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From:   Claire Chang <tientzu@chromium.org>
Date:   Thu, 27 May 2021 19:29:20 +0800
Message-ID: <CALiNf2_sVXnb97++yWusB5PWz8Pzfn9bCKZc6z3tY4bx6-nW8w@mail.gmail.com>
Subject: Re: [PATCH v7 14/15] dt-bindings: of: Add restricted DMA pool
To:     Will Deacon <will@kernel.org>
Cc:     Rob Herring <robh+dt@kernel.org>, mpe@ellerman.id.au,
        Joerg Roedel <joro@8bytes.org>,
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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.