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

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On Thu, Jul 02, 2020 at 04:22:00PM +0800, Hanjun Guo wrote:
> 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).

Have you managed to test this series ?

Thanks,
Lorenzo



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