[PATCH] docs/system/arm: Document which architecture extensions we emulate

[Peter Maydell]

These days the Arm architecture has a wide range of fine-grained
optional extra architectural features. We implement quite a lot
of these but by no means all of them. Document what we do implement,
so that users can find out without having to dig through back-issues
of our Changelog on the wiki.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
The FEAT_ lists are in the order the features are listed in
the Arm ARM; alternatively we could alphabetize them?
(For M-profile the Arm ARM is using alpha order.)
---
 docs/system/arm/emulation.rst | 98 +++++++++++++++++++++++++++++++++++
 docs/system/target-arm.rst    |  6 +++
 2 files changed, 104 insertions(+)
 create mode 100644 docs/system/arm/emulation.rst

diff --git a/docs/system/arm/emulation.rst b/docs/system/arm/emulation.rst
new file mode 100644
index 00000000000..6c3d7170714
--- /dev/null
+++ b/docs/system/arm/emulation.rst
@@ -0,0 +1,98 @@
+A-profile CPU architecture support
+==================================
+
+QEMU's TCG emulation includes support for the Armv5, Armv6, Armv7 and
+Armv8 versions of the A-profile architecture. It also has support for
+the following architecture extensions:
+
+- The Armv8 Cryptographic Extension
+- The Scalable Vector Extension (SVE)
+- FEAT_SB (Speculation Barrier)
+- FEAT_SSBS (Speculative Store Bypass Safe)
+- FEAT_SPECRES (Speculation restriction instructions)
+- FEAT_SHA512 (Advanced SIMD SHA512 instructions)
+- FEAT_SHA3 (Advanced SIMD SHA3 instructions)
+- FEAT_SM3 (Advanced SIMD SM3 instructions)
+- FEAT_SM4 (Advanced SIMD SM4 instructions)
+- FEAT_LSE (Large System Extensions)
+- FEAT_RDM (Advanced SIMD rounding double multiply accumulate instructions)
+- FEAT_LOR (Limited ordering regions)
+- FEAT_HPDS (Hierarchical permission disables)
+- FEAT_PAN (Privileged access never)
+- FEAT_VMID16 (16-bit VMID)
+- FEAT_VHE (Virtualization Host Extensions)
+- FEAT_PMUv3p1 (PMU Extensions v3.1)
+- FEAT_PAN2 (AT S1E1R and AT S1E1W instruction variants affected by PSTATE.PAN)
+- FEAT_FP16 (Half-precision floating-point data processing)
+- FEAT_DotProd (Advanced SIMD dot product instructions)
+- FEAT_FHM (Floating-point half-precision multiplication instructions)
+- FEAT_UAO (Unprivileged Access Override control)
+- FEAT_DPB (DC CVAP instruction)
+- FEAT_AA32HPD (AArch32 hierarchical permission disables)
+- FEAT_TTCNP (Translation table Common not private translations)
+- FEAT_XNX (Translation table stage 2 Unprivileged Execute-never)
+- FEAT_BF16 (AArch64 BFloat16 instructions)
+- FEAT_AA32BF16 (AArch32 BFloat16 instructions)
+- FEAT_I8MM (AArch64 Int8 matrix multiplication instructions)
+- FEAT_AA32I8MM (AArch32 Int8 matrix multiplication instructions)
+- FEAT_FCMA (Floating-point complex number instructions)
+- FEAT_JSCVT (JavaScript conversion instructions)
+- FEAT_LRCPC (Load-acquire RCpc instructions)
+- FEAT_PAuth (Pointer authentication)
+- FEAT_DIT (Data Independent Timing instructions)
+- FEAT_FlagM (Flag manipulation instructions v2)
+- FEAT_LRCPC2 (Load-acquire RCpc instructions v2)
+- FEAT_TLBIOS (TLB invalidate instructions in Outer Shareable domain)
+- FEAT_TLBIRANGE (TLB invalidate range instructions)
+- FEAT_TTST (Small translation tables)
+- FEAT_SEL2 (Secure EL2)
+- FEAT_PMUv3p4 (PMU Extensions v3.4)
+- FEAT_FlagM2 (Enhancements to flag manipulation instructions)
+- FEAT_FRINTTS (Floating-point to integer instructions)
+- FEAT_BTI (Branch Target Identification)
+- FEAT_RNG (Random number generator)
+- FEAT_MTE (Memory Tagging Extension)
+- FEAT_MTE2 (Memory Tagging Extension)
+
+For information on the specifics of these extensions, please refer
+to the `Armv8-A Arm Architecture Reference Manual
+<https://developer.arm.com/documentation/ddi0487/latest>`_.
+
+When a specific named CPU is being emulated, only those features which
+are present in hardware for that CPU are emulated. (If a feature is
+not in the list above then it is not supported, even if the real
+hardware should have it.) The ``max`` CPU enables all features.
+
+R-profile CPU architecture support
+==================================
+
+QEMU's TCG emulation support for R-profile CPUs is currently limited.
+We emulate only the Cortex-R5 and Cortex-R5F CPUs.
+
+M-profile CPU architecture support
+==================================
+
+QEMU's TCG emulation includes support for Armv6-M, Armv7-M, Armv8-M, and
+Armv8.1-M versions of the M-profile architucture.  It also has support
+for the following architecture extensions:
+
+- FP (Floating-point Extension)
+- FPCXT (FPCXT access instructions)
+- HP (Half-precision floating-point instructions)
+- LOB (Low Overhead loops and Branch future)
+- M (Main Extension)
+- MPU (Memory Protection Unit Extension)
+- PXN (Privileged Execute Never)
+- RAS (Reliability, Serviceability and Availability): "minimum RAS Extension" 
only
+- S (Security Extension)
+- ST (System Timer Extension)
+
+For information on the specifics of these extensions, please refer
+to the `Armv8-M Arm Architecture Reference Manual
+<https://developer.arm.com/documentation/ddi0553/latest>`_.
+
+When a specific named CPU is being emulated, only those features which
+are present in hardware for that CPU are emulated. (If a feature is
+not in the list above then it is not supported, even if the real
+hardware should have it.) There is no equivalent of the ``max`` CPU for
+M-profile.
diff --git a/docs/system/target-arm.rst b/docs/system/target-arm.rst
index edd013c7bbd..8b8547f9a9e 100644
--- a/docs/system/target-arm.rst
+++ b/docs/system/target-arm.rst
@@ -99,6 +99,12 @@ undocumented; you can get a complete list by running
    arm/virt
    arm/xlnx-versal-virt
 
+Emulated CPU architecture support
+=================================
+
+.. toctree::
+   arm/emulation
+
 Arm CPU features
 ================
 
-- 
2.20.1