19 Oct, 2011
1 commit
-
To support >32-bit physical addresses for UIO_MEM_PHYS type we need to
extend the width of 'addr' in struct uio_mem. Numerous platforms like
embedded PPC, ARM, and X86 have support for systems with larger physical
address than logical.Since 'addr' may contain a physical, logical, or virtual address the
easiest solution is to just change the type to 'phys_addr_t' which
should always be greater than or equal to the sizeof(void *) such that
it can properly hold any of the address types.For physical address we can support up to a 44-bit physical address on a
typical 32-bit system as we utilize remap_pfn_range() for the mapping of
the memory region and pfn's are represnted by shifting the address by
the page size (typically 4k).Signed-off-by: Kai Jiang
Signed-off-by: Minghuan Lian
Signed-off-by: Kumar Gala
Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman
23 Aug, 2011
1 commit
-
Remove one *goto* label in uio.c.
Signed-off-by: Wanlong Gao
Signed-off-by: "Hans J. Koch"
Signed-off-by: Greg Kroah-Hartman
20 Apr, 2011
2 commits
-
The number of uio devices that could be used should be less than
UIO_MAX_DEVICES by design, and this work guards any cases in which id
more than UIO_MAX_DEVICES is utilized.Signed-off-by: Hillf Danton
Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman -
When finding mm index for vma it looks more flexible that the mm could
be sparse, and both the size of mm and the pgoff of vma could give
correct selection.Signed-off-by: Hillf Danton
Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman
11 Nov, 2010
1 commit
-
My old mail address doesn't exist anymore. This changes all occurrences
to my new address.Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman
23 Oct, 2010
6 commits
-
* git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core-2.6: (31 commits)
driver core: Display error codes when class suspend fails
Driver core: Add section count to memory_block struct
Driver core: Add mutex for adding/removing memory blocks
Driver core: Move find_memory_block routine
hpilo: Despecificate driver from iLO generation
driver core: Convert link_mem_sections to use find_memory_block_hinted.
driver core: Introduce find_memory_block_hinted which utilizes kset_find_obj_hinted.
kobject: Introduce kset_find_obj_hinted.
driver core: fix build for CONFIG_BLOCK not enabled
driver-core: base: change to new flag variable
sysfs: only access bin file vm_ops with the active lock
sysfs: Fail bin file mmap if vma close is implemented.
FW_LOADER: fix kconfig dependency warning on HOTPLUG
uio: Statically allocate uio_class and use class .dev_attrs.
uio: Support 2^MINOR_BITS minors
uio: Cleanup irq handling.
uio: Don't clear driver data
uio: Fix lack of locking in init_uio_class
SYSFS: Allow boot time switching between deprecated and modern sysfs layout
driver core: remove CONFIG_SYSFS_DEPRECATED_V2 but keep it for block devices
... -
Instead of adding uio class attributes manually after the uio device has
been created and we have sent a uevent to userspace, use the class
attribute mechanism. This removes races and makes the code simpler.At the same time don't bother to dynamically allocate a struct class for
uio, just declare one statically. Less code is needed and it is easier
to set the class parameters.tune the classSigned-off-by: Eric W. Biederman
Reviewed-by: Thomas Gleixner
Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman -
register_chrdev limits uio devices to 256 minor numbers which causes
problems on one system I have with 384+ uio devices. So instead set
UIO_MAX_DEVICES to the maximum number of minors and use
alloc_chrdev_region to reserve the uio minors.The final result is that the code works the same but the uio driver now
supports any minor the idr allocator comes up with.Signed-off-by: Eric W. Biederman
Reviewed-by: Thomas Gleixner
Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman -
Change the value of UIO_IRQ_NONE -2 to 0. 0 is well defined in the rest
of the kernel as the value to indicate an irq has not been assigned.Update the calls to request_irq and free_irq to only ignore UIO_IRQ_NONE
and UIO_IRQ_CUSTOM allowing the rest of the kernel's possible irq
numbers to be used.Signed-off-by: Eric W. Biederman
Reviewed-by: Thomas Gleixner
Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman -
Currently uio sets it's driver data to NULL just as it is unregistering
attributes. sysfs maks the guaranatee that it will not call attributes
after device_destroy is called so this is unncessary and leads to lots
of unnecessary code in uio.cSigned-off-by: Eric W. Biederman
Reviewed-by: Thomas Gleixner
Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman -
There is no locking in init_uio_class so multiple
drivers can race and create multiple uio classes.Fix this by simplifying the code. In particular always
register the uio class during module_init and make things
simpler.Signed-off-by: Eric W. Biederman
Reviewed-by: Thomas Gleixner
Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman
15 Oct, 2010
1 commit
-
All file_operations should get a .llseek operation so we can make
nonseekable_open the default for future file operations without a
.llseek pointer.The three cases that we can automatically detect are no_llseek, seq_lseek
and default_llseek. For cases where we can we can automatically prove that
the file offset is always ignored, we use noop_llseek, which maintains
the current behavior of not returning an error from a seek.New drivers should normally not use noop_llseek but instead use no_llseek
and call nonseekable_open at open time. Existing drivers can be converted
to do the same when the maintainer knows for certain that no user code
relies on calling seek on the device file.The generated code is often incorrectly indented and right now contains
comments that clarify for each added line why a specific variant was
chosen. In the version that gets submitted upstream, the comments will
be gone and I will manually fix the indentation, because there does not
seem to be a way to do that using coccinelle.Some amount of new code is currently sitting in linux-next that should get
the same modifications, which I will do at the end of the merge window.Many thanks to Julia Lawall for helping me learn to write a semantic
patch that does all this.===== begin semantic patch =====
// This adds an llseek= method to all file operations,
// as a preparation for making no_llseek the default.
//
// The rules are
// - use no_llseek explicitly if we do nonseekable_open
// - use seq_lseek for sequential files
// - use default_llseek if we know we access f_pos
// - use noop_llseek if we know we don't access f_pos,
// but we still want to allow users to call lseek
//
@ open1 exists @
identifier nested_open;
@@
nested_open(...)
{}
@ open exists@
identifier open_f;
identifier i, f;
identifier open1.nested_open;
@@
int open_f(struct inode *i, struct file *f)
{}
@ read disable optional_qualifier exists @
identifier read_f;
identifier f, p, s, off;
type ssize_t, size_t, loff_t;
expression E;
identifier func;
@@
ssize_t read_f(struct file *f, char *p, size_t s, loff_t *off)
{}
@ read_no_fpos disable optional_qualifier exists @
identifier read_f;
identifier f, p, s, off;
type ssize_t, size_t, loff_t;
@@
ssize_t read_f(struct file *f, char *p, size_t s, loff_t *off)
{
... when != off
}@ write @
identifier write_f;
identifier f, p, s, off;
type ssize_t, size_t, loff_t;
expression E;
identifier func;
@@
ssize_t write_f(struct file *f, const char *p, size_t s, loff_t *off)
{}
@ write_no_fpos @
identifier write_f;
identifier f, p, s, off;
type ssize_t, size_t, loff_t;
@@
ssize_t write_f(struct file *f, const char *p, size_t s, loff_t *off)
{
... when != off
}@ fops0 @
identifier fops;
@@
struct file_operations fops = {
...
};@ has_llseek depends on fops0 @
identifier fops0.fops;
identifier llseek_f;
@@
struct file_operations fops = {
...
.llseek = llseek_f,
...
};@ has_read depends on fops0 @
identifier fops0.fops;
identifier read_f;
@@
struct file_operations fops = {
...
.read = read_f,
...
};@ has_write depends on fops0 @
identifier fops0.fops;
identifier write_f;
@@
struct file_operations fops = {
...
.write = write_f,
...
};@ has_open depends on fops0 @
identifier fops0.fops;
identifier open_f;
@@
struct file_operations fops = {
...
.open = open_f,
...
};// use no_llseek if we call nonseekable_open
////////////////////////////////////////////
@ nonseekable1 depends on !has_llseek && has_open @
identifier fops0.fops;
identifier nso ~= "nonseekable_open";
@@
struct file_operations fops = {
... .open = nso, ...
+.llseek = no_llseek, /* nonseekable */
};@ nonseekable2 depends on !has_llseek @
identifier fops0.fops;
identifier open.open_f;
@@
struct file_operations fops = {
... .open = open_f, ...
+.llseek = no_llseek, /* open uses nonseekable */
};// use seq_lseek for sequential files
/////////////////////////////////////
@ seq depends on !has_llseek @
identifier fops0.fops;
identifier sr ~= "seq_read";
@@
struct file_operations fops = {
... .read = sr, ...
+.llseek = seq_lseek, /* we have seq_read */
};// use default_llseek if there is a readdir
///////////////////////////////////////////
@ fops1 depends on !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier readdir_e;
@@
// any other fop is used that changes pos
struct file_operations fops = {
... .readdir = readdir_e, ...
+.llseek = default_llseek, /* readdir is present */
};// use default_llseek if at least one of read/write touches f_pos
/////////////////////////////////////////////////////////////////
@ fops2 depends on !fops1 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier read.read_f;
@@
// read fops use offset
struct file_operations fops = {
... .read = read_f, ...
+.llseek = default_llseek, /* read accesses f_pos */
};@ fops3 depends on !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier write.write_f;
@@
// write fops use offset
struct file_operations fops = {
... .write = write_f, ...
+ .llseek = default_llseek, /* write accesses f_pos */
};// Use noop_llseek if neither read nor write accesses f_pos
///////////////////////////////////////////////////////////@ fops4 depends on !fops1 && !fops2 && !fops3 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier read_no_fpos.read_f;
identifier write_no_fpos.write_f;
@@
// write fops use offset
struct file_operations fops = {
...
.write = write_f,
.read = read_f,
...
+.llseek = noop_llseek, /* read and write both use no f_pos */
};@ depends on has_write && !has_read && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier write_no_fpos.write_f;
@@
struct file_operations fops = {
... .write = write_f, ...
+.llseek = noop_llseek, /* write uses no f_pos */
};@ depends on has_read && !has_write && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
identifier read_no_fpos.read_f;
@@
struct file_operations fops = {
... .read = read_f, ...
+.llseek = noop_llseek, /* read uses no f_pos */
};@ depends on !has_read && !has_write && !fops1 && !fops2 && !has_llseek && !nonseekable1 && !nonseekable2 && !seq @
identifier fops0.fops;
@@
struct file_operations fops = {
...
+.llseek = noop_llseek, /* no read or write fn */
};
===== End semantic patch =====Signed-off-by: Arnd Bergmann
Cc: Julia Lawall
Cc: Christoph Hellwig
30 Mar, 2010
1 commit
-
…it slab.h inclusion from percpu.h
percpu.h is included by sched.h and module.h and thus ends up being
included when building most .c files. percpu.h includes slab.h which
in turn includes gfp.h making everything defined by the two files
universally available and complicating inclusion dependencies.percpu.h -> slab.h dependency is about to be removed. Prepare for
this change by updating users of gfp and slab facilities include those
headers directly instead of assuming availability. As this conversion
needs to touch large number of source files, the following script is
used as the basis of conversion.http://userweb.kernel.org/~tj/misc/slabh-sweep.py
The script does the followings.
* Scan files for gfp and slab usages and update includes such that
only the necessary includes are there. ie. if only gfp is used,
gfp.h, if slab is used, slab.h.* When the script inserts a new include, it looks at the include
blocks and try to put the new include such that its order conforms
to its surrounding. It's put in the include block which contains
core kernel includes, in the same order that the rest are ordered -
alphabetical, Christmas tree, rev-Xmas-tree or at the end if there
doesn't seem to be any matching order.* If the script can't find a place to put a new include (mostly
because the file doesn't have fitting include block), it prints out
an error message indicating which .h file needs to be added to the
file.The conversion was done in the following steps.
1. The initial automatic conversion of all .c files updated slightly
over 4000 files, deleting around 700 includes and adding ~480 gfp.h
and ~3000 slab.h inclusions. The script emitted errors for ~400
files.2. Each error was manually checked. Some didn't need the inclusion,
some needed manual addition while adding it to implementation .h or
embedding .c file was more appropriate for others. This step added
inclusions to around 150 files.3. The script was run again and the output was compared to the edits
from #2 to make sure no file was left behind.4. Several build tests were done and a couple of problems were fixed.
e.g. lib/decompress_*.c used malloc/free() wrappers around slab
APIs requiring slab.h to be added manually.5. The script was run on all .h files but without automatically
editing them as sprinkling gfp.h and slab.h inclusions around .h
files could easily lead to inclusion dependency hell. Most gfp.h
inclusion directives were ignored as stuff from gfp.h was usually
wildly available and often used in preprocessor macros. Each
slab.h inclusion directive was examined and added manually as
necessary.6. percpu.h was updated not to include slab.h.
7. Build test were done on the following configurations and failures
were fixed. CONFIG_GCOV_KERNEL was turned off for all tests (as my
distributed build env didn't work with gcov compiles) and a few
more options had to be turned off depending on archs to make things
build (like ipr on powerpc/64 which failed due to missing writeq).* x86 and x86_64 UP and SMP allmodconfig and a custom test config.
* powerpc and powerpc64 SMP allmodconfig
* sparc and sparc64 SMP allmodconfig
* ia64 SMP allmodconfig
* s390 SMP allmodconfig
* alpha SMP allmodconfig
* um on x86_64 SMP allmodconfig8. percpu.h modifications were reverted so that it could be applied as
a separate patch and serve as bisection point.Given the fact that I had only a couple of failures from tests on step
6, I'm fairly confident about the coverage of this conversion patch.
If there is a breakage, it's likely to be something in one of the arch
headers which should be easily discoverable easily on most builds of
the specific arch.Signed-off-by: Tejun Heo <tj@kernel.org>
Guess-its-ok-by: Christoph Lameter <cl@linux-foundation.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Lee Schermerhorn <Lee.Schermerhorn@hp.com>
08 Mar, 2010
1 commit
-
Constify struct sysfs_ops.
This is part of the ops structure constification
effort started by Arjan van de Ven et al.Benefits of this constification:
* prevents modification of data that is shared
(referenced) by many other structure instances
at runtime* detects/prevents accidental (but not intentional)
modification attempts on archs that enforce
read-only kernel data at runtime* potentially better optimized code as the compiler
can assume that the const data cannot be changed* the compiler/linker move const data into .rodata
and therefore exclude them from false sharingSigned-off-by: Emese Revfy
Acked-by: David Teigland
Acked-by: Matt Domsch
Acked-by: Maciej Sosnowski
Acked-by: Hans J. Koch
Acked-by: Pekka Enberg
Acked-by: Jens Axboe
Acked-by: Stephen Hemminger
Signed-off-by: Greg Kroah-Hartman
12 Oct, 2009
1 commit
-
After m68k's task_thread_info() doesn't refer to current,
it's possible to remove sched.h from interrupt.h and not break m68k!
Many thanks to Heiko Carstens for allowing this.Signed-off-by: Alexey Dobriyan
28 Sep, 2009
1 commit
-
* mark struct vm_area_struct::vm_ops as const
* mark vm_ops in AGP codeBut leave TTM code alone, something is fishy there with global vm_ops
being used.Signed-off-by: Alexey Dobriyan
Signed-off-by: Linus Torvalds
25 Mar, 2009
2 commits
-
If a UIO memory region does not start on a page boundary but straddles one,
the number of actual pages that overlap the memory region may be calculated
incorrectly because the offset isn't taken into account. If userspace sets
the mmap length to offset+size, it may fail with -EINVAL if UIO thinks it's
trying to allocate too many pages.Signed-off-by: Ian Abbott
Cc: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman -
If a UIO device has several memory mappings, it can be difficult for userspace
to find the right one. The situation becomes even worse if the UIO driver can
handle different versions of a card that have different numbers of mappings.
Benedikt Spranger has such cards and pointed this out to me. Thanks, Bene!To address this problem, this patch adds "name" sysfs attributes for each
mapping. Userspace can use these to clearly identify each mapping. The name
string is optional. If a driver doesn't set it, an empty string will be
returned, so this patch won't break existing drivers.The same problem exists for port region information, so a "name" attribute is
added there, too.Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman
07 Jan, 2009
1 commit
-
Devices sometimes have memory where all or parts of it can not be mapped to
userspace. But it might still be possible to access this memory from
userspace by other means. An example are PCI cards that advertise not only
mappable memory but also ioport ranges. On x86 architectures, these can be
accessed with ioperm, iopl, inb, outb, and friends. Mike Frysinger (CCed)
reported a similar problem on Blackfin arch where it doesn't seem to be easy
to mmap non-cached memory but it can still be accessed from userspace.This patch allows kernel drivers to pass information about such ports to
userspace. Similar to the existing mem[] array, it adds a port[] array to
struct uio_info. Each port range is described by start, size, and porttype.If a driver fills in at least one such port range, the UIO core will simply
pass this information to userspace by creating a new directory "portio"
underneath /sys/class/uio/uioN/. Similar to the "mem" directory, it will
contain a subdirectory (portX) for each port range given.Note that UIO simply passes this information to userspace, it performs no
action whatsoever with this data. It's userspace's responsibility to obtain
access to these ports and to solve arch dependent issues. The "porttype"
attribute tells userspace what kind of port it is dealing with.This mechanism could also be used to give userspace information about GPIOs
related to a device. You frequently find such hardware in embedded devices,
so I added a UIO_PORT_GPIO definition. I'm not really sure if this is a good
idea since there are other solutions to this problem, but it won't hurt much
anyway.Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman
02 Nov, 2008
1 commit
-
As it is, all instances of ->release() for files that have ->fasync()
need to remember to evict file from fasync lists; forgetting that
creates a hole and we actually have a bunch that *does* forget.So let's keep our lives simple - let __fput() check FASYNC in
file->f_flags and call ->fasync() there if it's been set. And lose that
crap in ->release() instances - leaving it there is still valid, but we
don't have to bother anymore.Signed-off-by: Al Viro
Signed-off-by: Linus Torvalds
21 Oct, 2008
1 commit
-
* 'bkl-removal' of git://git.lwn.net/linux-2.6:
UIO: BKL removal
17 Oct, 2008
4 commits
-
Fill in needed locking around idr accesses, then remove the big kernel lock
from the UIO driver. Since there are no in-tree UIO drivers with open()
methods, no further BKL pushdown is required.Acked-by: Hans J. Koch
Acked-by: Greg Kroah-Hartman
Signed-off-by: Jonathan Corbet -
mmap() doesn't work as expected for UIO_MEM_LOGICAL or UIO_MEM_VIRTUAL
mappings. The offset into the memory needs to be added, otherwise
uio_vma_fault always returns the first page only. Note that for UIO
userspace calls mmap() with offset = N * getpagesize() to access
mapping N. This must be compensated when calculating the offset. A
comment was added to explain this since it is not obvious.Signed-off-by: Andrew G. Harvey
Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman -
This patch adds an "offset" attribute for UIO mappings. It shows the
difference between the actual start address of the memory and the start
address of the page.Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman -
Now that device_create() has been audited, rename things back to the
original call to be sane.Signed-off-by: Greg Kroah-Hartman
22 Jul, 2008
1 commit
-
Sometimes it is necessary to enable/disable the interrupt of a UIO device
from the userspace part of the driver. With this patch, the UIO kernel driver
can implement an "irqcontrol()" function that does this. Userspace can write
an s32 value to /dev/uioX (usually 0 or 1 to turn the irq off or on). The
UIO core will then call the driver's irqcontrol function.Signed-off-by: Hans J. Koch
Acked-by: Uwe Kleine-König
Acked-by: Magnus Damm
Signed-off-by: Greg Kroah-Hartman
15 Jul, 2008
1 commit
21 Jun, 2008
1 commit
-
Signed-off-by: Jonathan Corbet
21 May, 2008
1 commit
-
There is a race from when a device is created with device_create() and
then the drvdata is set with a call to dev_set_drvdata() in which a
sysfs file could be open, yet the drvdata will be NULL, causing all
sorts of bad things to happen.This patch fixes the problem by using the new function,
device_create_drvdata().Cc: Kay Sievers
Cc: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman
20 Apr, 2008
1 commit
-
Otherwise the device might just disappear while /dev/uioX is being used
which results in an Oops.Signed-off-by: Uwe Kleine-König
Signed-off-by: Hans J Koch
Signed-off-by: Greg Kroah-Hartman
25 Mar, 2008
1 commit
-
Mapping of physical memory in UIO needs pgprot_noncached() to ensure
that IO memory is not cached. Without pgprot_noncached(), it (accidentally)
works on x86 and arm, but fails on PPC.Signed-off-by: Jean-Samuel Chenard
Signed-off-by: Hans J Koch
Cc: stable
Signed-off-by: Greg Kroah-Hartman
22 Feb, 2008
1 commit
-
This fixes two bugs with UIO that cropped up recently in -rc1
1) WARNING: at fs/sysfs/file.c:334 sysfs_open_file when trying to open
a map addr/size file - complaining about missing sysfs_ops for ktype2) Permission denied when reading uio/uio0/maps/map0/{addr,size} when
files are mode S_IRUGOAlso fix a typo: attr_attribute -> addr_attribute
Signed-off-by: Brandon Philips
Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman
07 Feb, 2008
1 commit
-
Convert uio from nopage to fault.
Signed-off-by: Nick Piggin
Acked-by: Hans J Koch
Signed-off-by: Andrew Morton
Signed-off-by: Linus Torvalds
25 Jan, 2008
6 commits
-
Signed-off-by: Jan Engelhardt
Signed-off-by: Greg Kroah-Hartman -
There is no need for kobject_unregister() anymore, thanks to Kay's
kobject cleanup changes, so replace all instances of it with
kobject_put().Cc: Kay Sievers
Signed-off-by: Greg Kroah-Hartman -
Now that the old kobject_init() function is gone, rename
kobject_init_ng() to kobject_init() to clean up the namespace.Cc: Kay Sievers
Signed-off-by: Greg Kroah-Hartman -
Now that the old kobject_add() function is gone, rename kobject_add_ng()
to kobject_add() to clean up the namespace.Cc: Kay Sievers
Signed-off-by: Greg Kroah-Hartman -
The uio kobject code is "wierd". This patch should hopefully fix it up
to be sane and not leak memory anymore.Cc: Kay Sievers
Cc: Thomas Gleixner
Cc: Benedikt Spranger
Signed-off-by: Hans J. Koch
Signed-off-by: Greg Kroah-Hartman -
We don't need a "default" ktype for a kset. We should set this
explicitly every time for each kset. This change is needed so that we
can make ksets dynamic, and cleans up one of the odd, undocumented
assumption that the kset/kobject/ktype model has.This patch is based on a lot of help from Kay Sievers.
Nasty bug in the block code was found by Dave Young
Cc: Kay Sievers
Cc: Dave Young
Signed-off-by: Greg Kroah-Hartman
19 Jul, 2007
1 commit
-
This interface allows the ability to write the majority of a driver in
userspace with only a very small shell of a driver in the kernel itself.
It uses a char device and sysfs to interact with a userspace process to
process interrupts and control memory accesses.See the docbook documentation for more details on how to use this
interface.From: Hans J. Koch
Cc: Thomas Gleixner
Cc: Benedikt Spranger
Signed-off-by: Greg Kroah-Hartman