x86 idle: deprecate mwait_idle() and "idle=mwait" cmdline param

[pandora-kernel.git] / 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.

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

What:   x86 floppy disable_hlt
When:   2012
Why:    ancient workaround of dubious utility clutters the
        code used by everybody else.
Who:    Len Brown <len.brown@intel.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:   IRQF_SAMPLE_RANDOM
Check:  IRQF_SAMPLE_RANDOM
When:   July 2009

Why:    Many of IRQF_SAMPLE_RANDOM users are technically bogus as entropy
        sources in the kernel's current entropy model. To resolve this, every
        input point to the kernel's entropy pool needs to better document the
        type of entropy source it actually is. This will be replaced with
        additional add_*_randomness functions in drivers/char/random.c

Who:    Robin Getz <rgetz@blackfin.uclinux.org> & Matt Mackall <mpm@selenic.com>

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

What:   Deprecated snapshot ioctls
When:   2.6.36

Why:    The ioctls in kernel/power/user.c were marked as deprecated long time
        ago. Now they notify users about that so that they need to replace
        their userspace. After some more time, remove them completely.

Who:    Jiri Slaby <jirislaby@gmail.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:   Video4Linux obsolete drivers using V4L1 API
When:   kernel 2.6.39
Files:  drivers/staging/se401/* drivers/staging/usbvideo/*
Check:  drivers/staging/se401/se401.c drivers/staging/usbvideo/usbvideo.c
Why:    There are some drivers still using V4L1 API, despite all efforts we've done
        to migrate. Those drivers are for obsolete hardware that the old maintainer
        didn't care (or not have the hardware anymore), and that no other developer
        could find any hardware to buy. They probably have no practical usage today,
        and people with such old hardware could probably keep using an older version
        of the kernel. Those drivers will be moved to staging on 2.6.38 and, if nobody
        cares enough to port and test them with V4L2 API, they'll be removed on 2.6.39.
Who:    Mauro Carvalho Chehab <mchehab@infradead.org>

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

What:   Video4Linux: Remove obsolete ioctl's
When:   kernel 2.6.39
Files:  include/media/videodev2.h
Why:    Some ioctl's were defined wrong on 2.6.2 and 2.6.6, using the wrong
        type of R/W arguments. They were fixed, but the old ioctl names are
        still there, maintained to avoid breaking binary compatibility:
          #define VIDIOC_OVERLAY_OLD    _IOWR('V', 14, int)
          #define VIDIOC_S_PARM_OLD     _IOW('V', 22, struct v4l2_streamparm)
          #define VIDIOC_S_CTRL_OLD     _IOW('V', 28, struct v4l2_control)
          #define VIDIOC_G_AUDIO_OLD    _IOWR('V', 33, struct v4l2_audio)
          #define VIDIOC_G_AUDOUT_OLD   _IOWR('V', 49, struct v4l2_audioout)
          #define VIDIOC_CROPCAP_OLD    _IOR('V', 58, struct v4l2_cropcap)
        There's no sense on preserving those forever, as it is very doubtful
        that someone would try to use a such old binary with a modern kernel.
        Removing them will allow us to remove some magic done at the V4L ioctl
        handler.

Who:    Mauro Carvalho Chehab <mchehab@infradead.org>

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

What:   sys_sysctl
When:   September 2010
Option: CONFIG_SYSCTL_SYSCALL
Why:    The same information is available in a more convenient from
        /proc/sys, and none of the sysctl variables appear to be
        important performance wise.

        Binary sysctls are a long standing source of subtle kernel
        bugs and security issues.

        When I looked several months ago all I could find after
        searching several distributions were 5 user space programs and
        glibc (which falls back to /proc/sys) using this syscall.

        The man page for sysctl(2) documents it as unusable for user
        space programs.

        sysctl(2) is not generally ABI compatible to a 32bit user
        space application on a 64bit and a 32bit kernel.

        For the last several months the policy has been no new binary
        sysctls and no one has put forward an argument to use them.

        Binary sysctls issues seem to keep happening appearing so
        properly deprecating them (with a warning to user space) and a
        2 year grace warning period will mean eventually we can kill
        them and end the pain.

        In the mean time individual binary sysctls can be dealt with
        in a piecewise fashion.

Who:    Eric Biederman <ebiederm@xmission.com>

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

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:   CS5535/CS5536 obsolete GPIO driver
When:   June 2011
Files:  drivers/staging/cs5535_gpio/*
Check:  drivers/staging/cs5535_gpio/cs5535_gpio.c
Why:    A newer driver replaces this; it is drivers/gpio/cs5535-gpio.c, and
        integrates with the Linux GPIO subsystem.  The old driver has been
        moved to staging, and will be removed altogether around 2.6.40.
        Please test the new driver, and ensure that the functionality you
        need and any bugfixes from the old driver are available in the new
        one.
Who:    Andres Salomon <dilinger@queued.net>

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

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 kenrel 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/button
When:   August 2007
Why:    /proc/acpi/button has been replaced by events to the input layer
        since 2.6.20.
Who:    Len Brown <len.brown@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 <mb@bu3sch.de>

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

What:   /sys/o2cb symlink
When:   January 2010
Why:    /sys/fs/o2cb is the proper location for this information - /sys/o2cb
        exists as a symlink for backwards compatibility for old versions of
        ocfs2-tools. 2 years should be sufficient time to phase in new versions
        which know to look in /sys/fs/o2cb.
Who:    ocfs2-devel@oss.oracle.com

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

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:   CONFIG_THERMAL_HWMON
When:   January 2009
Why:    This option was introduced just to allow older lm-sensors userspace
        to keep working over the upgrade to 2.6.26. At the scheduled time of
        removal fixed lm-sensors (2.x or 3.x) should be readily available.
Who:    Rene Herman <rene.herman@gmail.com>

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

What:   Code that is now under CONFIG_WIRELESS_EXT_SYSFS
        (in net/core/net-sysfs.c)
When:   After the only user (hal) has seen a release with the patches
        for enough time, probably some time in 2010.
Why:    Over 1K .text/.data size reduction, data is available in other
        ways (ioctls)
Who:    Johannes Berg <johannes@sipsolutions.net>

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

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:   Support for lcd_switch and display_get in asus-laptop driver
When:   March 2010
Why:    These two features use non-standard interfaces. There are the
        only features that really need multiple path to guess what's
        the right method name on a specific laptop.

        Removing them will allow to remove a lot of code an significantly
        clean the drivers.

        This will affect the backlight code which won't be able to know
        if the backlight is on or off. The platform display file will also be
        write only (like the one in eeepc-laptop).

        This should'nt affect a lot of user because they usually know
        when their display is on or off.

Who:    Corentin Chary <corentin.chary@gmail.com>

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

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:   capifs
When:   February 2011
Files:  drivers/isdn/capi/capifs.*
Why:    udev fully replaces this special file system that only contains CAPI
        NCCI TTY device nodes. User space (pppdcapiplugin) works without
        noticing the difference.
Who:    Jan Kiszka <jan.kiszka@web.de>

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

What:   KVM paravirt mmu host support
When:   January 2011
Why:    The paravirt mmu host support is slower than non-paravirt mmu, both
        on newer and older hardware.  It is already not exposed to the guest,
        and kept only for live migration purposes.
Who:    Avi Kivity <avi@redhat.com>

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

What:   iwlwifi 50XX module parameters
When:   2.6.40
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:   2.6.40
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:   The acpi_sleep=s4_nonvs command line option
When:   2.6.37
Files:  arch/x86/kernel/acpi/sleep.c
Why:    superseded by acpi_sleep=nonvs
Who:    Rafael J. Wysocki <rjw@sisk.pl>

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

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:   DMA_xxBIT_MASK macros
When:   Jun 2011
Why:    DMA_xxBIT_MASK macros were replaced with DMA_BIT_MASK() macros.
Who:    FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

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

What:   namespace cgroup (ns_cgroup)
When:   2.6.38
Why:    The ns_cgroup leads to some problems:
        * cgroup creation is out-of-control
        * cgroup name can conflict when pids are looping
        * it is not possible to have a single process handling
        a lot of namespaces without falling in a exponential creation time
        * we may want to create a namespace without creating a cgroup

        The ns_cgroup is replaced by a compatibility flag 'clone_children',
        where a newly created cgroup will copy the parent cgroup values.
        The userspace has to manually create a cgroup and add a task to
        the 'tasks' file.
Who:    Daniel Lezcano <daniel.lezcano@free.fr>

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

What:   iwlwifi disable_hw_scan module parameters
When:   2.6.40
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:   access to nfsd auth cache through sys_nfsservctl or '.' files
        in the 'nfsd' filesystem.
When:   2.6.40
Why:    This is a legacy interface which have been replaced by a more
        dynamic cache.  Continuing to maintain this interface is an
        unnecessary burden.
Who:    NeilBrown <neilb@suse.de>

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

What:   i2c_adapter.id
When:   June 2011
Why:    This field is deprecated. I2C device drivers shouldn't change their
        behavior based on the underlying I2C adapter. Instead, the I2C
        adapter driver should instantiate the I2C devices and provide the
        needed platform-specific information.
Who:    Jean Delvare <khali@linux-fr.org>

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

What:   cancel_rearming_delayed_work[queue]()
When:   2.6.39

Why:    The functions have been superceded by cancel_delayed_work_sync()
        quite some time ago.  The conversion is trivial and there is no
        in-kernel user left.
Who:    Tejun Heo <tj@kernel.org>

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

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:   noswapaccount kernel command line parameter
When:   2.6.40
Why:    The original implementation of memsw feature enabled by
        CONFIG_CGROUP_MEM_RES_CTLR_SWAP could be disabled by the noswapaccount
        kernel parameter (introduced in 2.6.29-rc1). Later on, this decision
        turned out to be not ideal because we cannot have the feature compiled
        in and disabled by default and let only interested to enable it
        (e.g. general distribution kernels might need it). Therefore we have
        added swapaccount[=0|1] parameter (introduced in 2.6.37) which provides
        the both possibilities. If we remove noswapaccount we will have
        less command line parameters with the same functionality and we
        can also cleanup the parameter handling a bit ().
Who:    Michal Hocko <mhocko@suse.cz>

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