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| -rw-r--r-- | Documentation/devicetree/bindings/arm/secure.txt | 70 |
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diff --git a/Documentation/devicetree/bindings/arm/secure.txt b/Documentation/devicetree/bindings/arm/secure.txt new file mode 100644 index 000000000..f27bbff2c --- /dev/null +++ b/Documentation/devicetree/bindings/arm/secure.txt @@ -0,0 +1,70 @@ +* ARM Secure world bindings + +ARM CPUs with TrustZone support have two distinct address spaces, +"Normal" and "Secure". Most devicetree consumers (including the Linux +kernel) are not TrustZone aware and run entirely in either the Normal +world or the Secure world. However some devicetree consumers are +TrustZone aware and need to be able to determine whether devices are +visible only in the Secure address space, only in the Normal address +space, or visible in both. (One example of that situation would be a +virtual machine which boots Secure firmware and wants to tell the +firmware about the layout of the machine via devicetree.) + +The general principle of the naming scheme for Secure world bindings +is that any property that needs a different value in the Secure world +can be supported by prefixing the property name with "secure-". So for +instance "secure-foo" would override "foo". For property names with +a vendor prefix, the Secure variant of "vendor,foo" would be +"vendor,secure-foo". If there is no "secure-" property then the Secure +world value is the same as specified for the Normal world by the +non-prefixed property. However, only the properties listed below may +validly have "secure-" versions; this list will be enlarged on a +case-by-case basis. + +Defining the bindings in this way means that a device tree which has +been annotated to indicate the presence of Secure-only devices can +still be processed unmodified by existing Non-secure software (and in +particular by the kernel). + +Note that it is still valid for bindings intended for purely Secure +world consumers (like kernels that run entirely in Secure) to simply +describe the view of Secure world using the standard bindings. These +secure- bindings only need to be used where both the Secure and Normal +world views need to be described in a single device tree. + +Valid Secure world properties +----------------------------- + +- secure-status : specifies whether the device is present and usable + in the secure world. The combination of this with "status" allows + the various possible combinations of device visibility to be + specified. If "secure-status" is not specified it defaults to the + same value as "status"; if "status" is not specified either then + both default to "okay". This means the following combinations are + possible: + + /* Neither specified: default to visible in both S and NS */ + secure-status = "okay"; /* visible in both */ + status = "okay"; /* visible in both */ + status = "okay"; secure-status = "okay"; /* visible in both */ + secure-status = "disabled"; /* NS-only */ + status = "okay"; secure-status = "disabled"; /* NS-only */ + status = "disabled"; secure-status = "okay"; /* S-only */ + status = "disabled"; /* disabled in both */ + status = "disabled"; secure-status = "disabled"; /* disabled in both */ + +The secure-chosen node +---------------------- + +Similar to the /chosen node which serves as a place for passing data +between firmware and the operating system, the /secure-chosen node may +be used to pass data to the Secure OS. Only the properties defined +below may appear in the /secure-chosen node. + +- stdout-path : specifies the device to be used by the Secure OS for + its console output. The syntax is the same as for /chosen/stdout-path. + If the /secure-chosen node exists but the stdout-path property is not + present, the Secure OS should not perform any console output. If + /secure-chosen does not exist, the Secure OS should use the value of + /chosen/stdout-path instead (that is, use the same device as the + Normal world OS). |