1 * ARM Secure world bindings 2 3 ARM CPUs with TrustZone support have two distinct address spaces, 4 "Normal" and "Secure". Most devicetree consumers (including the Linux 5 kernel) are not TrustZone aware and run entirely in either the Normal 6 world or the Secure world. However some devicetree consumers are 7 TrustZone aware and need to be able to determine whether devices are 8 visible only in the Secure address space, only in the Normal address 9 space, or visible in both. (One example of that situation would be a 10 virtual machine which boots Secure firmware and wants to tell the 11 firmware about the layout of the machine via devicetree.) 12 13 The general principle of the naming scheme for Secure world bindings 14 is that any property that needs a different value in the Secure world 15 can be supported by prefixing the property name with "secure-". So for 16 instance "secure-foo" would override "foo". For property names with 17 a vendor prefix, the Secure variant of "vendor,foo" would be 18 "vendor,secure-foo". If there is no "secure-" property then the Secure 19 world value is the same as specified for the Normal world by the 20 non-prefixed property. However, only the properties listed below may 21 validly have "secure-" versions; this list will be enlarged on a 22 case-by-case basis. 23 24 Defining the bindings in this way means that a device tree which has 25 been annotated to indicate the presence of Secure-only devices can 26 still be processed unmodified by existing Non-secure software (and in 27 particular by the kernel). 28 29 Note that it is still valid for bindings intended for purely Secure 30 world consumers (like kernels that run entirely in Secure) to simply 31 describe the view of Secure world using the standard bindings. These 32 secure- bindings only need to be used where both the Secure and Normal 33 world views need to be described in a single device tree. 34 35 Valid 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 56 The secure-chosen node 57 ---------------------- 58 59 Similar to the /chosen node which serves as a place for passing data 60 between firmware and the operating system, the /secure-chosen node may 61 be used to pass data to the Secure OS. Only the properties defined 62 below 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).
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.