1* ARM Secure world bindings 2 3ARM CPUs with TrustZone support have two distinct address spaces, 4"Normal" and "Secure". Most devicetree consumers (including the Linux 5kernel) are not TrustZone aware and run entirely in either the Normal 6world or the Secure world. However some devicetree consumers are 7TrustZone aware and need to be able to determine whether devices are 8visible only in the Secure address space, only in the Normal address 9space, or visible in both. (One example of that situation would be a 10virtual machine which boots Secure firmware and wants to tell the 11firmware about the layout of the machine via devicetree.) 12 13The general principle of the naming scheme for Secure world bindings 14is that any property that needs a different value in the Secure world 15can be supported by prefixing the property name with "secure-". So for 16instance "secure-foo" would override "foo". For property names with 17a vendor prefix, the Secure variant of "vendor,foo" would be 18"vendor,secure-foo". If there is no "secure-" property then the Secure 19world value is the same as specified for the Normal world by the 20non-prefixed property. However, only the properties listed below may 21validly have "secure-" versions; this list will be enlarged on a 22case-by-case basis. 23 24Defining the bindings in this way means that a device tree which has 25been annotated to indicate the presence of Secure-only devices can 26still be processed unmodified by existing Non-secure software (and in 27particular by the kernel). 28 29Note that it is still valid for bindings intended for purely Secure 30world consumers (like kernels that run entirely in Secure) to simply 31describe the view of Secure world using the standard bindings. These 32secure- bindings only need to be used where both the Secure and Normal 33world views need to be described in a single device tree. 34 35Valid Secure world properties 36----------------------------- 37 38- secure-status : specifies whether the device is present and usable 39 in the secure world. The combination of this with "status" allows 40 the various possible combinations of device visibility to be 41 specified. If "secure-status" is not specified it defaults to the 42 same value as "status"; if "status" is not specified either then 43 both default to "okay". This means the following combinations are 44 possible: 45 46 /* Neither specified: default to visible in both S and NS */ 47 secure-status = "okay"; /* visible in both */ 48 status = "okay"; /* visible in both */ 49 status = "okay"; secure-status = "okay"; /* visible in both */ 50 secure-status = "disabled"; /* NS-only */ 51 status = "okay"; secure-status = "disabled"; /* NS-only */ 52 status = "disabled"; secure-status = "okay"; /* S-only */ 53 status = "disabled"; /* disabled in both */ 54 status = "disabled"; secure-status = "disabled"; /* disabled in both */ 55 56The secure-chosen node 57---------------------- 58 59Similar to the /chosen node which serves as a place for passing data 60between firmware and the operating system, the /secure-chosen node may 61be used to pass data to the Secure OS. Only the properties defined 62below may appear in the /secure-chosen node. 63 64- stdout-path : specifies the device to be used by the Secure OS for 65 its console output. The syntax is the same as for /chosen/stdout-path. 66 If the /secure-chosen node exists but the stdout-path property is not 67 present, the Secure OS should not perform any console output. If 68 /secure-chosen does not exist, the Secure OS should use the value of 69 /chosen/stdout-path instead (that is, use the same device as the 70 Normal world OS). 71