Re: [PATCH v3 09/10] dt-bindings: firmware: add arm,ras-cper

Rob Herring
2026-03-26T15:24:40Z

On Wed, Mar 18, 2026 at 08:48:06PM +0000, Ahmed Tiba wrote:
> Describe the DeviceTree node that exposes the Arm firmware-first
> CPER provider and hook the file into MAINTAINERS so the
> binding has an owner.
>
> Signed-off-by: Ahmed Tiba <ahmed.tiba@arm.com>
> ---
> .../devicetree/bindings/firmware/arm,ras-cper.yaml | 71 ++++++++++++++++++++++
> MAINTAINERS | 5 ++
> 2 files changed, 76 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/firmware/arm,ras-cper.yaml b/Documentation/devicetree/bindings/firmware/arm,ras-cper.yaml
> new file mode 100644
> index 000000000000..bd93cfb8d222
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/firmware/arm,ras-cper.yaml
> @@ -0,0 +1,71 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/firmware/arm,ras-cper.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Arm RAS CPER provider
> +
> +maintainers:
> + - Ahmed Tiba <ahmed.tiba@arm.com>
> +
> +description: |
> + Arm Reliability, Availability and Serviceability (RAS) firmware can expose
> + a firmware-first CPER error source directly via DeviceTree. Firmware
> + provides the CPER Generic Error Status block and notifies the OS through
> + an interrupt.
> +
> +properties:
> + compatible:
> + const: arm,ras-cper
> +
> + reg:
> + minItems: 1
> + items:
> + - description:
> + CPER Generic Error Status block exposed by firmware
> + - description:
> + Optional 32- or 64-bit doorbell register used on platforms
> + where firmware needs an explicit "ack" handshake before overwriting
> + the CPER buffer. Firmware watches bit 0 and expects the OS to set it
> + once the current status block has been consumed.
> +
> + interrupts:
> + maxItems: 1
> + description:
> + Interrupt used to signal that a new status record is ready.
> +
> + memory-region:
> + $ref: /schemas/types.yaml#/definitions/phandle

memory-region already has a defined type. You just need to define how
many entries (maxItems: 1).

> + description:
> + Optional phandle to the reserved-memory entry that backs the status
> + buffer so firmware and the OS use the same carved-out region.
> +
> +required:
> + - compatible
> + - reg
> + - interrupts
> +
> +additionalProperties: false
> +
> +examples:
> + - |
> + #include <dt-bindings/interrupt-controller/arm-gic.h>
> +
> + reserved-memory {
> + #address-cells = <2>;
> + #size-cells = <2>;
> + ras_cper_buffer: cper@fe800000 {
> + reg = <0x0 0xfe800000 0x0 0x1000>;
> + no-map;
> + };
> + };
> +
> + error-handler@fe800000 {
> + compatible = "arm,ras-cper";
> + reg = <0xfe800000 0x1000>,

Wait! Why is the reserved address here? There's 2 problems with that.
There shouldn't be same address in 2 places in the DT. The 2nd is
reserved memory should only be regions within DRAM (or whatever is
system memory).

Rob