Re: [PATCH] iommu/dma: Explicitly sort PCI DMA windows

[dann frazier <dann.frazier@canonical.com>]

On Wed, Mar 23, 2022 at 09:49:04AM +0000, Marc Zyngier wrote:
> On Tue, 22 Mar 2022 17:27:36 +0000,
> Robin Murphy <robin.murphy@arm.com> wrote:
> > 
> > Originally, creating the dma_ranges resource list in pre-sorted fashion
> > was the simplest and most efficient way to enforce the order required by
> > iova_reserve_pci_windows(). However since then at least one PCI host
> > driver is now re-sorting the list for its own probe-time processing,
> > which doesn't seem entirely unreasonable, so that basic assumption no
> > longer holds. Make iommu-dma robust and get the sort order it needs by
> > explicitly sorting, which means we can also save the effort at creation
> > time and just build the list in whatever natural order the DT had.
> > 
> > Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> > ---
> > 
> > Looking at this area off the back of the XGene thread[1] made me realise
> > that we need to do it anyway, regardless of whether it might also happen
> > to restore the previous XGene behaviour or not. Presumably nobody's
> > tried to use pcie-cadence-host behind an IOMMU yet...
> 
> This definitely restores PCIe functionality on my Mustang (XGene-1).
> Hopefully dann can comment on whether this addresses his own issue, as
> his firmware is significantly different.

Robin, Marc,

Adding just this patch on top of v5.17 (w/ vendor dtb) isn't enough to
fix m400 networking:

  https://paste.ubuntu.com/p/H5ZNbRvP8V/

  -dann