1 =======================
2 The Userspace I/O HOWTO
3 =======================
4
5 :Author: Hans-Jürgen Koch Linux developer, Linutronix
6 :Date: 2006-12-11
7
8 About this document
9 ===================
10
11 Translations
12 ------------
13
14 If you know of any translations for this document, or you are interested
15 in translating it, please email me hjk@hansjkoch.de.
16
17 Preface
18 -------
19
20 For many types of devices, creating a Linux kernel driver is overkill.
21 All that is really needed is some way to handle an interrupt and provide
22 access to the memory space of the device. The logic of controlling the
23 device does not necessarily have to be within the kernel, as the device
24 does not need to take advantage of any of other resources that the
25 kernel provides. One such common class of devices that are like this are
26 for industrial I/O cards.
27
28 To address this situation, the userspace I/O system (UIO) was designed.
29 For typical industrial I/O cards, only a very small kernel module is
30 needed. The main part of the driver will run in user space. This
31 simplifies development and reduces the risk of serious bugs within a
32 kernel module.
33
34 Please note that UIO is not an universal driver interface. Devices that
35 are already handled well by other kernel subsystems (like networking or
36 serial or USB) are no candidates for an UIO driver. Hardware that is
37 ideally suited for an UIO driver fulfills all of the following:
38
39 - The device has memory that can be mapped. The device can be
40 controlled completely by writing to this memory.
41
42 - The device usually generates interrupts.
43
44 - The device does not fit into one of the standard kernel subsystems.
45
46 Acknowledgments
47 ---------------
48
49 I'd like to thank Thomas Gleixner and Benedikt Spranger of Linutronix,
50 who have not only written most of the UIO code, but also helped greatly
51 writing this HOWTO by giving me all kinds of background information.
52
53 Feedback
54 --------
55
56 Find something wrong with this document? (Or perhaps something right?) I
57 would love to hear from you. Please email me at hjk@hansjkoch.de.
58
59 About UIO
60 =========
61
62 If you use UIO for your card's driver, here's what you get:
63
64 - only one small kernel module to write and maintain.
65
66 - develop the main part of your driver in user space, with all the
67 tools and libraries you're used to.
68
69 - bugs in your driver won't crash the kernel.
70
71 - updates of your driver can take place without recompiling the kernel.
72
73 How UIO works
74 -------------
75
76 Each UIO device is accessed through a device file and several sysfs
77 attribute files. The device file will be called ``/dev/uio0`` for the
78 first device, and ``/dev/uio1``, ``/dev/uio2`` and so on for subsequent
79 devices.
80
81 ``/dev/uioX`` is used to access the address space of the card. Just use
82 :c:func:`mmap()` to access registers or RAM locations of your card.
83
84 Interrupts are handled by reading from ``/dev/uioX``. A blocking
85 :c:func:`read()` from ``/dev/uioX`` will return as soon as an
86 interrupt occurs. You can also use :c:func:`select()` on
87 ``/dev/uioX`` to wait for an interrupt. The integer value read from
88 ``/dev/uioX`` represents the total interrupt count. You can use this
89 number to figure out if you missed some interrupts.
90
91 For some hardware that has more than one interrupt source internally,
92 but not separate IRQ mask and status registers, there might be
93 situations where userspace cannot determine what the interrupt source
94 was if the kernel handler disables them by writing to the chip's IRQ
95 register. In such a case, the kernel has to disable the IRQ completely
96 to leave the chip's register untouched. Now the userspace part can
97 determine the cause of the interrupt, but it cannot re-enable
98 interrupts. Another cornercase is chips where re-enabling interrupts is
99 a read-modify-write operation to a combined IRQ status/acknowledge
100 register. This would be racy if a new interrupt occurred simultaneously.
101
102 To address these problems, UIO also implements a write() function. It is
103 normally not used and can be ignored for hardware that has only a single
104 interrupt source or has separate IRQ mask and status registers. If you
105 need it, however, a write to ``/dev/uioX`` will call the
106 :c:func:`irqcontrol()` function implemented by the driver. You have
107 to write a 32-bit value that is usually either 0 or 1 to disable or
108 enable interrupts. If a driver does not implement
109 :c:func:`irqcontrol()`, :c:func:`write()` will return with
110 ``-ENOSYS``.
111
112 To handle interrupts properly, your custom kernel module can provide its
113 own interrupt handler. It will automatically be called by the built-in
114 handler.
115
116 For cards that don't generate interrupts but need to be polled, there is
117 the possibility to set up a timer that triggers the interrupt handler at
118 configurable time intervals. This interrupt simulation is done by
119 calling :c:func:`uio_event_notify()` from the timer's event
120 handler.
121
122 Each driver provides attributes that are used to read or write
123 variables. These attributes are accessible through sysfs files. A custom
124 kernel driver module can add its own attributes to the device owned by
125 the uio driver, but not added to the UIO device itself at this time.
126 This might change in the future if it would be found to be useful.
127
128 The following standard attributes are provided by the UIO framework:
129
130 - ``name``: The name of your device. It is recommended to use the name
131 of your kernel module for this.
132
133 - ``version``: A version string defined by your driver. This allows the
134 user space part of your driver to deal with different versions of the
135 kernel module.
136
137 - ``event``: The total number of interrupts handled by the driver since
138 the last time the device node was read.
139
140 These attributes appear under the ``/sys/class/uio/uioX`` directory.
141 Please note that this directory might be a symlink, and not a real
142 directory. Any userspace code that accesses it must be able to handle
143 this.
144
145 Each UIO device can make one or more memory regions available for memory
146 mapping. This is necessary because some industrial I/O cards require
147 access to more than one PCI memory region in a driver.
148
149 Each mapping has its own directory in sysfs, the first mapping appears
150 as ``/sys/class/uio/uioX/maps/map0/``. Subsequent mappings create
151 directories ``map1/``, ``map2/``, and so on. These directories will only
152 appear if the size of the mapping is not 0.
153
154 Each ``mapX/`` directory contains four read-only files that show
155 attributes of the memory:
156
157 - ``name``: A string identifier for this mapping. This is optional, the
158 string can be empty. Drivers can set this to make it easier for
159 userspace to find the correct mapping.
160
161 - ``addr``: The address of memory that can be mapped.
162
163 - ``size``: The size, in bytes, of the memory pointed to by addr.
164
165 - ``offset``: The offset, in bytes, that has to be added to the pointer
166 returned by :c:func:`mmap()` to get to the actual device memory.
167 This is important if the device's memory is not page aligned.
168 Remember that pointers returned by :c:func:`mmap()` are always
169 page aligned, so it is good style to always add this offset.
170
171 From userspace, the different mappings are distinguished by adjusting
172 the ``offset`` parameter of the :c:func:`mmap()` call. To map the
173 memory of mapping N, you have to use N times the page size as your
174 offset::
175
176 offset = N * getpagesize();
177
178 Sometimes there is hardware with memory-like regions that can not be
179 mapped with the technique described here, but there are still ways to
180 access them from userspace. The most common example are x86 ioports. On
181 x86 systems, userspace can access these ioports using
182 :c:func:`ioperm()`, :c:func:`iopl()`, :c:func:`inb()`,
183 :c:func:`outb()`, and similar functions.
184
185 Since these ioport regions can not be mapped, they will not appear under
186 ``/sys/class/uio/uioX/maps/`` like the normal memory described above.
187 Without information about the port regions a hardware has to offer, it
188 becomes difficult for the userspace part of the driver to find out which
189 ports belong to which UIO device.
190
191 To address this situation, the new directory
192 ``/sys/class/uio/uioX/portio/`` was added. It only exists if the driver
193 wants to pass information about one or more port regions to userspace.
194 If that is the case, subdirectories named ``port0``, ``port1``, and so
195 on, will appear underneath ``/sys/class/uio/uioX/portio/``.
196
197 Each ``portX/`` directory contains four read-only files that show name,
198 start, size, and type of the port region:
199
200 - ``name``: A string identifier for this port region. The string is
201 optional and can be empty. Drivers can set it to make it easier for
202 userspace to find a certain port region.
203
204 - ``start``: The first port of this region.
205
206 - ``size``: The number of ports in this region.
207
208 - ``porttype``: A string describing the type of port.
209
210 Writing your own kernel module
211 ==============================
212
213 Please have a look at ``uio_cif.c`` as an example. The following
214 paragraphs explain the different sections of this file.
215
216 struct uio_info
217 ---------------
218
219 This structure tells the framework the details of your driver, Some of
220 the members are required, others are optional.
221
222 - ``const char *name``: Required. The name of your driver as it will
223 appear in sysfs. I recommend using the name of your module for this.
224
225 - ``const char *version``: Required. This string appears in
226 ``/sys/class/uio/uioX/version``.
227
228 - ``struct uio_mem mem[ MAX_UIO_MAPS ]``: Required if you have memory
229 that can be mapped with :c:func:`mmap()`. For each mapping you
230 need to fill one of the ``uio_mem`` structures. See the description
231 below for details.
232
233 - ``struct uio_port port[ MAX_UIO_PORTS_REGIONS ]``: Required if you
234 want to pass information about ioports to userspace. For each port
235 region you need to fill one of the ``uio_port`` structures. See the
236 description below for details.
237
238 - ``long irq``: Required. If your hardware generates an interrupt, it's
239 your modules task to determine the irq number during initialization.
240 If you don't have a hardware generated interrupt but want to trigger
241 the interrupt handler in some other way, set ``irq`` to
242 ``UIO_IRQ_CUSTOM``. If you had no interrupt at all, you could set
243 ``irq`` to ``UIO_IRQ_NONE``, though this rarely makes sense.
244
245 - ``unsigned long irq_flags``: Required if you've set ``irq`` to a
246 hardware interrupt number. The flags given here will be used in the
247 call to :c:func:`request_irq()`.
248
249 - ``int (*mmap)(struct uio_info *info, struct vm_area_struct *vma)``:
250 Optional. If you need a special :c:func:`mmap()`
251 function, you can set it here. If this pointer is not NULL, your
252 :c:func:`mmap()` will be called instead of the built-in one.
253
254 - ``int (*open)(struct uio_info *info, struct inode *inode)``:
255 Optional. You might want to have your own :c:func:`open()`,
256 e.g. to enable interrupts only when your device is actually used.
257
258 - ``int (*release)(struct uio_info *info, struct inode *inode)``:
259 Optional. If you define your own :c:func:`open()`, you will
260 probably also want a custom :c:func:`release()` function.
261
262 - ``int (*irqcontrol)(struct uio_info *info, s32 irq_on)``:
263 Optional. If you need to be able to enable or disable interrupts
264 from userspace by writing to ``/dev/uioX``, you can implement this
265 function. The parameter ``irq_on`` will be 0 to disable interrupts
266 and 1 to enable them.
267
268 Usually, your device will have one or more memory regions that can be
269 mapped to user space. For each region, you have to set up a
270 ``struct uio_mem`` in the ``mem[]`` array. Here's a description of the
271 fields of ``struct uio_mem``:
272
273 - ``const char *name``: Optional. Set this to help identify the memory
274 region, it will show up in the corresponding sysfs node.
275
276 - ``int memtype``: Required if the mapping is used. Set this to
277 ``UIO_MEM_PHYS`` if you have physical memory on your card to be
278 mapped. Use ``UIO_MEM_LOGICAL`` for logical memory (e.g. allocated
279 with :c:func:`__get_free_pages()` but not kmalloc()). There's also
280 ``UIO_MEM_VIRTUAL`` for virtual memory.
281
282 - ``phys_addr_t addr``: Required if the mapping is used. Fill in the
283 address of your memory block. This address is the one that appears in
284 sysfs.
285
286 - ``resource_size_t size``: Fill in the size of the memory block that
287 ``addr`` points to. If ``size`` is zero, the mapping is considered
288 unused. Note that you *must* initialize ``size`` with zero for all
289 unused mappings.
290
291 - ``void *internal_addr``: If you have to access this memory region
292 from within your kernel module, you will want to map it internally by
293 using something like :c:func:`ioremap()`. Addresses returned by
294 this function cannot be mapped to user space, so you must not store
295 it in ``addr``. Use ``internal_addr`` instead to remember such an
296 address.
297
298 Please do not touch the ``map`` element of ``struct uio_mem``! It is
299 used by the UIO framework to set up sysfs files for this mapping. Simply
300 leave it alone.
301
302 Sometimes, your device can have one or more port regions which can not
303 be mapped to userspace. But if there are other possibilities for
304 userspace to access these ports, it makes sense to make information
305 about the ports available in sysfs. For each region, you have to set up
306 a ``struct uio_port`` in the ``port[]`` array. Here's a description of
307 the fields of ``struct uio_port``:
308
309 - ``char *porttype``: Required. Set this to one of the predefined
310 constants. Use ``UIO_PORT_X86`` for the ioports found in x86
311 architectures.
312
313 - ``unsigned long start``: Required if the port region is used. Fill in
314 the number of the first port of this region.
315
316 - ``unsigned long size``: Fill in the number of ports in this region.
317 If ``size`` is zero, the region is considered unused. Note that you
318 *must* initialize ``size`` with zero for all unused regions.
319
320 Please do not touch the ``portio`` element of ``struct uio_port``! It is
321 used internally by the UIO framework to set up sysfs files for this
322 region. Simply leave it alone.
323
324 Adding an interrupt handler
325 ---------------------------
326
327 What you need to do in your interrupt handler depends on your hardware
328 and on how you want to handle it. You should try to keep the amount of
329 code in your kernel interrupt handler low. If your hardware requires no
330 action that you *have* to perform after each interrupt, then your
331 handler can be empty.
332
333 If, on the other hand, your hardware *needs* some action to be performed
334 after each interrupt, then you *must* do it in your kernel module. Note
335 that you cannot rely on the userspace part of your driver. Your
336 userspace program can terminate at any time, possibly leaving your
337 hardware in a state where proper interrupt handling is still required.
338
339 There might also be applications where you want to read data from your
340 hardware at each interrupt and buffer it in a piece of kernel memory
341 you've allocated for that purpose. With this technique you could avoid
342 loss of data if your userspace program misses an interrupt.
343
344 A note on shared interrupts: Your driver should support interrupt
345 sharing whenever this is possible. It is possible if and only if your
346 driver can detect whether your hardware has triggered the interrupt or
347 not. This is usually done by looking at an interrupt status register. If
348 your driver sees that the IRQ bit is actually set, it will perform its
349 actions, and the handler returns IRQ_HANDLED. If the driver detects
350 that it was not your hardware that caused the interrupt, it will do
351 nothing and return IRQ_NONE, allowing the kernel to call the next
352 possible interrupt handler.
353
354 If you decide not to support shared interrupts, your card won't work in
355 computers with no free interrupts. As this frequently happens on the PC
356 platform, you can save yourself a lot of trouble by supporting interrupt
357 sharing.
358
359 Using uio_pdrv for platform devices
360 -----------------------------------
361
362 In many cases, UIO drivers for platform devices can be handled in a
363 generic way. In the same place where you define your
364 ``struct platform_device``, you simply also implement your interrupt
365 handler and fill your ``struct uio_info``. A pointer to this
366 ``struct uio_info`` is then used as ``platform_data`` for your platform
367 device.
368
369 You also need to set up an array of ``struct resource`` containing
370 addresses and sizes of your memory mappings. This information is passed
371 to the driver using the ``.resource`` and ``.num_resources`` elements of
372 ``struct platform_device``.
373
374 You now have to set the ``.name`` element of ``struct platform_device``
375 to ``"uio_pdrv"`` to use the generic UIO platform device driver. This
376 driver will fill the ``mem[]`` array according to the resources given,
377 and register the device.
378
379 The advantage of this approach is that you only have to edit a file you
380 need to edit anyway. You do not have to create an extra driver.
381
382 Using uio_pdrv_genirq for platform devices
383 ------------------------------------------
384
385 Especially in embedded devices, you frequently find chips where the irq
386 pin is tied to its own dedicated interrupt line. In such cases, where
387 you can be really sure the interrupt is not shared, we can take the
388 concept of ``uio_pdrv`` one step further and use a generic interrupt
389 handler. That's what ``uio_pdrv_genirq`` does.
390
391 The setup for this driver is the same as described above for
392 ``uio_pdrv``, except that you do not implement an interrupt handler. The
393 ``.handler`` element of ``struct uio_info`` must remain ``NULL``. The
394 ``.irq_flags`` element must not contain ``IRQF_SHARED``.
395
396 You will set the ``.name`` element of ``struct platform_device`` to
397 ``"uio_pdrv_genirq"`` to use this driver.
398
399 The generic interrupt handler of ``uio_pdrv_genirq`` will simply disable
400 the interrupt line using :c:func:`disable_irq_nosync()`. After
401 doing its work, userspace can reenable the interrupt by writing
402 0x00000001 to the UIO device file. The driver already implements an
403 :c:func:`irq_control()` to make this possible, you must not
404 implement your own.
405
406 Using ``uio_pdrv_genirq`` not only saves a few lines of interrupt
407 handler code. You also do not need to know anything about the chip's
408 internal registers to create the kernel part of the driver. All you need
409 to know is the irq number of the pin the chip is connected to.
410
411 When used in a device-tree enabled system, the driver needs to be
412 probed with the ``"of_id"`` module parameter set to the ``"compatible"``
413 string of the node the driver is supposed to handle. By default, the
414 node's name (without the unit address) is exposed as name for the
415 UIO device in userspace. To set a custom name, a property named
416 ``"linux,uio-name"`` may be specified in the DT node.
417
418 Using uio_dmem_genirq for platform devices
419 ------------------------------------------
420
421 In addition to statically allocated memory ranges, they may also be a
422 desire to use dynamically allocated regions in a user space driver. In
423 particular, being able to access memory made available through the
424 dma-mapping API, may be particularly useful. The ``uio_dmem_genirq``
425 driver provides a way to accomplish this.
426
427 This driver is used in a similar manner to the ``"uio_pdrv_genirq"``
428 driver with respect to interrupt configuration and handling.
429
430 Set the ``.name`` element of ``struct platform_device`` to
431 ``"uio_dmem_genirq"`` to use this driver.
432
433 When using this driver, fill in the ``.platform_data`` element of
434 ``struct platform_device``, which is of type
435 ``struct uio_dmem_genirq_pdata`` and which contains the following
436 elements:
437
438 - ``struct uio_info uioinfo``: The same structure used as the
439 ``uio_pdrv_genirq`` platform data
440
441 - ``unsigned int *dynamic_region_sizes``: Pointer to list of sizes of
442 dynamic memory regions to be mapped into user space.
443
444 - ``unsigned int num_dynamic_regions``: Number of elements in
445 ``dynamic_region_sizes`` array.
446
447 The dynamic regions defined in the platform data will be appended to the
448 `` mem[] `` array after the platform device resources, which implies
449 that the total number of static and dynamic memory regions cannot exceed
450 ``MAX_UIO_MAPS``.
451
452 The dynamic memory regions will be allocated when the UIO device file,
453 ``/dev/uioX`` is opened. Similar to static memory resources, the memory
454 region information for dynamic regions is then visible via sysfs at
455 ``/sys/class/uio/uioX/maps/mapY/*``. The dynamic memory regions will be
456 freed when the UIO device file is closed. When no processes are holding
457 the device file open, the address returned to userspace is ~0.
458
459 Writing a driver in userspace
460 =============================
461
462 Once you have a working kernel module for your hardware, you can write
463 the userspace part of your driver. You don't need any special libraries,
464 your driver can be written in any reasonable language, you can use
465 floating point numbers and so on. In short, you can use all the tools
466 and libraries you'd normally use for writing a userspace application.
467
468 Getting information about your UIO device
469 -----------------------------------------
470
471 Information about all UIO devices is available in sysfs. The first thing
472 you should do in your driver is check ``name`` and ``version`` to make
473 sure you're talking to the right device and that its kernel driver has
474 the version you expect.
475
476 You should also make sure that the memory mapping you need exists and
477 has the size you expect.
478
479 There is a tool called ``lsuio`` that lists UIO devices and their
480 attributes. It is available here:
481
482 http://www.osadl.org/projects/downloads/UIO/user/
483
484 With ``lsuio`` you can quickly check if your kernel module is loaded and
485 which attributes it exports. Have a look at the manpage for details.
486
487 The source code of ``lsuio`` can serve as an example for getting
488 information about an UIO device. The file ``uio_helper.c`` contains a
489 lot of functions you could use in your userspace driver code.
490
491 mmap() device memory
492 --------------------
493
494 After you made sure you've got the right device with the memory mappings
495 you need, all you have to do is to call :c:func:`mmap()` to map the
496 device's memory to userspace.
497
498 The parameter ``offset`` of the :c:func:`mmap()` call has a special
499 meaning for UIO devices: It is used to select which mapping of your
500 device you want to map. To map the memory of mapping N, you have to use
501 N times the page size as your offset::
502
503 offset = N * getpagesize();
504
505 N starts from zero, so if you've got only one memory range to map, set
506 ``offset = 0``. A drawback of this technique is that memory is always
507 mapped beginning with its start address.
508
509 Waiting for interrupts
510 ----------------------
511
512 After you successfully mapped your devices memory, you can access it
513 like an ordinary array. Usually, you will perform some initialization.
514 After that, your hardware starts working and will generate an interrupt
515 as soon as it's finished, has some data available, or needs your
516 attention because an error occurred.
517
518 ``/dev/uioX`` is a read-only file. A :c:func:`read()` will always
519 block until an interrupt occurs. There is only one legal value for the
520 ``count`` parameter of :c:func:`read()`, and that is the size of a
521 signed 32 bit integer (4). Any other value for ``count`` causes
522 :c:func:`read()` to fail. The signed 32 bit integer read is the
523 interrupt count of your device. If the value is one more than the value
524 you read the last time, everything is OK. If the difference is greater
525 than one, you missed interrupts.
526
527 You can also use :c:func:`select()` on ``/dev/uioX``.
528
529 Generic PCI UIO driver
530 ======================
531
532 The generic driver is a kernel module named uio_pci_generic. It can
533 work with any device compliant to PCI 2.3 (circa 2002) and any compliant
534 PCI Express device. Using this, you only need to write the userspace
535 driver, removing the need to write a hardware-specific kernel module.
536
537 Making the driver recognize the device
538 --------------------------------------
539
540 Since the driver does not declare any device ids, it will not get loaded
541 automatically and will not automatically bind to any devices, you must
542 load it and allocate id to the driver yourself. For example::
543
544 modprobe uio_pci_generic
545 echo "8086 10f5" > /sys/bus/pci/drivers/uio_pci_generic/new_id
546
547 If there already is a hardware specific kernel driver for your device,
548 the generic driver still won't bind to it, in this case if you want to
549 use the generic driver (why would you?) you'll have to manually unbind
550 the hardware specific driver and bind the generic driver, like this::
551
552 echo -n 0000:00:19.0 > /sys/bus/pci/drivers/e1000e/unbind
553 echo -n 0000:00:19.0 > /sys/bus/pci/drivers/uio_pci_generic/bind
554
555 You can verify that the device has been bound to the driver by looking
556 for it in sysfs, for example like the following::
557
558 ls -l /sys/bus/pci/devices/0000:00:19.0/driver
559
560 Which if successful should print::
561
562 .../0000:00:19.0/driver -> ../../../bus/pci/drivers/uio_pci_generic
563
564 Note that the generic driver will not bind to old PCI 2.2 devices. If
565 binding the device failed, run the following command::
566
567 dmesg
568
569 and look in the output for failure reasons.
570
571 Things to know about uio_pci_generic
572 ------------------------------------
573
574 Interrupts are handled using the Interrupt Disable bit in the PCI
575 command register and Interrupt Status bit in the PCI status register.
576 All devices compliant to PCI 2.3 (circa 2002) and all compliant PCI
577 Express devices should support these bits. uio_pci_generic detects
578 this support, and won't bind to devices which do not support the
579 Interrupt Disable Bit in the command register.
580
581 On each interrupt, uio_pci_generic sets the Interrupt Disable bit.
582 This prevents the device from generating further interrupts until the
583 bit is cleared. The userspace driver should clear this bit before
584 blocking and waiting for more interrupts.
585
586 Writing userspace driver using uio_pci_generic
587 ------------------------------------------------
588
589 Userspace driver can use pci sysfs interface, or the libpci library that
590 wraps it, to talk to the device and to re-enable interrupts by writing
591 to the command register.
592
593 Example code using uio_pci_generic
594 ----------------------------------
595
596 Here is some sample userspace driver code using uio_pci_generic::
597
598 #include <stdlib.h>
599 #include <stdio.h>
600 #include <unistd.h>
601 #include <sys/types.h>
602 #include <sys/stat.h>
603 #include <fcntl.h>
604 #include <errno.h>
605
606 int main()
607 {
608 int uiofd;
609 int configfd;
610 int err;
611 int i;
612 unsigned icount;
613 unsigned char command_high;
614
615 uiofd = open("/dev/uio0", O_RDONLY);
616 if (uiofd < 0) {
617 perror("uio open:");
618 return errno;
619 }
620 configfd = open("/sys/class/uio/uio0/device/config", O_RDWR);
621 if (configfd < 0) {
622 perror("config open:");
623 return errno;
624 }
625
626 /* Read and cache command value */
627 err = pread(configfd, &command_high, 1, 5);
628 if (err != 1) {
629 perror("command config read:");
630 return errno;
631 }
632 command_high &= ~0x4;
633
634 for(i = 0;; ++i) {
635 /* Print out a message, for debugging. */
636 if (i == 0)
637 fprintf(stderr, "Started uio test driver.\n");
638 else
639 fprintf(stderr, "Interrupts: %d\n", icount);
640
641 /****************************************/
642 /* Here we got an interrupt from the
643 device. Do something to it. */
644 /****************************************/
645
646 /* Re-enable interrupts. */
647 err = pwrite(configfd, &command_high, 1, 5);
648 if (err != 1) {
649 perror("config write:");
650 break;
651 }
652
653 /* Wait for next interrupt. */
654 err = read(uiofd, &icount, 4);
655 if (err != 4) {
656 perror("uio read:");
657 break;
658 }
659
660 }
661 return errno;
662 }
663
664 Generic Hyper-V UIO driver
665 ==========================
666
667 The generic driver is a kernel module named uio_hv_generic. It
668 supports devices on the Hyper-V VMBus similar to uio_pci_generic on
669 PCI bus.
670
671 Making the driver recognize the device
672 --------------------------------------
673
674 Since the driver does not declare any device GUID's, it will not get
675 loaded automatically and will not automatically bind to any devices, you
676 must load it and allocate id to the driver yourself. For example, to use
677 the network device class GUID::
678
679 modprobe uio_hv_generic
680 echo "f8615163-df3e-46c5-913f-f2d2f965ed0e" > /sys/bus/vmbus/drivers/uio_hv_generic/new_id
681
682 If there already is a hardware specific kernel driver for the device,
683 the generic driver still won't bind to it, in this case if you want to
684 use the generic driver for a userspace library you'll have to manually unbind
685 the hardware specific driver and bind the generic driver, using the device specific GUID
686 like this::
687
688 echo -n ed963694-e847-4b2a-85af-bc9cfc11d6f3 > /sys/bus/vmbus/drivers/hv_netvsc/unbind
689 echo -n ed963694-e847-4b2a-85af-bc9cfc11d6f3 > /sys/bus/vmbus/drivers/uio_hv_generic/bind
690
691 You can verify that the device has been bound to the driver by looking
692 for it in sysfs, for example like the following::
693
694 ls -l /sys/bus/vmbus/devices/ed963694-e847-4b2a-85af-bc9cfc11d6f3/driver
695
696 Which if successful should print::
697
698 .../ed963694-e847-4b2a-85af-bc9cfc11d6f3/driver -> ../../../bus/vmbus/drivers/uio_hv_generic
699
700 Things to know about uio_hv_generic
701 -----------------------------------
702
703 On each interrupt, uio_hv_generic sets the Interrupt Disable bit. This
704 prevents the device from generating further interrupts until the bit is
705 cleared. The userspace driver should clear this bit before blocking and
706 waiting for more interrupts.
707
708 When host rescinds a device, the interrupt file descriptor is marked down
709 and any reads of the interrupt file descriptor will return -EIO. Similar
710 to a closed socket or disconnected serial device.
711
712 The vmbus device regions are mapped into uio device resources:
713 0) Channel ring buffers: guest to host and host to guest
714 1) Guest to host interrupt signalling pages
715 2) Guest to host monitor page
716 3) Network receive buffer region
717 4) Network send buffer region
718
719 If a subchannel is created by a request to host, then the uio_hv_generic
720 device driver will create a sysfs binary file for the per-channel ring buffer.
721 For example::
722
723 /sys/bus/vmbus/devices/3811fe4d-0fa0-4b62-981a-74fc1084c757/channels/21/ring
724
725 Further information
726 ===================
727
728 - `OSADL homepage. <http://www.osadl.org>`_
729
730 - `Linutronix homepage. <http://www.linutronix.de>`_
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