Re: [PATCH v8 6/6] coco: guest: arm64: Replace dummy CCA device with sysfs ABI

[Suzuki K Poulose]

On 07/07/2026 09:13, Aneesh Kumar K.V (Arm) wrote:
> The SMCCC firmware driver now creates the arm-smccc platform device and
> instantiates the CCA RSI auxiliary devices once the RSI ABI is discovered.
> The arm64-specific arm-cca-dev platform device stub is therefore no longer
> needed.
>
> However, userspace has used the arm-cca-dev platform device to detect Arm
> CCA Realm guests [1]. Removing it without a replacement would break that
> detection and would also leave userspace depending on kernel device-model
> details.
>
> Add /sys/firmware/cca/realm_guest as a stable, architecture-provided ABI
> for detecting whether the kernel is running as an Arm CCA Realm guest. The
> file returns 1 in Realm world and 0 otherwise, similar to the existing s390
> /sys/firmware/uv/prot_virt_guest interface for protected virtualization
> guests.
>
> Remove the dummy arm-cca-dev registration now that userspace has a
> dedicated CCA Realm guest indicator, and document the new ABI in
> Documentation/ABI/testing/sysfs-firmware-cca.
>
> [1] https://lore.kernel.org/all/4a7d84b2-2ec4-4773-a2d5-7b63d5c683cf@xxxxxxx
>
> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@xxxxxxxxxx>

Acked-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>