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Some platforms may use a single device tree to describe two address
spaces, as described in d9f43babb9 ("Documentation: dt: Add bindings
for Secure-only devices"). For these platforms it makes sense to define
a secure counterpart of /chosen, namely: /secure-chosen. This new node
is meant to be used by the secure firmware to pass data to the secure
OS. Only the stdout-path property is supported for now.
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>
71 lines
3.6 KiB
Plaintext
71 lines
3.6 KiB
Plaintext
* ARM Secure world bindings
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ARM CPUs with TrustZone support have two distinct address spaces,
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"Normal" and "Secure". Most devicetree consumers (including the Linux
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kernel) are not TrustZone aware and run entirely in either the Normal
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world or the Secure world. However some devicetree consumers are
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TrustZone aware and need to be able to determine whether devices are
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visible only in the Secure address space, only in the Normal address
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space, or visible in both. (One example of that situation would be a
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virtual machine which boots Secure firmware and wants to tell the
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firmware about the layout of the machine via devicetree.)
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The general principle of the naming scheme for Secure world bindings
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is that any property that needs a different value in the Secure world
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can be supported by prefixing the property name with "secure-". So for
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instance "secure-foo" would override "foo". For property names with
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a vendor prefix, the Secure variant of "vendor,foo" would be
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"vendor,secure-foo". If there is no "secure-" property then the Secure
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world value is the same as specified for the Normal world by the
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non-prefixed property. However, only the properties listed below may
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validly have "secure-" versions; this list will be enlarged on a
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case-by-case basis.
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Defining the bindings in this way means that a device tree which has
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been annotated to indicate the presence of Secure-only devices can
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still be processed unmodified by existing Non-secure software (and in
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particular by the kernel).
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Note that it is still valid for bindings intended for purely Secure
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world consumers (like kernels that run entirely in Secure) to simply
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describe the view of Secure world using the standard bindings. These
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secure- bindings only need to be used where both the Secure and Normal
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world views need to be described in a single device tree.
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Valid Secure world properties
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-----------------------------
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- secure-status : specifies whether the device is present and usable
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in the secure world. The combination of this with "status" allows
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the various possible combinations of device visibility to be
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specified. If "secure-status" is not specified it defaults to the
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same value as "status"; if "status" is not specified either then
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both default to "okay". This means the following combinations are
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possible:
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/* Neither specified: default to visible in both S and NS */
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secure-status = "okay"; /* visible in both */
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status = "okay"; /* visible in both */
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status = "okay"; secure-status = "okay"; /* visible in both */
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secure-status = "disabled"; /* NS-only */
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status = "okay"; secure-status = "disabled"; /* NS-only */
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status = "disabled"; secure-status = "okay"; /* S-only */
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status = "disabled"; /* disabled in both */
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status = "disabled"; secure-status = "disabled"; /* disabled in both */
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The secure-chosen node
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----------------------
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Similar to the /chosen node which serves as a place for passing data
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between firmware and the operating system, the /secure-chosen node may
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be used to pass data to the Secure OS. Only the properties defined
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below may appear in the /secure-chosen node.
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- stdout-path : specifies the device to be used by the Secure OS for
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its console output. The syntax is the same as for /chosen/stdout-path.
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If the /secure-chosen node exists but the stdout-path property is not
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present, the Secure OS should not perform any console output. If
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/secure-chosen does not exist, the Secure OS should use the value of
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/chosen/stdout-path instead (that is, use the same device as the
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Normal world OS).
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