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

[Shyam Saini]

Hi Jason,

On Fri, Aug 08, 2025 at 09:15:15AM -0300, Jason Gunthorpe wrote:
> On Wed, Aug 06, 2025 at 02:55:38PM -0700, Shyam Saini wrote:
> > Individual PCI devices lack dedicated device tree nodes, but
> 
> This is not the case, you can put PCI devices in the DT as well, there
> is a syntax for it. Why not do that and have the FW populate it on the
> device node itself?

sorry, I missed that, were you referring to [1] CONFIG_PCI_DYNAMIC_OF_NODES
approach?

I tried a PoC with that and got the expected results. However, it requires
hardcoding PCI device IDs using DECLARE_PCI_FIXUP_FINAL?

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.

This might not be a strong argument, but since firmware updates tend
to happen less frequently than OS updates, any addition or modification
to the FDT would require a firmware update. Wouldn't it be more
maintainable to keep this logic in Linux, which is easier to update
and typically updated more often?
  
> You should CC all the device tree maintainers on something like this
> as well.
> 

sure, Cc'd some more folks

[1] https://lwn.net/Articles/939317/
[2] https://elixir.bootlin.com/linux/v6.16/source/arch/arm64/boot/dts/nvidia/tegra186.dtsi#L1340

Thanks,
Shyam