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

[Hanjun Guo]

Hi Robin,

On 2020/7/2 0:12, Robin Murphy wrote:
> On 2020-06-30 14:04, Hanjun Guo wrote:
>> 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.
> 
> Is that even a valid case though? The principal thing we want to 
> accommodate here is when device B *is* the one accessing memory, either 
> because it is a bridge with device A sat behind it, or because device A 
> is actually just some logical function or subset of physical device B.

Thanks for the clarify, for CCA attributes, child device should be the
same as its parent and that was written in the ACPI spec, so it's better
to make it clear for other properties in the spec as well.

> 
> If the topology is such that device A is a completely independent device 
> with its own path to memory such that it could have different 
> properties, I would expect that it *should* be described in DSDT, and I 
> can't easily think of a good reason why it wouldn't be. I'm also 
> struggling to imagine how it might even have an ID that had to be 
> interpreted in the context of device B if it wasn't one of the cases 
> above :/
> 
> I don't doubt that people could - or maybe even have - come up with crap 
> DSDT bindings that don't represent the hardware sufficiently accurately, 
> but I'm not sure that should be IORT's problem...

As I said in previous email, I'm not against this patch, and seems
have no regressions for platforms that using named component node
such as D05/D06 (I will test it shortly to make sure), but it's better
to update the wording of the spec (even after this patch set is merged).

Thanks
Hanjun