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

[Marc Zyngier <maz@kernel.org>]

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.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.