Merge tag 'docs-5.7' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "This has been a busy cycle for documentation work.

  Highlights include:

   - Lots of RST conversion work by Mauro, Daniel ALmeida, and others.
     Maybe someday we'll get to the end of this stuff...maybe...

   - Some organizational work to bring some order to the core-api
     manual.

   - Various new docs and additions to the existing documentation.

   - Typo fixes, warning fixes, ..."

* tag 'docs-5.7' of git://git.lwn.net/linux: (123 commits)
  Documentation: x86: exception-tables: document CONFIG_BUILDTIME_TABLE_SORT
  MAINTAINERS: adjust to filesystem doc ReST conversion
  docs: deprecated.rst: Add BUG()-family
  doc: zh_CN: add translation for virtiofs
  doc: zh_CN: index files in filesystems subdirectory
  docs: locking: Drop :c:func: throughout
  docs: locking: Add 'need' to hardirq section
  docs: conf.py: avoid thousands of duplicate label warning on Sphinx
  docs: prevent warnings due to autosectionlabel
  docs: fix reference to core-api/namespaces.rst
  docs: fix pointers to io-mapping.rst and io_ordering.rst files
  Documentation: Better document the softlockup_panic sysctl
  docs: hw-vuln: tsx_async_abort.rst: get rid of an unused ref
  docs: perf: imx-ddr.rst: get rid of a warning
  docs: filesystems: fuse.rst: supress a Sphinx warning
  docs: translations: it: avoid duplicate refs at programming-language.rst
  docs: driver.rst: supress two ReSt warnings
  docs: trace: events.rst: convert some new stuff to ReST format
  Documentation: Add io_ordering.rst to driver-api manual
  Documentation: Add io-mapping.rst to driver-api manual
  ...

8 files changed, 411 insertions, 66 deletions

diff --git a/Documentation/driver-api/80211/mac80211-advanced.rst b/Documentation/driver-api/80211/mac80211-advanced.rst
index 9f1c5bb7ac35..24cb64b3b715 100644
--- a/Documentation/driver-api/80211/mac80211-advanced.rst
+++ b/Documentation/driver-api/80211/mac80211-advanced.rst
@@ -272,8 +272,8 @@ STA information lifetime rules
 .. kernel-doc:: net/mac80211/sta_info.c
    :doc: STA information lifetime rules
 
-Aggregation
-===========
+Aggregation Functions
+=====================
 
 .. kernel-doc:: net/mac80211/sta_info.h
    :functions: sta_ampdu_mlme
@@ -284,8 +284,8 @@ Aggregation
 .. kernel-doc:: net/mac80211/sta_info.h
    :functions: tid_ampdu_rx
 
-Synchronisation
-===============
+Synchronisation Functions
+=========================
 
 TBD
 
diff --git a/Documentation/driver-api/dmaengine/index.rst b/Documentation/driver-api/dmaengine/index.rst
index b9df904d0a79..bdc45d8b4cfb 100644
--- a/Documentation/driver-api/dmaengine/index.rst
+++ b/Documentation/driver-api/dmaengine/index.rst
@@ -5,8 +5,8 @@ DMAEngine documentation
 DMAEngine documentation provides documents for various aspects of DMAEngine
 framework.
 
-DMAEngine documentation
------------------------
+DMAEngine development documentation
+-----------------------------------
 
 This book helps with DMAengine internal APIs and guide for DMAEngine device
 driver writers.
diff --git a/Documentation/driver-api/driver-model/driver.rst b/Documentation/driver-api/driver-model/driver.rst
index baa6a85c8287..63887b813005 100644
--- a/Documentation/driver-api/driver-model/driver.rst
+++ b/Documentation/driver-api/driver-model/driver.rst
@@ -210,7 +210,7 @@ probed.
 While the typical use case for sync_state() is to have the kernel cleanly take
 over management of devices from the bootloader, the usage of sync_state() is
 not restricted to that. Use it whenever it makes sense to take an action after
-all the consumers of a device have probed.
+all the consumers of a device have probed::
 
 	int 	(*remove)	(struct device *dev);
 
diff --git a/Documentation/driver-api/edid.rst b/Documentation/driver-api/edid.rst
deleted file mode 100644
index b1b5acd501ed..000000000000
--- a/Documentation/driver-api/edid.rst
+++ /dev/null
@@ -1,58 +0,0 @@
-.. SPDX-License-Identifier: GPL-2.0
-
-====
-EDID
-====
-
-In the good old days when graphics parameters were configured explicitly
-in a file called xorg.conf, even broken hardware could be managed.
-
-Today, with the advent of Kernel Mode Setting, a graphics board is
-either correctly working because all components follow the standards -
-or the computer is unusable, because the screen remains dark after
-booting or it displays the wrong area. Cases when this happens are:
-- The graphics board does not recognize the monitor.
-- The graphics board is unable to detect any EDID data.
-- The graphics board incorrectly forwards EDID data to the driver.
-- The monitor sends no or bogus EDID data.
-- A KVM sends its own EDID data instead of querying the connected monitor.
-Adding the kernel parameter "nomodeset" helps in most cases, but causes
-restrictions later on.
-
-As a remedy for such situations, the kernel configuration item
-CONFIG_DRM_LOAD_EDID_FIRMWARE was introduced. It allows to provide an
-individually prepared or corrected EDID data set in the /lib/firmware
-directory from where it is loaded via the firmware interface. The code
-(see drivers/gpu/drm/drm_edid_load.c) contains built-in data sets for
-commonly used screen resolutions (800x600, 1024x768, 1280x1024, 1600x1200,
-1680x1050, 1920x1080) as binary blobs, but the kernel source tree does
-not contain code to create these data. In order to elucidate the origin
-of the built-in binary EDID blobs and to facilitate the creation of
-individual data for a specific misbehaving monitor, commented sources
-and a Makefile environment are given here.
-
-To create binary EDID and C source code files from the existing data
-material, simply type "make".
-
-If you want to create your own EDID file, copy the file 1024x768.S,
-replace the settings with your own data and add a new target to the
-Makefile. Please note that the EDID data structure expects the timing
-values in a different way as compared to the standard X11 format.
-
-X11:
-  HTimings:
-    hdisp hsyncstart hsyncend htotal
-  VTimings:
-    vdisp vsyncstart vsyncend vtotal
-
-EDID::
-
-  #define XPIX hdisp
-  #define XBLANK htotal-hdisp
-  #define XOFFSET hsyncstart-hdisp
-  #define XPULSE hsyncend-hsyncstart
-
-  #define YPIX vdisp
-  #define YBLANK vtotal-vdisp
-  #define YOFFSET vsyncstart-vdisp
-  #define YPULSE vsyncend-vsyncstart
diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst
index 0ebe205efd0c..d4e78cb3ef4d 100644
--- a/Documentation/driver-api/index.rst
+++ b/Documentation/driver-api/index.rst
@@ -17,6 +17,7 @@ available subsections can be seen below.
    driver-model/index
    basics
    infrastructure
+   ioctl
    early-userspace/index
    pm/index
    clk
@@ -74,11 +75,12 @@ available subsections can be seen below.
    connector
    console
    dcdbas
-   edid
    eisa
    ipmb
    isa
    isapnp
+   io-mapping
+   io_ordering
    generic-counter
    lightnvm-pblk
    memory-devices/index
diff --git a/Documentation/driver-api/io-mapping.rst b/Documentation/driver-api/io-mapping.rst
new file mode 100644
index 000000000000..a966239f04e4
--- /dev/null
+++ b/Documentation/driver-api/io-mapping.rst
@@ -0,0 +1,97 @@
+========================
+The io_mapping functions
+========================
+
+API
+===
+
+The io_mapping functions in linux/io-mapping.h provide an abstraction for
+efficiently mapping small regions of an I/O device to the CPU. The initial
+usage is to support the large graphics aperture on 32-bit processors where
+ioremap_wc cannot be used to statically map the entire aperture to the CPU
+as it would consume too much of the kernel address space.
+
+A mapping object is created during driver initialization using::
+
+	struct io_mapping *io_mapping_create_wc(unsigned long base,
+						unsigned long size)
+
+'base' is the bus address of the region to be made
+mappable, while 'size' indicates how large a mapping region to
+enable. Both are in bytes.
+
+This _wc variant provides a mapping which may only be used
+with the io_mapping_map_atomic_wc or io_mapping_map_wc.
+
+With this mapping object, individual pages can be mapped either atomically
+or not, depending on the necessary scheduling environment. Of course, atomic
+maps are more efficient::
+
+	void *io_mapping_map_atomic_wc(struct io_mapping *mapping,
+				       unsigned long offset)
+
+'offset' is the offset within the defined mapping region.
+Accessing addresses beyond the region specified in the
+creation function yields undefined results. Using an offset
+which is not page aligned yields an undefined result. The
+return value points to a single page in CPU address space.
+
+This _wc variant returns a write-combining map to the
+page and may only be used with mappings created by
+io_mapping_create_wc
+
+Note that the task may not sleep while holding this page
+mapped.
+
+::
+
+	void io_mapping_unmap_atomic(void *vaddr)
+
+'vaddr' must be the value returned by the last
+io_mapping_map_atomic_wc call. This unmaps the specified
+page and allows the task to sleep once again.
+
+If you need to sleep while holding the lock, you can use the non-atomic
+variant, although they may be significantly slower.
+
+::
+
+	void *io_mapping_map_wc(struct io_mapping *mapping,
+				unsigned long offset)
+
+This works like io_mapping_map_atomic_wc except it allows
+the task to sleep while holding the page mapped.
+
+
+::
+
+	void io_mapping_unmap(void *vaddr)
+
+This works like io_mapping_unmap_atomic, except it is used
+for pages mapped with io_mapping_map_wc.
+
+At driver close time, the io_mapping object must be freed::
+
+	void io_mapping_free(struct io_mapping *mapping)
+
+Current Implementation
+======================
+
+The initial implementation of these functions uses existing mapping
+mechanisms and so provides only an abstraction layer and no new
+functionality.
+
+On 64-bit processors, io_mapping_create_wc calls ioremap_wc for the whole
+range, creating a permanent kernel-visible mapping to the resource. The
+map_atomic and map functions add the requested offset to the base of the
+virtual address returned by ioremap_wc.
+
+On 32-bit processors with HIGHMEM defined, io_mapping_map_atomic_wc uses
+kmap_atomic_pfn to map the specified page in an atomic fashion;
+kmap_atomic_pfn isn't really supposed to be used with device pages, but it
+provides an efficient mapping for this usage.
+
+On 32-bit processors without HIGHMEM defined, io_mapping_map_atomic_wc and
+io_mapping_map_wc both use ioremap_wc, a terribly inefficient function which
+performs an IPI to inform all processors about the new mapping. This results
+in a significant performance penalty.
diff --git a/Documentation/driver-api/io_ordering.rst b/Documentation/driver-api/io_ordering.rst
new file mode 100644
index 000000000000..2ab303ce9a0d
--- /dev/null
+++ b/Documentation/driver-api/io_ordering.rst
@@ -0,0 +1,51 @@
+==============================================
+Ordering I/O writes to memory-mapped addresses
+==============================================
+
+On some platforms, so-called memory-mapped I/O is weakly ordered.  On such
+platforms, driver writers are responsible for ensuring that I/O writes to
+memory-mapped addresses on their device arrive in the order intended.  This is
+typically done by reading a 'safe' device or bridge register, causing the I/O
+chipset to flush pending writes to the device before any reads are posted.  A
+driver would usually use this technique immediately prior to the exit of a
+critical section of code protected by spinlocks.  This would ensure that
+subsequent writes to I/O space arrived only after all prior writes (much like a
+memory barrier op, mb(), only with respect to I/O).
+
+A more concrete example from a hypothetical device driver::
+
+		...
+	CPU A:  spin_lock_irqsave(&dev_lock, flags)
+	CPU A:  val = readl(my_status);
+	CPU A:  ...
+	CPU A:  writel(newval, ring_ptr);
+	CPU A:  spin_unlock_irqrestore(&dev_lock, flags)
+		...
+	CPU B:  spin_lock_irqsave(&dev_lock, flags)
+	CPU B:  val = readl(my_status);
+	CPU B:  ...
+	CPU B:  writel(newval2, ring_ptr);
+	CPU B:  spin_unlock_irqrestore(&dev_lock, flags)
+		...
+
+In the case above, the device may receive newval2 before it receives newval,
+which could cause problems.  Fixing it is easy enough though::
+
+		...
+	CPU A:  spin_lock_irqsave(&dev_lock, flags)
+	CPU A:  val = readl(my_status);
+	CPU A:  ...
+	CPU A:  writel(newval, ring_ptr);
+	CPU A:  (void)readl(safe_register); /* maybe a config register? */
+	CPU A:  spin_unlock_irqrestore(&dev_lock, flags)
+		...
+	CPU B:  spin_lock_irqsave(&dev_lock, flags)
+	CPU B:  val = readl(my_status);
+	CPU B:  ...
+	CPU B:  writel(newval2, ring_ptr);
+	CPU B:  (void)readl(safe_register); /* maybe a config register? */
+	CPU B:  spin_unlock_irqrestore(&dev_lock, flags)
+
+Here, the reads from safe_register will cause the I/O chipset to flush any
+pending writes before actually posting the read to the chipset, preventing
+possible data corruption.
diff --git a/Documentation/driver-api/ioctl.rst b/Documentation/driver-api/ioctl.rst
new file mode 100644
index 000000000000..c455db0e1627
--- /dev/null
+++ b/Documentation/driver-api/ioctl.rst
@@ -0,0 +1,253 @@
+======================
+ioctl based interfaces
+======================
+
+ioctl() is the most common way for applications to interface
+with device drivers. It is flexible and easily extended by adding new
+commands and can be passed through character devices, block devices as
+well as sockets and other special file descriptors.
+
+However, it is also very easy to get ioctl command definitions wrong,
+and hard to fix them later without breaking existing applications,
+so this documentation tries to help developers get it right.
+
+Command number definitions
+==========================
+
+The command number, or request number, is the second argument passed to
+the ioctl system call. While this can be any 32-bit number that uniquely
+identifies an action for a particular driver, there are a number of
+conventions around defining them.
+
+``include/uapi/asm-generic/ioctl.h`` provides four macros for defining
+ioctl commands that follow modern conventions: ``_IO``, ``_IOR``,
+``_IOW``, and ``_IOWR``. These should be used for all new commands,
+with the correct parameters:
+
+_IO/_IOR/_IOW/_IOWR
+   The macro name specifies how the argument will be used.  It may be a
+   pointer to data to be passed into the kernel (_IOW), out of the kernel
+   (_IOR), or both (_IOWR).  _IO can indicate either commands with no
+   argument or those passing an integer value instead of a pointer.
+   It is recommended to only use _IO for commands without arguments,
+   and use pointers for passing data.
+
+type
+   An 8-bit number, often a character literal, specific to a subsystem
+   or driver, and listed in :doc:`../userspace-api/ioctl/ioctl-number`
+
+nr
+  An 8-bit number identifying the specific command, unique for a give
+  value of 'type'
+
+data_type
+  The name of the data type pointed to by the argument, the command number
+  encodes the ``sizeof(data_type)`` value in a 13-bit or 14-bit integer,
+  leading to a limit of 8191 bytes for the maximum size of the argument.
+  Note: do not pass sizeof(data_type) type into _IOR/_IOW/IOWR, as that
+  will lead to encoding sizeof(sizeof(data_type)), i.e. sizeof(size_t).
+  _IO does not have a data_type parameter.
+
+
+Interface versions
+==================
+
+Some subsystems use version numbers in data structures to overload
+commands with different interpretations of the argument.
+
+This is generally a bad idea, since changes to existing commands tend
+to break existing applications.
+
+A better approach is to add a new ioctl command with a new number. The
+old command still needs to be implemented in the kernel for compatibility,
+but this can be a wrapper around the new implementation.
+
+Return code
+===========
+
+ioctl commands can return negative error codes as documented in errno(3);
+these get turned into errno values in user space. On success, the return
+code should be zero. It is also possible but not recommended to return
+a positive 'long' value.
+
+When the ioctl callback is called with an unknown command number, the
+handler returns either -ENOTTY or -ENOIOCTLCMD, which also results in
+-ENOTTY being returned from the system call. Some subsystems return
+-ENOSYS or -EINVAL here for historic reasons, but this is wrong.
+
+Prior to Linux 5.5, compat_ioctl handlers were required to return
+-ENOIOCTLCMD in order to use the fallback conversion into native
+commands. As all subsystems are now responsible for handling compat
+mode themselves, this is no longer needed, but it may be important to
+consider when backporting bug fixes to older kernels.
+
+Timestamps
+==========
+
+Traditionally, timestamps and timeout values are passed as ``struct
+timespec`` or ``struct timeval``, but these are problematic because of
+incompatible definitions of these structures in user space after the
+move to 64-bit time_t.
+
+The ``struct __kernel_timespec`` type can be used instead to be embedded
+in other data structures when separate second/nanosecond values are
+desired, or passed to user space directly. This is still not ideal though,
+as the structure matches neither the kernel's timespec64 nor the user
+space timespec exactly. The get_timespec64() and put_timespec64() helper
+functions can be used to ensure that the layout remains compatible with
+user space and the padding is treated correctly.
+
+As it is cheap to convert seconds to nanoseconds, but the opposite
+requires an expensive 64-bit division, a simple __u64 nanosecond value
+can be simpler and more efficient.
+
+Timeout values and timestamps should ideally use CLOCK_MONOTONIC time,
+as returned by ktime_get_ns() or ktime_get_ts64().  Unlike
+CLOCK_REALTIME, this makes the timestamps immune from jumping backwards
+or forwards due to leap second adjustments and clock_settime() calls.
+
+ktime_get_real_ns() can be used for CLOCK_REALTIME timestamps that
+need to be persistent across a reboot or between multiple machines.
+
+32-bit compat mode
+==================
+
+In order to support 32-bit user space running on a 64-bit machine, each
+subsystem or driver that implements an ioctl callback handler must also
+implement the corresponding compat_ioctl handler.
+
+As long as all the rules for data structures are followed, this is as
+easy as setting the .compat_ioctl pointer to a helper function such as
+compat_ptr_ioctl() or blkdev_compat_ptr_ioctl().
+
+compat_ptr()
+------------
+
+On the s390 architecture, 31-bit user space has ambiguous representations
+for data pointers, with the upper bit being ignored. When running such
+a process in compat mode, the compat_ptr() helper must be used to
+clear the upper bit of a compat_uptr_t and turn it into a valid 64-bit
+pointer.  On other architectures, this macro only performs a cast to a
+``void __user *`` pointer.
+
+In an compat_ioctl() callback, the last argument is an unsigned long,
+which can be interpreted as either a pointer or a scalar depending on
+the command. If it is a scalar, then compat_ptr() must not be used, to
+ensure that the 64-bit kernel behaves the same way as a 32-bit kernel
+for arguments with the upper bit set.
+
+The compat_ptr_ioctl() helper can be used in place of a custom
+compat_ioctl file operation for drivers that only take arguments that
+are pointers to compatible data structures.
+
+Structure layout
+----------------
+
+Compatible data structures have the same layout on all architectures,
+avoiding all problematic members:
+
+* ``long`` and ``unsigned long`` are the size of a register, so
+  they can be either 32-bit or 64-bit wide and cannot be used in portable
+  data structures. Fixed-length replacements are ``__s32``, ``__u32``,
+  ``__s64`` and ``__u64``.
+
+* Pointers have the same problem, in addition to requiring the
+  use of compat_ptr(). The best workaround is to use ``__u64``
+  in place of pointers, which requires a cast to ``uintptr_t`` in user
+  space, and the use of u64_to_user_ptr() in the kernel to convert
+  it back into a user pointer.
+
+* On the x86-32 (i386) architecture, the alignment of 64-bit variables
+  is only 32-bit, but they are naturally aligned on most other
+  architectures including x86-64. This means a structure like::
+
+    struct foo {
+        __u32 a;
+        __u64 b;
+        __u32 c;
+    };
+
+  has four bytes of padding between a and b on x86-64, plus another four
+  bytes of padding at the end, but no padding on i386, and it needs a
+  compat_ioctl conversion handler to translate between the two formats.
+
+  To avoid this problem, all structures should have their members
+  naturally aligned, or explicit reserved fields added in place of the
+  implicit padding. The ``pahole`` tool can be used for checking the
+  alignment.
+
+* On ARM OABI user space, structures are padded to multiples of 32-bit,
+  making some structs incompatible with modern EABI kernels if they
+  do not end on a 32-bit boundary.
+
+* On the m68k architecture, struct members are not guaranteed to have an
+  alignment greater than 16-bit, which is a problem when relying on
+  implicit padding.
+
+* Bitfields and enums generally work as one would expect them to,
+  but some properties of them are implementation-defined, so it is better
+  to avoid them completely in ioctl interfaces.
+
+* ``char`` members can be either signed or unsigned, depending on
+  the architecture, so the __u8 and __s8 types should be used for 8-bit
+  integer values, though char arrays are clearer for fixed-length strings.
+
+Information leaks
+=================
+
+Uninitialized data must not be copied back to user space, as this can
+cause an information leak, which can be used to defeat kernel address
+space layout randomization (KASLR), helping in an attack.
+
+For this reason (and for compat support) it is best to avoid any
+implicit padding in data structures.  Where there is implicit padding
+in an existing structure, kernel drivers must be careful to fully
+initialize an instance of the structure before copying it to user
+space.  This is usually done by calling memset() before assigning to
+individual members.
+
+Subsystem abstractions
+======================
+
+While some device drivers implement their own ioctl function, most
+subsystems implement the same command for multiple drivers.  Ideally the
+subsystem has an .ioctl() handler that copies the arguments from and
+to user space, passing them into subsystem specific callback functions
+through normal kernel pointers.
+
+This helps in various ways:
+
+* Applications written for one driver are more likely to work for
+  another one in the same subsystem if there are no subtle differences
+  in the user space ABI.
+
+* The complexity of user space access and data structure layout is done
+  in one place, reducing the potential for implementation bugs.
+
+* It is more likely to be reviewed by experienced developers
+  that can spot problems in the interface when the ioctl is shared
+  between multiple drivers than when it is only used in a single driver.
+
+Alternatives to ioctl
+=====================
+
+There are many cases in which ioctl is not the best solution for a
+problem. Alternatives include:
+
+* System calls are a better choice for a system-wide feature that
+  is not tied to a physical device or constrained by the file system
+  permissions of a character device node
+
+* netlink is the preferred way of configuring any network related
+  objects through sockets.
+
+* debugfs is used for ad-hoc interfaces for debugging functionality
+  that does not need to be exposed as a stable interface to applications.
+
+* sysfs is a good way to expose the state of an in-kernel object
+  that is not tied to a file descriptor.
+
+* configfs can be used for more complex configuration than sysfs
+
+* A custom file system can provide extra flexibility with a simple
+  user interface but adds a lot of complexity to the implementation.