)

Similarly to what I said for the DT case, with IORT you can solve this
today by using multiple ID mapping entries in a node's ID mappings
array.

I don't imagine the sort of change you are proposing will sail into the
IORT spec.

Thanks,
Mark.