Merge tag 'docs-6.6' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "Documentation work keeps chugging along; this includes:

   - Work from Carlos Bilbao to integrate rustdoc output into the
     generated HTML documentation. This took some work to figure out how
     to do it without slowing the docs build and without creating people
     who don't have Rust installed, but Carlos got there

   - Move the loongarch and mips architecture documentation under
     Documentation/arch/

   - Some more maintainer documentation from Jakub

  ... plus the usual assortment of updates, translations, and fixes"

* tag 'docs-6.6' of git://git.lwn.net/linux: (56 commits)
  Docu: genericirq.rst: fix irq-example
  input: docs: pxrc: remove reference to phoenix-sim
  Documentation: serial-console: Fix literal block marker
  docs/mm: remove references to hmm_mirror ops and clean typos
  docs/zh_CN: correct regi_chg(),regi_add() to region_chg(),region_add()
  Documentation: Fix typos
  Documentation/ABI: Fix typos
  scripts: kernel-doc: fix macro handling in enums
  scripts: kernel-doc: parse DEFINE_DMA_UNMAP_[ADDR|LEN]
  Documentation: riscv: Update boot image header since EFI stub is supported
  Documentation: riscv: Add early boot document
  Documentation: arm: Add bootargs to the table of added DT parameters
  docs: kernel-parameters: Refer to the correct bitmap function
  doc: update params of memhp_default_state=
  docs: Add book to process/kernel-docs.rst
  docs: sparse: fix invalid link addresses
  docs: vfs: clean up after the iterate() removal
  docs: Add a section on surveys to the researcher guidelines
  docs: move mips under arch
  docs: move loongarch under arch
  ...

5 files changed, 178 insertions, 11 deletions

diff --git a/Documentation/riscv/boot-image-header.rst b/Documentation/riscv/boot-image-header.rst
index d7752533865f..df2ffc173e80 100644
--- a/Documentation/riscv/boot-image-header.rst
+++ b/Documentation/riscv/boot-image-header.rst
@@ -7,9 +7,6 @@ Boot image header in RISC-V Linux
 
 This document only describes the boot image header details for RISC-V Linux.
 
-TODO:
-  Write a complete booting guide.
-
 The following 64-byte header is present in decompressed Linux kernel image::
 
 	u32 code0;		  /* Executable code */
@@ -31,11 +28,11 @@ header in future.
 Notes
 =====
 
-- This header can also be reused to support EFI stub for RISC-V in future. EFI
-  specification needs PE/COFF image header in the beginning of the kernel image
-  in order to load it as an EFI application. In order to support EFI stub,
-  code0 should be replaced with "MZ" magic string and res3(at offset 0x3c) should
-  point to the rest of the PE/COFF header.
+- This header is also reused to support EFI stub for RISC-V. EFI specification
+  needs PE/COFF image header in the beginning of the kernel image in order to
+  load it as an EFI application. In order to support EFI stub, code0 is replaced
+  with "MZ" magic string and res3(at offset 0x3c) points to the rest of the
+  PE/COFF header.
 
 - version field indicate header version number
 
diff --git a/Documentation/riscv/boot.rst b/Documentation/riscv/boot.rst
new file mode 100644
index 000000000000..6077b587a842
--- /dev/null
+++ b/Documentation/riscv/boot.rst
@@ -0,0 +1,169 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============================================
+RISC-V Kernel Boot Requirements and Constraints
+===============================================
+
+:Author: Alexandre Ghiti <alexghiti@rivosinc.com>
+:Date: 23 May 2023
+
+This document describes what the RISC-V kernel expects from bootloaders and
+firmware, and also the constraints that any developer must have in mind when
+touching the early boot process. For the purposes of this document, the
+``early boot process`` refers to any code that runs before the final virtual
+mapping is set up.
+
+Pre-kernel Requirements and Constraints
+=======================================
+
+The RISC-V kernel expects the following of bootloaders and platform firmware:
+
+Register state
+--------------
+
+The RISC-V kernel expects:
+
+  * ``$a0`` to contain the hartid of the current core.
+  * ``$a1`` to contain the address of the devicetree in memory.
+
+CSR state
+---------
+
+The RISC-V kernel expects:
+
+  * ``$satp = 0``: the MMU, if present, must be disabled.
+
+Reserved memory for resident firmware
+-------------------------------------
+
+The RISC-V kernel must not map any resident memory, or memory protected with
+PMPs, in the direct mapping, so the firmware must correctly mark those regions
+as per the devicetree specification and/or the UEFI specification.
+
+Kernel location
+---------------
+
+The RISC-V kernel expects to be placed at a PMD boundary (2MB aligned for rv64
+and 4MB aligned for rv32). Note that the EFI stub will physically relocate the
+kernel if that's not the case.
+
+Hardware description
+--------------------
+
+The firmware can pass either a devicetree or ACPI tables to the RISC-V kernel.
+
+The devicetree is either passed directly to the kernel from the previous stage
+using the ``$a1`` register, or when booting with UEFI, it can be passed using the
+EFI configuration table.
+
+The ACPI tables are passed to the kernel using the EFI configuration table. In
+this case, a tiny devicetree is still created by the EFI stub. Please refer to
+"EFI stub and devicetree" section below for details about this devicetree.
+
+Kernel entry
+------------
+
+On SMP systems, there are 2 methods to enter the kernel:
+
+- ``RISCV_BOOT_SPINWAIT``: the firmware releases all harts in the kernel, one hart
+  wins a lottery and executes the early boot code while the other harts are
+  parked waiting for the initialization to finish. This method is mostly used to
+  support older firmwares without SBI HSM extension and M-mode RISC-V kernel.
+- ``Ordered booting``: the firmware releases only one hart that will execute the
+  initialization phase and then will start all other harts using the SBI HSM
+  extension. The ordered booting method is the preferred booting method for
+  booting the RISC-V kernel because it can support CPU hotplug and kexec.
+
+UEFI
+----
+
+UEFI memory map
+~~~~~~~~~~~~~~~
+
+When booting with UEFI, the RISC-V kernel will use only the EFI memory map to
+populate the system memory.
+
+The UEFI firmware must parse the subnodes of the ``/reserved-memory`` devicetree
+node and abide by the devicetree specification to convert the attributes of
+those subnodes (``no-map`` and ``reusable``) into their correct EFI equivalent
+(refer to section "3.5.4 /reserved-memory and UEFI" of the devicetree
+specification v0.4-rc1).
+
+RISCV_EFI_BOOT_PROTOCOL
+~~~~~~~~~~~~~~~~~~~~~~~
+
+When booting with UEFI, the EFI stub requires the boot hartid in order to pass
+it to the RISC-V kernel in ``$a1``. The EFI stub retrieves the boot hartid using
+one of the following methods:
+
+- ``RISCV_EFI_BOOT_PROTOCOL`` (**preferred**).
+- ``boot-hartid`` devicetree subnode (**deprecated**).
+
+Any new firmware must implement ``RISCV_EFI_BOOT_PROTOCOL`` as the devicetree
+based approach is deprecated now.
+
+Early Boot Requirements and Constraints
+=======================================
+
+The RISC-V kernel's early boot process operates under the following constraints:
+
+EFI stub and devicetree
+-----------------------
+
+When booting with UEFI, the devicetree is supplemented (or created) by the EFI
+stub with the same parameters as arm64 which are described at the paragraph
+"UEFI kernel support on ARM" in Documentation/arch/arm/uefi.rst.
+
+Virtual mapping installation
+----------------------------
+
+The installation of the virtual mapping is done in 2 steps in the RISC-V kernel:
+
+1. ``setup_vm()`` installs a temporary kernel mapping in ``early_pg_dir`` which
+   allows discovery of the system memory. Only the kernel text/data are mapped
+   at this point. When establishing this mapping, no allocation can be done
+   (since the system memory is not known yet), so ``early_pg_dir`` page table is
+   statically allocated (using only one table for each level).
+
+2. ``setup_vm_final()`` creates the final kernel mapping in ``swapper_pg_dir``
+   and takes advantage of the discovered system memory to create the linear
+   mapping. When establishing this mapping, the kernel can allocate memory but
+   cannot access it directly (since the direct mapping is not present yet), so
+   it uses temporary mappings in the fixmap region to be able to access the
+   newly allocated page table levels.
+
+For ``virt_to_phys()`` and ``phys_to_virt()`` to be able to correctly convert
+direct mapping addresses to physical addresses, they need to know the start of
+the DRAM. This happens after step 1, right before step 2 installs the direct
+mapping (see ``setup_bootmem()`` function in arch/riscv/mm/init.c). Any usage of
+those macros before the final virtual mapping is installed must be carefully
+examined.
+
+Devicetree mapping via fixmap
+-----------------------------
+
+As the ``reserved_mem`` array is initialized with virtual addresses established
+by ``setup_vm()``, and used with the mapping established by
+``setup_vm_final()``, the RISC-V kernel uses the fixmap region to map the
+devicetree. This ensures that the devicetree remains accessible by both virtual
+mappings.
+
+Pre-MMU execution
+-----------------
+
+A few pieces of code need to run before even the first virtual mapping is
+established. These are the installation of the first virtual mapping itself,
+patching of early alternatives and the early parsing of the kernel command line.
+That code must be very carefully compiled as:
+
+- ``-fno-pie``: This is needed for relocatable kernels which use ``-fPIE``,
+  since otherwise, any access to a global symbol would go through the GOT which
+  is only relocated virtually.
+- ``-mcmodel=medany``: Any access to a global symbol must be PC-relative to
+  avoid any relocations to happen before the MMU is setup.
+- *all* instrumentation must also be disabled (that includes KASAN, ftrace and
+  others).
+
+As using a symbol from a different compilation unit requires this unit to be
+compiled with those flags, we advise, as much as possible, not to use external
+symbols.
diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst
index 933c715065d6..20eff9650da9 100644
--- a/Documentation/riscv/hwprobe.rst
+++ b/Documentation/riscv/hwprobe.rst
@@ -88,11 +88,11 @@ The following keys are defined:
     always extremely slow.
 
   * :c:macro:`RISCV_HWPROBE_MISALIGNED_SLOW`: Misaligned accesses are supported
-    in hardware, but are slower than the cooresponding aligned accesses
+    in hardware, but are slower than the corresponding aligned accesses
     sequences.
 
   * :c:macro:`RISCV_HWPROBE_MISALIGNED_FAST`: Misaligned accesses are supported
-    in hardware and are faster than the cooresponding aligned accesses
+    in hardware and are faster than the corresponding aligned accesses
     sequences.
 
   * :c:macro:`RISCV_HWPROBE_MISALIGNED_UNSUPPORTED`: Misaligned accesses are
diff --git a/Documentation/riscv/index.rst b/Documentation/riscv/index.rst
index 81cf6e616476..4dab0cb4b900 100644
--- a/Documentation/riscv/index.rst
+++ b/Documentation/riscv/index.rst
@@ -6,6 +6,7 @@ RISC-V architecture
     :maxdepth: 1
 
     acpi
+    boot
     boot-image-header
     vm-layout
     hwprobe
diff --git a/Documentation/riscv/vector.rst b/Documentation/riscv/vector.rst
index 165b7ed0ac4f..75dd88a62e1d 100644
--- a/Documentation/riscv/vector.rst
+++ b/Documentation/riscv/vector.rst
@@ -13,7 +13,7 @@ order to support the use of the RISC-V Vector Extension.
 Two new prctl() calls are added to allow programs to manage the enablement
 status for the use of Vector in userspace. The intended usage guideline for
 these interfaces is to give init systems a way to modify the availability of V
-for processes running under its domain. Calling thess interfaces is not
+for processes running under its domain. Calling these interfaces is not
 recommended in libraries routines because libraries should not override policies
 configured from the parant process. Also, users must noted that these interfaces
 are not portable to non-Linux, nor non-RISC-V environments, so it is discourage