Re: [PATCH v7 14/15] dt-bindings: of: Add restricted DMA pool

Claire Chang
2021-05-27T11:29:51Z

On Wed, May 26, 2021 at 11:53 PM Will Deacon <will@kernel.org> wrote:
>
> On Wed, May 26, 2021 at 01:13:22PM +0100, Will Deacon wrote:
> > On Tue, May 18, 2021 at 02:42:14PM +0800, Claire Chang wrote:
> > > @@ -138,4 +160,9 @@ one for multimedia processing (named multimedia-memory@77000000, 64MiB).
> > > memory-region = <&multimedia_reserved>;
> > > /* ... */
> > > };
> > > +
> > > + pcie_device: pcie_device@0,0 {
> > > + memory-region = <&restricted_dma_mem_reserved>;
> > > + /* ... */
> > > + };
> >
> > I still don't understand how this works for individual PCIe devices -- how
> > is dev->of_node set to point at the node you have above?
> >
> > I tried adding the memory-region to the host controller instead, and then
> > I see it crop up in dmesg:
> >
> > | pci-host-generic 40000000.pci: assigned reserved memory node restricted_dma_mem_reserved
> >
> > but none of the actual PCI devices end up with 'dma_io_tlb_mem' set, and
> > so the restricted DMA area is not used. In fact, swiotlb isn't used at all.
> >
> > What am I missing to make this work with PCIe devices?
>
> Aha, looks like we're just missing the logic to inherit the DMA
> configuration. The diff below gets things working for me.

I guess what was missing is the reg property in the pcie_device node.
Will update the example dts.