path: root/Documentation/feature-removal-schedule.txt

The following is a list of files and features that are going to be
removed in the kernel source tree.  Every entry should contain what
exactly is going away, why it is happening, and who is going to be doing
the work.  When the feature is removed from the kernel, it should also
be removed from this file.  The suggested deprecation period is 3 releases.

---------------------------

What:	ddebug_query="query" boot cmdline param
When:	v3.8
Why:	obsoleted by dyndbg="query" and module.dyndbg="query"
Who:	Jim Cromie <jim.cromie@gmail.com>, Jason Baron <jbaron@redhat.com>

---------------------------

What: /proc/sys/vm/nr_pdflush_threads
When: 2012
Why: Since pdflush is deprecated, the interface exported in /proc/sys/vm/
     should be removed.
Who: Wanpeng Li <liwp@linux.vnet.ibm.com>

---------------------------

What:	CONFIG_APM_CPU_IDLE, and its ability to call APM BIOS in idle
When:	2012
Why:	This optional sub-feature of APM is of dubious reliability,
	and ancient APM laptops are likely better served by calling HLT.
	Deleting CONFIG_APM_CPU_IDLE allows x86 to stop exporting
	the pm_idle function pointer to modules.
Who:	Len Brown <len.brown@intel.com>

----------------------------

What:	x86_32 "no-hlt" cmdline param
When:	2012
Why:	remove a branch from idle path, simplify code used by everybody.
	This option disabled the use of HLT in idle and machine_halt()
	for hardware that was flakey 15-years ago.  Today we have
	"idle=poll" that removed HLT from idle, and so if such a machine
	is still running the upstream kernel, "idle=poll" is likely sufficient.
Who:	Len Brown <len.brown@intel.com>

----------------------------

What:	x86 "idle=mwait" cmdline param
When:	2012
Why:	simplify x86 idle code
Who:	Len Brown <len.brown@intel.com>

----------------------------

What:	PRISM54
When:	2.6.34

Why:	prism54 FullMAC PCI / Cardbus devices used to be supported only by the
	prism54 wireless driver. After Intersil stopped selling these
	devices in preference for the newer more flexible SoftMAC devices
	a SoftMAC device driver was required and prism54 did not support
	them. The p54pci driver now exists and has been present in the kernel for
	a while. This driver supports both SoftMAC devices and FullMAC devices.
	The main difference between these devices was the amount of memory which
	could be used for the firmware. The SoftMAC devices support a smaller
	amount of memory. Because of this the SoftMAC firmware fits into FullMAC
	devices's memory. p54pci supports not only PCI / Cardbus but also USB
	and SPI. Since p54pci supports all devices prism54 supports
	you will have a conflict. I'm not quite sure how distributions are
	handling this conflict right now. prism54 was kept around due to
	claims users may experience issues when using the SoftMAC driver.
	Time has passed users have not reported issues. If you use prism54
	and for whatever reason you cannot use p54pci please let us know!
	E-mail us at: linux-wireless@vger.kernel.org

	For more information see the p54 wiki page:

	http://wireless.kernel.org/en/users/Drivers/p54

Who:	Luis R. Rodriguez <lrodriguez@atheros.com>

---------------------------

What:	The ieee80211_regdom module parameter
When:	March 2010 / desktop catchup

Why:	This was inherited by the CONFIG_WIRELESS_OLD_REGULATORY code,
	and currently serves as an option for users to define an
	ISO / IEC 3166 alpha2 code for the country they are currently
	present in. Although there are userspace API replacements for this
	through nl80211 distributions haven't yet caught up with implementing
	decent alternatives through standard GUIs. Although available as an
	option through iw or wpa_supplicant its just a matter of time before
	distributions pick up good GUI options for this. The ideal solution
	would actually consist of intelligent designs which would do this for
	the user automatically even when travelling through different countries.
	Until then we leave this module parameter as a compromise.

	When userspace improves with reasonable widely-available alternatives for
	this we will no longer need this module parameter. This entry hopes that
	by the super-futuristically looking date of "March 2010" we will have
	such replacements widely available.

Who:	Luis R. Rodriguez <lrodriguez@atheros.com>

---------------------------

What:	dev->power.power_state
When:	July 2007
Why:	Broken design for runtime control over driver power states, confusing
	driver-internal runtime power management with:  mechanisms to support
	system-wide sleep state transitions; event codes that distinguish
	different phases of swsusp "sleep" transitions; and userspace policy
	inputs.  This framework was never widely used, and most attempts to
	use it were broken.  Drivers should instead be exposing domain-specific
	interfaces either to kernel or to userspace.
Who:	Pavel Machek <pavel@ucw.cz>

---------------------------

What:	/proc/<pid>/oom_adj
When:	August 2012
Why:	/proc/<pid>/oom_adj allows userspace to influence the oom killer's
	badness heuristic used to determine which task to kill when the kernel
	is out of memory.

	The badness heuristic has since been rewritten since the introduction of
	this tunable such that its meaning is deprecated.  The value was
	implemented as a bitshift on a score generated by the badness()
	function that did not have any precise units of measure.  With the
	rewrite, the score is given as a proportion of available memory to the
	task allocating pages, so using a bitshift which grows the score
	exponentially is, thus, impossible to tune with fine granularity.

	A much more powerful interface, /proc/<pid>/oom_score_adj, was
	introduced with the oom killer rewrite that allows users to increase or
	decrease the badness score linearly.  This interface will replace
	/proc/<pid>/oom_adj.

	A warning will be emitted to the kernel log if an application uses this
	deprecated interface.  After it is printed once, future warnings will be
	suppressed until the kernel is rebooted.

---------------------------

What:	remove EXPORT_SYMBOL(kernel_thread)
When:	August 2006
Files:	arch/*/kernel/*_ksyms.c
Check:	kernel_thread
Why:	kernel_thread is a low-level implementation detail.  Drivers should
        use the <linux/kthread.h> API instead which shields them from
	implementation details and provides a higherlevel interface that
	prevents bugs and code duplication
Who:	Christoph Hellwig <hch@lst.de>

---------------------------

What:	Unused EXPORT_SYMBOL/EXPORT_SYMBOL_GPL exports
	(temporary transition config option provided until then)
	The transition config option will also be removed at the same time.
When:	before 2.6.19
Why:	Unused symbols are both increasing the size of the kernel binary
	and are often a sign of "wrong API"
Who:	Arjan van de Ven <arjan@linux.intel.com>

---------------------------

What:	PHYSDEVPATH, PHYSDEVBUS, PHYSDEVDRIVER in the uevent environment
When:	October 2008
Why:	The stacking of class devices makes these values misleading and
	inconsistent.
	Class devices should not carry any of these properties, and bus
	devices have SUBSYTEM and DRIVER as a replacement.
Who:	Kay Sievers <kay.sievers@suse.de>

---------------------------

What:	ACPI procfs interface
When:	July 2008
Why:	ACPI sysfs conversion should be finished by January 2008.
	ACPI procfs interface will be removed in July 2008 so that
	there is enough time for the user space to catch up.
Who:	Zhang Rui <rui.zhang@intel.com>

---------------------------

What:	CONFIG_ACPI_PROCFS_POWER
When:	2.6.39
Why:	sysfs I/F for ACPI power devices, including AC and Battery,
        has been working in upstream kernel since 2.6.24, Sep 2007.
	In 2.6.37, we make the sysfs I/F always built in and this option
	disabled by default.
	Remove this option and the ACPI power procfs interface in 2.6.39.
Who:	Zhang Rui <rui.zhang@intel.com>

---------------------------

What:	/proc/acpi/event
When:	February 2008
Why:	/proc/acpi/event has been replaced by events via the input layer
	and netlink since 2.6.23.
Who:	Len Brown <len.brown@intel.com>

---------------------------

What:	i386/x86_64 bzImage symlinks
When:	April 2010

Why:	The i386/x86_64 merge provides a symlink to the old bzImage
	location so not yet updated user space tools, e.g. package
	scripts, do not break.
Who:	Thomas Gleixner <tglx@linutronix.de>

---------------------------

What:	GPIO autorequest on gpio_direction_{input,output}() in gpiolib
When:	February 2010
Why:	All callers should use explicit gpio_request()/gpio_free().
	The autorequest mechanism in gpiolib was provided mostly as a
	migration aid for legacy GPIO interfaces (for SOC based GPIOs).
	Those users have now largely migrated.  Platforms implementing
	the GPIO interfaces without using gpiolib will see no changes.
Who:	David Brownell <dbrownell@users.sourceforge.net>
---------------------------

What:	b43 support for firmware revision < 410
When:	The schedule was July 2008, but it was decided that we are going to keep the
        code as long as there are no major maintanance headaches.
	So it _could_ be removed _any_ time now, if it conflicts with something new.
Why:	The support code for the old firmware hurts code readability/maintainability
	and slightly hurts runtime performance. Bugfixes for the old firmware
	are not provided by Broadcom anymore.
Who:	Michael Buesch <m@bues.ch>

---------------------------

What:	Ability for non root users to shm_get hugetlb pages based on mlock
	resource limits
When:	2.6.31
Why:	Non root users need to be part of /proc/sys/vm/hugetlb_shm_group or
	have CAP_IPC_LOCK to be able to allocate shm segments backed by
	huge pages.  The mlock based rlimit check to allow shm hugetlb is
	inconsistent with mmap based allocations.  Hence it is being
	deprecated.
Who:	Ravikiran Thirumalai <kiran@scalex86.org>

---------------------------

What:	sysfs ui for changing p4-clockmod parameters
When:	September 2009
Why:	See commits 129f8ae9b1b5be94517da76009ea956e89104ce8 and
	e088e4c9cdb618675874becb91b2fd581ee707e6.
	Removal is subject to fixing any remaining bugs in ACPI which may
	cause the thermal throttling not to happen at the right time.
Who:	Dave Jones <davej@redhat.com>, Matthew Garrett <mjg@redhat.com>

-----------------------------

What:	fakephp and associated sysfs files in /sys/bus/pci/slots/
When:	2011
Why:	In 2.6.27, the semantics of /sys/bus/pci/slots was redefined to
	represent a machine's physical PCI slots. The change in semantics
	had userspace implications, as the hotplug core no longer allowed
	drivers to create multiple sysfs files per physical slot (required
	for multi-function devices, e.g.). fakephp was seen as a developer's
	tool only, and its interface changed. Too late, we learned that
	there were some users of the fakephp interface.

	In 2.6.30, the original fakephp interface was restored. At the same
	time, the PCI core gained the ability that fakephp provided, namely
	function-level hot-remove and hot-add.

	Since the PCI core now provides the same functionality, exposed in:

		/sys/bus/pci/rescan
		/sys/bus/pci/devices/.../remove
		/sys/bus/pci/devices/.../rescan

	there is no functional reason to maintain fakephp as well.

	We will keep the existing module so that 'modprobe fakephp' will
	present the old /sys/bus/pci/slots/... interface for compatibility,
	but users are urged to migrate their applications to the API above.

	After a reasonable transition period, we will remove the legacy
	fakephp interface.
Who:	Alex Chiang <achiang@hp.com>

---------------------------

What:	CONFIG_RFKILL_INPUT
When:	2.6.33
Why:	Should be implemented in userspace, policy daemon.
Who:	Johannes Berg <johannes@sipsolutions.net>

----------------------------

What:	sound-slot/service-* module aliases and related clutters in
	sound/sound_core.c
When:	August 2010
Why:	OSS sound_core grabs all legacy minors (0-255) of SOUND_MAJOR
	(14) and requests modules using custom sound-slot/service-*
	module aliases.  The only benefit of doing this is allowing
	use of custom module aliases which might as well be considered
	a bug at this point.  This preemptive claiming prevents
	alternative OSS implementations.

	Till the feature is removed, the kernel will be requesting
	both sound-slot/service-* and the standard char-major-* module
	aliases and allow turning off the pre-claiming selectively via
	CONFIG_SOUND_OSS_CORE_PRECLAIM and soundcore.preclaim_oss
	kernel parameter.

	After the transition phase is complete, both the custom module
	aliases and switches to disable it will go away.  This removal
	will also allow making ALSA OSS emulation independent of
	sound_core.  The dependency will be broken then too.
Who:	Tejun Heo <tj@kernel.org>

----------------------------

What:	sysfs-class-rfkill state file
When:	Feb 2014
Files:	net/rfkill/core.c
Why: 	Documented as obsolete since Feb 2010. This file is limited to 3
	states while the rfkill drivers can have 4 states.
Who: 	anybody or Florian Mickler <florian@mickler.org>

----------------------------

What: 	sysfs-class-rfkill claim file
When:	Feb 2012
Files:	net/rfkill/core.c
Why:	It is not possible to claim an rfkill driver since 2007. This is
	Documented as obsolete since Feb 2010.
Who: 	anybody or Florian Mickler <florian@mickler.org>

----------------------------

What:	iwlwifi 50XX module parameters
When:	3.0
Why:	The "..50" modules parameters were used to configure 5000 series and
	up devices; different set of module parameters also available for 4965
	with same functionalities. Consolidate both set into single place
	in drivers/net/wireless/iwlwifi/iwl-agn.c

Who:	Wey-Yi Guy <wey-yi.w.guy@intel.com>

----------------------------

What:	iwl4965 alias support
When:	3.0
Why:	Internal alias support has been present in module-init-tools for some
	time, the MODULE_ALIAS("iwl4965") boilerplate aliases can be removed
	with no impact.

Who:	Wey-Yi Guy <wey-yi.w.guy@intel.com>

---------------------------

What:	xt_NOTRACK
Files:	net/netfilter/xt_NOTRACK.c
When:	April 2011
Why:	Superseded by xt_CT
Who:	Netfilter developer team <netfilter-devel@vger.kernel.org>

----------------------------

What:	IRQF_DISABLED
When:	2.6.36
Why:	The flag is a NOOP as we run interrupt handlers with interrupts disabled
Who:	Thomas Gleixner <tglx@linutronix.de>

----------------------------

What: 	PCI DMA unmap state API
When:	August 2012
Why:	PCI DMA unmap state API (include/linux/pci-dma.h) was replaced
	with DMA unmap state API (DMA unmap state API can be used for
	any bus).
Who:	FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

----------------------------

What:	iwlwifi disable_hw_scan module parameters
When:	3.0
Why:	Hareware scan is the prefer method for iwlwifi devices for
	scanning operation. Remove software scan support for all the
	iwlwifi devices.

Who:	Wey-Yi Guy <wey-yi.w.guy@intel.com>

----------------------------

What:	Legacy, non-standard chassis intrusion detection interface.
When:	June 2011
Why:	The adm9240, w83792d and w83793 hardware monitoring drivers have
	legacy interfaces for chassis intrusion detection. A standard
	interface has been added to each driver, so the legacy interface
	can be removed.
Who:	Jean Delvare <khali@linux-fr.org>

----------------------------

What:	i2c_driver.attach_adapter
	i2c_driver.detach_adapter
When:	September 2011
Why:	These legacy callbacks should no longer be used as i2c-core offers
	a variety of preferable alternative ways to instantiate I2C devices.
Who:	Jean Delvare <khali@linux-fr.org>

----------------------------

What:	Opening a radio device node will no longer automatically switch the
	tuner mode from tv to radio.
When:	3.3
Why:	Just opening a V4L device should not change the state of the hardware
	like that. It's very unexpected and against the V4L spec. Instead, you
	switch to radio mode by calling VIDIOC_S_FREQUENCY. This is the second
	and last step of the move to consistent handling of tv and radio tuners.
Who:	Hans Verkuil <hans.verkuil@cisco.com>

----------------------------

What:	CONFIG_CFG80211_WEXT
When:	as soon as distributions ship new wireless tools, ie. wpa_supplicant 1.0
	and NetworkManager/connman/etc. that are able to use nl80211
Why:	Wireless extensions are deprecated, and userland tools are moving to
	using nl80211. New drivers are no longer using wireless extensions,
	and while there might still be old drivers, both new drivers and new
	userland no longer needs them and they can't be used for an feature
	developed in the past couple of years. As such, compatibility with
	wireless extensions in new drivers will be removed.
Who:	Johannes Berg <johannes@sipsolutions.net>

----------------------------

What:	g_file_storage driver
When:	3.8
Why:	This driver has been superseded by g_mass_storage.
Who:	Alan Stern <stern@rowland.harvard.edu>

----------------------------

What:   threeg and interface sysfs files in /sys/devices/platform/acer-wmi
When:   2012
Why:    In 3.0, we can now autodetect internal 3G device and already have
	the threeg rfkill device. So, we plan to remove threeg sysfs support
	for it's no longer necessary.

	We also plan to remove interface sysfs file that exposed which ACPI-WMI
	interface that was used by acer-wmi driver. It will replaced by
	information log when acer-wmi initial.
Who:    Lee, Chun-Yi <jlee@novell.com>

---------------------------

What:	/sys/devices/platform/_UDC_/udc/_UDC_/is_dualspeed file and
	is_dualspeed line in /sys/devices/platform/ci13xxx_*/udc/device file.
When:	3.8
Why:	The is_dualspeed file is superseded by maximum_speed in the same
	directory and is_dualspeed line in device file is superseded by
	max_speed line in the same file.

	The maximum_speed/max_speed specifies maximum speed supported by UDC.
	To check if dualspeeed is supported, check if the value is >= 3.
	Various possible speeds are defined in <linux/usb/ch9.h>.
Who:	Michal Nazarewicz <mina86@mina86.com>

----------------------------

What:	The XFS nodelaylog mount option
When:	3.3
Why:	The delaylog mode that has been the default since 2.6.39 has proven
	stable, and the old code is in the way of additional improvements in
	the log code.
Who:	Christoph Hellwig <hch@lst.de>

----------------------------

What:	iwlagn alias support
When:	3.5
Why:	The iwlagn module has been renamed iwlwifi.  The alias will be around
	for backward compatibility for several cycles and then dropped.
Who:	Don Fry <donald.h.fry@intel.com>

----------------------------

What:	pci_scan_bus_parented()
When:	3.5
Why:	The pci_scan_bus_parented() interface creates a new root bus.  The
	bus is created with default resources (ioport_resource and
	iomem_resource) that are always wrong, so we rely on arch code to
	correct them later.  Callers of pci_scan_bus_parented() should
	convert to using pci_scan_root_bus() so they can supply a list of
	bus resources when the bus is created.
Who:	Bjorn Helgaas <bhelgaas@google.com>

----------------------------

What:	Low Performance USB Block driver ("CONFIG_BLK_DEV_UB")
When:	3.6
Why:	This driver provides support for USB storage devices like "USB
	sticks". As of now, it is deactivated in Debian, Fedora and
        Ubuntu. All current users can switch over to usb-storage
        (CONFIG_USB_STORAGE) which only drawback is the additional SCSI
        stack.
Who:	Sebastian Andrzej Siewior <sebastian@breakpoint.cc>

----------------------------

What:	get_robust_list syscall
When:	2013
Why:	There appear to be no production users of the get_robust_list syscall,
	and it runs the risk of leaking address locations, allowing the bypass
	of ASLR. It was only ever intended for debugging, so it should be
	removed.
Who:	Kees Cook <keescook@chromium.org>

----------------------------

What:	Removing the pn544 raw driver.
When:	3.6
Why:	With the introduction of the NFC HCI and SHDL kernel layers, pn544.c
	is being replaced by pn544_hci.c which is accessible through the netlink
	and socket NFC APIs. Moreover, pn544.c is outdated and does not seem to
	work properly with the latest Android stacks.
	Having 2 drivers for the same hardware is confusing and as such we
	should only keep the one following the kernel NFC APIs.
Who:	Samuel Ortiz <sameo@linux.intel.com>

----------------------------

What:	setitimer accepts user NULL pointer (value)
When:	3.6
Why:	setitimer is not returning -EFAULT if user pointer is NULL. This
	violates the spec.
Who:	Sasikantha Babu <sasikanth.v19@gmail.com>

----------------------------

What:	remove bogus DV presets V4L2_DV_1080I29_97, V4L2_DV_1080I30 and
	V4L2_DV_1080I25
When:	3.6
Why:	These HDTV formats do not exist and were added by a confused mind
	(that was me, to be precise...)
Who:	Hans Verkuil <hans.verkuil@cisco.com>

----------------------------

What:	V4L2_CID_HCENTER, V4L2_CID_VCENTER V4L2 controls
When:	3.7
Why:	The V4L2_CID_VCENTER, V4L2_CID_HCENTER controls have been deprecated
	for about 4 years and they are not used by any mainline driver.
	There are newer controls (V4L2_CID_PAN*, V4L2_CID_TILT*) that provide
	similar	functionality.
Who:	Sylwester Nawrocki <sylvester.nawrocki@gmail.com>

----------------------------

What:	cgroup option updates via remount
When:	March 2013
Why:	Remount currently allows changing bound subsystems and
	release_agent.  Rebinding is hardly useful as it only works
	when the hierarchy is empty and release_agent itself should be
	replaced with conventional fsnotify.

----------------------------

What:  xt_recent rev 0
When:  2013
Who:   Pablo Neira Ayuso <pablo@netfilter.org>
Files: net/netfilter/xt_recent.c

----------------------------

What:	KVM debugfs statistics
When:	2013
Why:	KVM tracepoints provide mostly equivalent information in a much more
        flexible fashion.

----------------------------

What:	at91-mci driver ("CONFIG_MMC_AT91")
When:	3.7
Why:	There are two mci drivers: at91-mci and atmel-mci. The PDC support
	was added to atmel-mci as a first step to support more chips.
	Then at91-mci was kept only for old IP versions (on at91rm9200 and
	at91sam9261). The support of these IP versions has just been added
	to atmel-mci, so atmel-mci can be used for all chips.
Who:	Ludovic Desroches <ludovic.desroches@atmel.com>

----------------------------

What:	net/wanrouter/
When:	June 2013
Why:	Unsupported/unmaintained/unused since 2.6

----------------------------

What:	V4L2 selections API target rectangle and flags unification, the
	following definitions will be removed: V4L2_SEL_TGT_CROP_ACTIVE,
	V4L2_SEL_TGT_COMPOSE_ACTIVE, V4L2_SUBDEV_SEL_*, V4L2_SUBDEV_SEL_FLAG_*
	in favor of common V4L2_SEL_TGT_* and V4L2_SEL_FLAG_* definitions.
	For more details see include/linux/v4l2-common.h.
When:	3.8
Why:	The regular V4L2 selections and the subdev selection API originally
	defined distinct names for the target rectangles and flags - V4L2_SEL_*
	and V4L2_SUBDEV_SEL_*. Although, it turned out that the meaning of these
	target rectangles is virtually identical and the APIs were consolidated
	to use single set of names - V4L2_SEL_*. This didn't involve any ABI
	changes. Alias definitions were created for the original ones to avoid
	any instabilities in the user space interface. After few cycles these
	backward compatibility definitions will be removed.
Who:	Sylwester Nawrocki <sylvester.nawrocki@gmail.com>

----------------------------

What:	Using V4L2_CAP_VIDEO_CAPTURE and V4L2_CAP_VIDEO_OUTPUT flags
	to indicate a V4L2 memory-to-memory device capability
When:	3.8
Why:	New drivers should use new V4L2_CAP_VIDEO_M2M capability flag
	to indicate a V4L2 video memory-to-memory (M2M) device and
	applications can now identify a M2M video device by checking
	for V4L2_CAP_VIDEO_M2M, with VIDIOC_QUERYCAP ioctl. Using ORed
	V4L2_CAP_VIDEO_CAPTURE and V4L2_CAP_VIDEO_OUTPUT flags for M2M
	devices is ambiguous and may lead, for example, to identifying
	a M2M device as a video	capture or output device.
Who:	Sylwester Nawrocki <s.nawrocki@samsung.com>

----------------------------