Re: [PATCH v3 2/3] iommu/of: fix device tree configuration for PCI devices

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Aug 14, 2025 at 07:32:36PM -0700, Shyam Saini wrote:
> On Thu, Aug 14, 2025 at 09:39:58PM -0300, Jason Gunthorpe wrote:
> > On Thu, Aug 14, 2025 at 04:30:18PM -0700, Shyam Saini wrote:
> > > or were you referring to [2]?
> > > 
> > > In that case, the PCI child node data needs to be parsed, which is
> > > currently handled individually by each host controller driver.
> > 
> > Yes, this looks like it may be what I was thinking of, the pci@1,0
> > specifes the BDF effectively
> 
> In that case, we'll need to parse the child DTS nodes properly
> within of_iommu_get_resv_regions(). I'll include this in v4.

Kinda surprised this isn't happening already? It would be good to
refer to the original specs and describe how whatetever you propose is
aligned there.

> > Presumably this is a fixed issue of the platform. You never did
> > explain how your system has such werdio behavior, or how something
> > like iommu=pt can function on it...
> Yes, this issue is platform-specific. On this platform, the default MSI IOVA
> range overlaps with an address region that is reserved for another purpose,
> Other than that we haven't observed any obvious issues for DMA operations

Usually DRAM is at the default MSI IOVA address, so if you run
iommu=pt then presumably your DRAM map has a nice hole in it.. But
maybe the memory map told the OS about that.

Jason