[PATCH v2 01/12] ACPI/IORT: Make iort_match_node_callback walk the ACPI namespace for NC

[Hanjun Guo]

On 2020/6/30 18:24, Lorenzo Pieralisi wrote:
> On Tue, Jun 30, 2020 at 11:06:41AM +0800, Hanjun Guo wrote:
> 
> [...]
> 
>>> For devices that aren't described in the DSDT - IORT translations
>>> are determined by their ACPI parent device. Do you see/Have you
>>> found any issue with this approach ?
>>
>> The spec says "Describes the IO relationships between devices
>> represented in the ACPI namespace.", and in section 3.1.1.3 Named
>> component node, it says:
> 
> PCI devices aren't necessarily described in the ACPI namespace and we
> still use IORT to describe them - through the RC node.
> 
>> "Named component nodes are used to describe devices that are also
>> included in the Differentiated System Description Table (DSDT). See
>> [ACPI]."
>>
>> So from my understanding, the IORT spec for now, can only do ID
>> translations for devices in the DSDT.
> 
> I think you can read this multiple ways but this patch does not
> change this concept. What changes, is applying parent's node IORT
> mapping to child nodes with no associated DSDT nodes, it is the
> same thing we do with PCI and the _DMA method - we could update
> the wording in the specs if that clarifies but I don't think this
> deliberately disregards the specifications.

I agree, but it's better to update the wording of the spec.

> 
>>>> For a platform device, if I use its parent's full path name for
>>>> its named component entry, then it will match, but this will violate
>>>> the IORT spec.
>>>
>>> Can you elaborate on this please I don't get the point you
>>> are making.
>>
>> For example, device A is not described in DSDT so can't represent
>> as a NC node in IORT. Device B can be described in DSDT and it
>> is the parent of device A, so device B can be represented in IORT
>> with memory access properties and node flags with Substream width
>> and Stall supported info.
>>
>> When we trying to translate device A's ID, we reuse all the memory
>> access properties and node flags from its parent (device B), but
>> will it the same?
> 
> I assume so why wouldn't it be ? Why would be describe them in
> a parent-child relationship if that's not how the system looks like
> in HW ?

The point I'm making is that I'm not sure all the memory access and
stall properties are the same for the parent and the device itself.

> 
> Do you have a specific example in mind that we should be aware of ?
> 
>> So the IORT spec don't support this, at least it's pretty vague
>> I think.
> 
> I think that's a matter of wording, it can be updated if it needs be,
> reach out if you see any issue with the current approach please.

If the all the properties for parent and device itself are the same,
I have no strong opinion for this patch, but it's better to update
the wording of the spec as well.

Thanks
Hanjun