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

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

[Chen-Yu Tsai]

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

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

[Bjorn Helgaas]

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@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?

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.

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

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

Re: [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@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@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
> >

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

[AngeloGioacchino Del Regno]

On 5/8/26 08:36, 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@chromium.org>

Makes a lot of sense, and actually makes us able to provide a correct hardware
description in the devicetrees.

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>