[RFC 1/5] dt-bindings: iommu: Add reserved-dma-region for IOMMU device

[Jitendra Bhivare]

On Tue, Mar 6, 2018 at 5:11 PM, Robin Murphy <robin.murphy at arm.com> wrote:
>
> On 06/03/18 04:59, Jitendra Bhivare wrote:
>>
>> Certain regions in IO virtual address space may need to be reserved to be
>> not used for devices configured behind IOMMU.
>>
>> Add documentation of the property to allow such regions to be specified in
>> DT to be reserved using IOMMU_RESV_RESERVED type.
>
>
> That sounds like software policy; DT is for describing hardware.
It is to describe the holes in address space for which hardware can't
provide mappings.
>
>> Reviewed-by: Ray Jui <ray.jui at broadcom.com>
>> Reviewed-by: Vikram Prakash <vikram.prakash at broadcom.com>
>> Reviewed-by: Scott Branden <scott.branden at broadcom.com>
>> Signed-off-by: Jitendra Bhivare <jitendra.bhivare at broadcom.com>
>> ---
>>   Documentation/devicetree/bindings/iommu/iommu.txt | 17 +++++++++++++++++
>>   1 file changed, 17 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/iommu/iommu.txt b/Documentation/devicetree/bindings/iommu/iommu.txt
>> index 5a8b462..5a58ef2 100644
>> --- a/Documentation/devicetree/bindings/iommu/iommu.txt
>> +++ b/Documentation/devicetree/bindings/iommu/iommu.txt
>> @@ -98,6 +98,20 @@ requirements of that use-case haven't been fully determined yet. Implementing
>>   this is therefore not recommended without further discussion and extension of
>>   this binding.
>>   +Optional properties:
>> +--------------------
>> +- reserved-dma-region: This specifies DMA region to be reserved with specific
>> +  prot in IOVA space. It is in tuples of (busno,prot,bus_addr,size).
>
>
> What do busno and prot actually mean, and what are valid values for them?
>
> Robin.
busno was part of initial commit 4e0ee78f in implementation of
of_get_dma_window.
I am not sure what was the use of it in PowerPC. Similar
implementation can be seen
in of_parse_dma_window.
prot is access permission flags for the region for reserving in SW.
This I will remove.
>
>
>> +- #region-address-cells: specifies number of cells needed to encode bus_addr
>> +
>> +- #region-size-cells: specifies number of cells needed to encode size
>> +
>> +Notes:
>> +======
>> +This can be applied to IOMMU master node or to children (such as PCI host
>> +bridges) on the bus behind IOMMU.
>> +
>>     Examples:
>>   =========
>> @@ -173,6 +187,9 @@ Multiple-master IOMMU with configurable DMA window:
>>                          * master (i.e. the I/O virtual address space).
>>                          */
>>                         #iommu-cells = <4>;
>> +                       #region-address-cells = <2>;
>> +                       #region-size-cells = <2>;
>> +                       reserved-dma-region = <0x0 0x0 0x04 0x0 0x04 0x0>;
>>                 };
>>                 master {
>>