[PATCH] dt-bindings: PCI: mediatek-gen3: Allow memory-region for restricted DMA buffer

[Chen-Yu Tsai]

On Sat, May 9, 2026 at 1:54 AM Bjorn Helgaas <helgaas at kernel.org> wrote:
>
> On Fri, May 08, 2026 at 02:36:32PM +0800, Chen-Yu Tsai wrote:
> > On some SoCs without an IOMMU behind the PCIe controller, the PCIe
> > controller memory access could be limited to a small region by the
> > firmware configuring a memory protection unit. This memory region
> > must be assigned to the PCIe controller so that the OS knows to
> > use that region. Otherwise PCIe devices would not work properly.
> >
> > Allow the memory-region property with one item pointing to a
> > restricted DMA buffer.
> >
> > Signed-off-by: Chen-Yu Tsai <wenst at chromium.org>
> > ---
> > This patch compliments another patch that moved the memory-region from
> > the PCIe device to the PCIe controller [1].
> >
> > [1] https://lore.kernel.org/all/20260430120725.241779-1-wenst@chromium.org/
> >
> >  Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml b/Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml
> > index 4db700fc36ba..4a9e41d01628 100644
> > --- a/Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml
> > +++ b/Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml
> > @@ -115,6 +115,10 @@ properties:
> >    power-domains:
> >      maxItems: 1
> >
> > +  memory-region:
> > +    maxItems: 1
> > +    description: phandle to restricted DMA buffer
>
> I guess this is similar to
> https://lore.kernel.org/linux-pci/20250716053950.199079-1-huaqian.li@siemens.com/
> and uses
> https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/reserved-memory/shared-dma-pool.yaml?

Correct.

> Looks like those keystone changes were never merged; I don't know what
> happened to them.  But it will be good if everybody does it the same
> way.

Not sure what you mean. "dt-bindings: PCI: ti,am65: Extend for use with
PVU" was merged as commit 57a48a2619c5. Maybe you are referring to the
last patch in that series that adds a DT overlay?

> I wish there were a simple way to grep for this restricted DMA
> concept.  Maybe there is and I just haven't found it :)

Probably just grepping for "restricted" in the PCI bindings. :|


ChenYu

> >    mediatek,pbus-csr:
> >      $ref: /schemas/types.yaml#/definitions/phandle-array
> >      items:
> > --
> > 2.54.0.563.g4f69b47b94-goog
> >