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

From: Robin Murphy
Date: Fri Jul 07 2017 - 11:43:09 EST

On 07/07/17 16:22, Scott Branden wrote:
> Hi Robin,
> On 17-07-07 07:55 AM, Robin Murphy wrote:
>> On 07/07/17 14:30, Mark Rutland wrote:
>>> 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...)

Ah, OK, that's an even stronger argument for not adding anything new
then - DT "iommu-map" is already marginally more expressive than IORT ID
mappings can be, so there doesn't seem to be much justification for
diverging them further.