S-mode software needs a way to know memory used by SBI firmware so
that it can correctly mark such memory as reserved.

Related discussion:
https://github.com/riscv/opensbi/issues/103

Signed-off-by: Bin Meng <bmeng.cn@...>

---

riscv-sbi.adoc | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 65 insertions(+)

diff --git a/riscv-sbi.adoc b/riscv-sbi.adoc
index 37d0791..c9dba7c 100644
--- a/riscv-sbi.adoc
+++ b/riscv-sbi.adoc
@@ -592,6 +592,71 @@ state of the hart at the time of return value verification.
| sbi_hart_get_status | 2 | 0x48534D
|===

+== Physical Memory Protection Extension, Extension ID: 0x504D50 (PMP)
+The Physical Memory Protection Extension introduces a set of functions that
+allow the supervisor to request higher privilege mode to return information
+of the memory regions protected by the SBI firmware via the PMP unit.
+
+Every memory region protected by the SBI firmware can be described by a C
+structure (or descriptor) below:
+
+[source, C]
+----
+struct pmp_fw_prot_desc {
+ unsigned long base;
+ unsigned long size;
+};
+----
+
+If there are mutiple memory regions protected, multiple descriptors should
+be used with each one describing a single memory region.
+
+[source, C]
+----
+struct sbiret sbi_get_fw_prot_desc_size()
+----
+*Returns* the size of memory (in bytes) required to describe the protected
+memory regions by the SBI firmware via PMP through sbiret.value, or one of
+the following possible SBI error codes through sbiret.error.
+
+[cols="<,>",options="header,compact"]
+|===
+| Error code | Description
+| SBI_SUCCESS | The size of memory (in bytes) required to +
+ describe the protected memory regions by the SBI +
+ firmware via PMP is written to sbiret.value. +
+ The size should be multiple of one descriptor +
+ size, that is sizeof(struct pmp_fw_prot_desc). +
+ If no memory region is protected, zero is set +
+ to sbiret.value.
+| SBI_ERR_NOT_SUPPORTED | PMP is not available on this platform.
+|===
+
+[source, C]
+----
+struct sbiret sbi_get_fw_prot_desc(struct pmp_fw_prot_desc *desc)
+----
+*Returns* one of the following possible SBI error codes through sbiret.error.
+
+[cols="<,>",options="header,compact"]
+|===
+| Error code | Description
+| SBI_SUCCESS | The physical address of RAM pointed by desc +
+ where memory region information is to be written +
+ are filled in by SBI firmware, one after another +
+ if multiple memory regions are protected.
+| SBI_ERR_NOT_SUPPORTED | PMP is not available on this platform.
+|===
+
+=== PMP Function Listing
+
+[cols="<,,>",options="header,compact"]
+|===
+| Function Name | Function ID | Extension ID
+| sbi_get_fw_prot_desc_size | 0 | 0x504D50
+| sbi_get_fw_prot_desc | 1 | 0x504D50
+|===
+
== Experimental SBI Extension Space, Extension IDs 0x0800000 through 0x08FFFFFF

No management.
--
2.7.4