The Userspace I/O HOWTO

From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751425AbdA0UKD (ORCPT ); Fri, 27 Jan 2017 15:10:03 -0500 Received: from mout.kundenserver.de ([212.227.126.187]:55995 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751049AbdA0UJ7 (ORCPT ); Fri, 27 Jan 2017 15:09:59 -0500 From: Alexander Dahl To: linux-kernel@vger.kernel.org Cc: Alexander Dahl , =?UTF-8?q?Hans-J=C3=BCrgen=20Koch?= , Greg Kroah-Hartman Subject: [PATCH] doc: convert UIO howto from docbook to sphinx Date: Fri, 27 Jan 2017 21:08:27 +0100 Message-Id: <1485547707-2253-1-git-send-email-post@lespocky.de> X-Mailer: git-send-email 2.1.4 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Scan-Signature: 8ad2d3403209d026f873f7885c3d7c3b X-Spam-Score: -5.3 (-----) X-Provags-ID: V03:K0:HNOyZfFBYTr9E9qyX1s372m0rxXaSEgJNBSCIDLANIcbp7PwG85 fevNGdWGpbEEx+Fkhabf0aH65xSp/zmHLqjvLUcPknWWAuu91Q/PsaWj0uWCCVfZWbIhBy6 KYIEAIApkmKKJYl1n9054q8xuNfrLjNvcPLnlX8TkXN0hJgho8mwrF3mY+8Zcx/GxbKLws1 HaWj+s69YF0CTo3zDd9Tw== X-UI-Out-Filterresults: notjunk:1;V01:K0:264bLC/07xo=:xPhUVvSgEYllQECZH9PWop VSL1F+Ani8FMdE7tD4n0cRDl29riW44OtG48KUXSipIkMTiEa56rPibaHjmLGu2lkE18EL3fi g85dLLFsE3cLUc9d06Hs+uPEa3IO4/LsPXhCnz1Z/cBLAvHdFBmACmzkGzPOwJ4YgZC+Vu8yW 8P1GDT6aNSlbN9jgUp2ld1LdIqTH9EKlFThR3UYqXhQZq0YwkRTRZSQClDaKmYDwgAiEvcTdp YvFc5CFcyjigSYv8m2fqdlq8LVlXvfjlYUiJaoMcvAo6A2rlRhP8hv7PxtEi11O5dYx/Vzd9v maccQndzByaeJcDOYe2VX3miPTrO4V6+xmog7chTDzfbkORz4lN1Pjgvf8geSoWH9QDpO6oEA raMCJUYoCTGEWvC4wdg7ew6nxESlwzepBEORbnaYPLnpReZjU5VYMRrjx6ifCPQZ4ArWsopid E+ul6haA5e0ji+3YFuiX3J+TQaFQlOZudzkua/suVYBnAjOPq0RB6Z5XgprOwi1vmzvyCm4IT yUrM9GwTYUwQxj2N2jEbP/Mt7ILxdGcGnm6iv1qwZwGs+DdYOyP04q1bYHiOJAvNMUu0s7mzS 4nZZETr8n2aW5YcoJ6xh4BYSIJrzDinAzusTIuY/5DnRQeB0tts7HDhksAv+wYAhYEWpXJe+y dKLZThNcCxL2D725QOFFAAPjpyDHh7FD9xX9x2T8mSqkm2SAAbnLQ/hGSsvyZlipKBLc4J/Zu jFKP21uUpr5uGGB7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Converted with tmplcvt. Only some tiny things needed manual fixing. Signed-off-by: Alexander Dahl Cc: Hans-Jürgen Koch Cc: Greg Kroah-Hartman --- based on v4.10-rc4 --- Documentation/DocBook/uio-howto.tmpl | 1112 -------------------------------- Documentation/driver-api/index.rst | 1 + Documentation/driver-api/uio-howto.rst | 705 ++++++++++++++++++++ MAINTAINERS | 2 +- 4 files changed, 707 insertions(+), 1113 deletions(-) delete mode 100644 Documentation/DocBook/uio-howto.tmpl create mode 100644 Documentation/driver-api/uio-howto.rst diff --git a/Documentation/DocBook/uio-howto.tmpl b/Documentation/DocBook/uio-howto.tmpl deleted file mode 100644 index 5210f8a..0000000 --- a/Documentation/DocBook/uio-howto.tmpl +++ /dev/null @@ -1,1112 +0,0 @@ - - - - - -The Userspace I/O HOWTO - - - Hans-Jürgen - Koch - Linux developer, Linutronix - - - Linutronix - - -

- hjk@hansjkoch.de -

- - - - - 2006-2008 - Hans-Jürgen Koch. - - - 2009 - Red Hat Inc, Michael S. Tsirkin (mst@redhat.com) - - - - -This documentation is Free Software licensed under the terms of the -GPL version 2. - - - -2006-12-11 - - - This HOWTO describes concept and usage of Linux kernel's - Userspace I/O system. - - - - - 0.10 - 2016-10-17 - sch - Added generic hyperv driver - - - - 0.9 - 2009-07-16 - mst - Added generic pci driver - - - - 0.8 - 2008-12-24 - hjk - Added name attributes in mem and portio sysfs directories. - - - - 0.7 - 2008-12-23 - hjk - Added generic platform drivers and offset attribute. - - - 0.6 - 2008-12-05 - hjk - Added description of portio sysfs attributes. - - - 0.5 - 2008-05-22 - hjk - Added description of write() function. - - - 0.4 - 2007-11-26 - hjk - Removed section about uio_dummy. - - - 0.3 - 2007-04-29 - hjk - Added section about userspace drivers. - - - 0.2 - 2007-02-13 - hjk - Update after multiple mappings were added. - - - 0.1 - 2006-12-11 - hjk - First draft. - - - - - - -About this document - - - -Translations - -If you know of any translations for this document, or you are -interested in translating it, please email me -hjk@hansjkoch.de. - - - - -Preface - - For many types of devices, creating a Linux kernel driver is - overkill. All that is really needed is some way to handle an - interrupt and provide access to the memory space of the - device. The logic of controlling the device does not - necessarily have to be within the kernel, as the device does - not need to take advantage of any of other resources that the - kernel provides. One such common class of devices that are - like this are for industrial I/O cards. - - - To address this situation, the userspace I/O system (UIO) was - designed. For typical industrial I/O cards, only a very small - kernel module is needed. The main part of the driver will run in - user space. This simplifies development and reduces the risk of - serious bugs within a kernel module. - - - Please note that UIO is not an universal driver interface. Devices - that are already handled well by other kernel subsystems (like - networking or serial or USB) are no candidates for an UIO driver. - Hardware that is ideally suited for an UIO driver fulfills all of - the following: - - - - The device has memory that can be mapped. The device can be - controlled completely by writing to this memory. - - - The device usually generates interrupts. - - - The device does not fit into one of the standard kernel - subsystems. - - - - - -Acknowledgments - I'd like to thank Thomas Gleixner and Benedikt Spranger of - Linutronix, who have not only written most of the UIO code, but also - helped greatly writing this HOWTO by giving me all kinds of background - information. - - - -Feedback - Find something wrong with this document? (Or perhaps something - right?) I would love to hear from you. Please email me at - hjk@hansjkoch.de. - - - - - -About UIO - -If you use UIO for your card's driver, here's what you get: - - - - only one small kernel module to write and maintain. - - - develop the main part of your driver in user space, - with all the tools and libraries you're used to. - - - bugs in your driver won't crash the kernel. - - - updates of your driver can take place without recompiling - the kernel. - - - - -How UIO works - - Each UIO device is accessed through a device file and several - sysfs attribute files. The device file will be called - /dev/uio0 for the first device, and - /dev/uio1, /dev/uio2 - and so on for subsequent devices. - - - /dev/uioX is used to access the - address space of the card. Just use - mmap() to access registers or RAM - locations of your card. - - - - Interrupts are handled by reading from - /dev/uioX. A blocking - read() from - /dev/uioX will return as soon as an - interrupt occurs. You can also use - select() on - /dev/uioX to wait for an interrupt. The - integer value read from /dev/uioX - represents the total interrupt count. You can use this number - to figure out if you missed some interrupts. - - - For some hardware that has more than one interrupt source internally, - but not separate IRQ mask and status registers, there might be - situations where userspace cannot determine what the interrupt source - was if the kernel handler disables them by writing to the chip's IRQ - register. In such a case, the kernel has to disable the IRQ completely - to leave the chip's register untouched. Now the userspace part can - determine the cause of the interrupt, but it cannot re-enable - interrupts. Another cornercase is chips where re-enabling interrupts - is a read-modify-write operation to a combined IRQ status/acknowledge - register. This would be racy if a new interrupt occurred - simultaneously. - - - To address these problems, UIO also implements a write() function. It - is normally not used and can be ignored for hardware that has only a - single interrupt source or has separate IRQ mask and status registers. - If you need it, however, a write to /dev/uioX - will call the irqcontrol() function implemented - by the driver. You have to write a 32-bit value that is usually either - 0 or 1 to disable or enable interrupts. If a driver does not implement - irqcontrol(), write() will - return with -ENOSYS. - - - - To handle interrupts properly, your custom kernel module can - provide its own interrupt handler. It will automatically be - called by the built-in handler. - - - - For cards that don't generate interrupts but need to be - polled, there is the possibility to set up a timer that - triggers the interrupt handler at configurable time intervals. - This interrupt simulation is done by calling - uio_event_notify() - from the timer's event handler. - - - - Each driver provides attributes that are used to read or write - variables. These attributes are accessible through sysfs - files. A custom kernel driver module can add its own - attributes to the device owned by the uio driver, but not added - to the UIO device itself at this time. This might change in the - future if it would be found to be useful. - - - - The following standard attributes are provided by the UIO - framework: - - - - - name: The name of your device. It is - recommended to use the name of your kernel module for this. - - - - - version: A version string defined by your - driver. This allows the user space part of your driver to deal - with different versions of the kernel module. - - - - - event: The total number of interrupts - handled by the driver since the last time the device node was - read. - - - - - These attributes appear under the - /sys/class/uio/uioX directory. Please - note that this directory might be a symlink, and not a real - directory. Any userspace code that accesses it must be able - to handle this. - - - Each UIO device can make one or more memory regions available for - memory mapping. This is necessary because some industrial I/O cards - require access to more than one PCI memory region in a driver. - - - Each mapping has its own directory in sysfs, the first mapping - appears as /sys/class/uio/uioX/maps/map0/. - Subsequent mappings create directories map1/, - map2/, and so on. These directories will only - appear if the size of the mapping is not 0. - - - Each mapX/ directory contains four read-only files - that show attributes of the memory: - - - - - name: A string identifier for this mapping. This - is optional, the string can be empty. Drivers can set this to make it - easier for userspace to find the correct mapping. - - - - - addr: The address of memory that can be mapped. - - - - - size: The size, in bytes, of the memory - pointed to by addr. - - - - - offset: The offset, in bytes, that has to be - added to the pointer returned by mmap() to get - to the actual device memory. This is important if the device's memory - is not page aligned. Remember that pointers returned by - mmap() are always page aligned, so it is good - style to always add this offset. - - - - - - From userspace, the different mappings are distinguished by adjusting - the offset parameter of the - mmap() call. To map the memory of mapping N, you - have to use N times the page size as your offset: - - -offset = N * getpagesize(); - - - - Sometimes there is hardware with memory-like regions that can not be - mapped with the technique described here, but there are still ways to - access them from userspace. The most common example are x86 ioports. - On x86 systems, userspace can access these ioports using - ioperm(), iopl(), - inb(), outb(), and similar - functions. - - - Since these ioport regions can not be mapped, they will not appear under - /sys/class/uio/uioX/maps/ like the normal memory - described above. Without information about the port regions a hardware - has to offer, it becomes difficult for the userspace part of the - driver to find out which ports belong to which UIO device. - - - To address this situation, the new directory - /sys/class/uio/uioX/portio/ was added. It only - exists if the driver wants to pass information about one or more port - regions to userspace. If that is the case, subdirectories named - port0, port1, and so on, - will appear underneath - /sys/class/uio/uioX/portio/. - - - Each portX/ directory contains four read-only - files that show name, start, size, and type of the port region: - - - - - name: A string identifier for this port region. - The string is optional and can be empty. Drivers can set it to make it - easier for userspace to find a certain port region. - - - - - start: The first port of this region. - - - - - size: The number of ports in this region. - - - - - porttype: A string describing the type of port. - - - - - - - - - - -Writing your own kernel module - - Please have a look at uio_cif.c as an - example. The following paragraphs explain the different - sections of this file. - - - -struct uio_info - - This structure tells the framework the details of your driver, - Some of the members are required, others are optional. - - - - -const char *name: Required. The name of your driver as -it will appear in sysfs. I recommend using the name of your module for this. - - - -const char *version: Required. This string appears in -/sys/class/uio/uioX/version. - - - -struct uio_mem mem[ MAX_UIO_MAPS ]: Required if you -have memory that can be mapped with mmap(). For each -mapping you need to fill one of the uio_mem structures. -See the description below for details. - - - -struct uio_port port[ MAX_UIO_PORTS_REGIONS ]: Required -if you want to pass information about ioports to userspace. For each port -region you need to fill one of the uio_port structures. -See the description below for details. - - - -long irq: Required. If your hardware generates an -interrupt, it's your modules task to determine the irq number during -initialization. If you don't have a hardware generated interrupt but -want to trigger the interrupt handler in some other way, set -irq to UIO_IRQ_CUSTOM. -If you had no interrupt at all, you could set -irq to UIO_IRQ_NONE, though this -rarely makes sense. - - - -unsigned long irq_flags: Required if you've set -irq to a hardware interrupt number. The flags given -here will be used in the call to request_irq(). - - - -int (*mmap)(struct uio_info *info, struct vm_area_struct -*vma): Optional. If you need a special -mmap() function, you can set it here. If this -pointer is not NULL, your mmap() will be called -instead of the built-in one. - - - -int (*open)(struct uio_info *info, struct inode *inode) -: Optional. You might want to have your own -open(), e.g. to enable interrupts only when your -device is actually used. - - - -int (*release)(struct uio_info *info, struct inode *inode) -: Optional. If you define your own -open(), you will probably also want a custom -release() function. - - - -int (*irqcontrol)(struct uio_info *info, s32 irq_on) -: Optional. If you need to be able to enable or disable -interrupts from userspace by writing to /dev/uioX, -you can implement this function. The parameter irq_on -will be 0 to disable interrupts and 1 to enable them. - - - - -Usually, your device will have one or more memory regions that can be mapped -to user space. For each region, you have to set up a -struct uio_mem in the mem[] array. -Here's a description of the fields of struct uio_mem: - - - - -const char *name: Optional. Set this to help identify -the memory region, it will show up in the corresponding sysfs node. - - - -int memtype: Required if the mapping is used. Set this to -UIO_MEM_PHYS if you you have physical memory on your -card to be mapped. Use UIO_MEM_LOGICAL for logical -memory (e.g. allocated with kmalloc()). There's also -UIO_MEM_VIRTUAL for virtual memory. - - - -phys_addr_t addr: Required if the mapping is used. -Fill in the address of your memory block. This address is the one that -appears in sysfs. - - - -resource_size_t size: Fill in the size of the -memory block that addr points to. If size -is zero, the mapping is considered unused. Note that you -must initialize size with zero for -all unused mappings. - - - -void *internal_addr: If you have to access this memory -region from within your kernel module, you will want to map it internally by -using something like ioremap(). Addresses -returned by this function cannot be mapped to user space, so you must not -store it in addr. Use internal_addr -instead to remember such an address. - - - - -Please do not touch the map element of -struct uio_mem! It is used by the UIO framework -to set up sysfs files for this mapping. Simply leave it alone. - - - -Sometimes, your device can have one or more port regions which can not be -mapped to userspace. But if there are other possibilities for userspace to -access these ports, it makes sense to make information about the ports -available in sysfs. For each region, you have to set up a -struct uio_port in the port[] array. -Here's a description of the fields of struct uio_port: - - - - -char *porttype: Required. Set this to one of the predefined -constants. Use UIO_PORT_X86 for the ioports found in x86 -architectures. - - - -unsigned long start: Required if the port region is used. -Fill in the number of the first port of this region. - - - -unsigned long size: Fill in the number of ports in this -region. If size is zero, the region is considered unused. -Note that you must initialize size -with zero for all unused regions. - - - - -Please do not touch the portio element of -struct uio_port! It is used internally by the UIO -framework to set up sysfs files for this region. Simply leave it alone. - - - - - -Adding an interrupt handler - - What you need to do in your interrupt handler depends on your - hardware and on how you want to handle it. You should try to - keep the amount of code in your kernel interrupt handler low. - If your hardware requires no action that you - have to perform after each interrupt, - then your handler can be empty. If, on the other - hand, your hardware needs some action to - be performed after each interrupt, then you - must do it in your kernel module. Note - that you cannot rely on the userspace part of your driver. Your - userspace program can terminate at any time, possibly leaving - your hardware in a state where proper interrupt handling is - still required. - - - - There might also be applications where you want to read data - from your hardware at each interrupt and buffer it in a piece - of kernel memory you've allocated for that purpose. With this - technique you could avoid loss of data if your userspace - program misses an interrupt. - - - - A note on shared interrupts: Your driver should support - interrupt sharing whenever this is possible. It is possible if - and only if your driver can detect whether your hardware has - triggered the interrupt or not. This is usually done by looking - at an interrupt status register. If your driver sees that the - IRQ bit is actually set, it will perform its actions, and the - handler returns IRQ_HANDLED. If the driver detects that it was - not your hardware that caused the interrupt, it will do nothing - and return IRQ_NONE, allowing the kernel to call the next - possible interrupt handler. - - - - If you decide not to support shared interrupts, your card - won't work in computers with no free interrupts. As this - frequently happens on the PC platform, you can save yourself a - lot of trouble by supporting interrupt sharing. - - - - -Using uio_pdrv for platform devices - - In many cases, UIO drivers for platform devices can be handled in a - generic way. In the same place where you define your - struct platform_device, you simply also implement - your interrupt handler and fill your - struct uio_info. A pointer to this - struct uio_info is then used as - platform_data for your platform device. - - - You also need to set up an array of struct resource - containing addresses and sizes of your memory mappings. This - information is passed to the driver using the - .resource and .num_resources - elements of struct platform_device. - - - You now have to set the .name element of - struct platform_device to - "uio_pdrv" to use the generic UIO platform device - driver. This driver will fill the mem[] array - according to the resources given, and register the device. - - - The advantage of this approach is that you only have to edit a file - you need to edit anyway. You do not have to create an extra driver. - - - - -Using uio_pdrv_genirq for platform devices - - Especially in embedded devices, you frequently find chips where the - irq pin is tied to its own dedicated interrupt line. In such cases, - where you can be really sure the interrupt is not shared, we can take - the concept of uio_pdrv one step further and use a - generic interrupt handler. That's what - uio_pdrv_genirq does. - - - The setup for this driver is the same as described above for - uio_pdrv, except that you do not implement an - interrupt handler. The .handler element of - struct uio_info must remain - NULL. The .irq_flags element - must not contain IRQF_SHARED. - - - You will set the .name element of - struct platform_device to - "uio_pdrv_genirq" to use this driver. - - - The generic interrupt handler of uio_pdrv_genirq - will simply disable the interrupt line using - disable_irq_nosync(). After doing its work, - userspace can reenable the interrupt by writing 0x00000001 to the UIO - device file. The driver already implements an - irq_control() to make this possible, you must not - implement your own. - - - Using uio_pdrv_genirq not only saves a few lines of - interrupt handler code. You also do not need to know anything about - the chip's internal registers to create the kernel part of the driver. - All you need to know is the irq number of the pin the chip is - connected to. - - - - -Using uio_dmem_genirq for platform devices - - In addition to statically allocated memory ranges, they may also be - a desire to use dynamically allocated regions in a user space driver. - In particular, being able to access memory made available through the - dma-mapping API, may be particularly useful. The - uio_dmem_genirq driver provides a way to accomplish - this. - - - This driver is used in a similar manner to the - "uio_pdrv_genirq" driver with respect to interrupt - configuration and handling. - - - Set the .name element of - struct platform_device to - "uio_dmem_genirq" to use this driver. - - - When using this driver, fill in the .platform_data - element of struct platform_device, which is of type - struct uio_dmem_genirq_pdata and which contains the - following elements: - - - struct uio_info uioinfo: The same - structure used as the uio_pdrv_genirq platform - data - unsigned int *dynamic_region_sizes: - Pointer to list of sizes of dynamic memory regions to be mapped into - user space. - - unsigned int num_dynamic_regions: - Number of elements in dynamic_region_sizes array. - - - - The dynamic regions defined in the platform data will be appended to - the mem[] array after the platform device - resources, which implies that the total number of static and dynamic - memory regions cannot exceed MAX_UIO_MAPS. - - - The dynamic memory regions will be allocated when the UIO device file, - /dev/uioX is opened. - Similar to static memory resources, the memory region information for - dynamic regions is then visible via sysfs at - /sys/class/uio/uioX/maps/mapY/*. - The dynamic memory regions will be freed when the UIO device file is - closed. When no processes are holding the device file open, the address - returned to userspace is ~0. - - - - - - - -Writing a driver in userspace - - Once you have a working kernel module for your hardware, you can - write the userspace part of your driver. You don't need any special - libraries, your driver can be written in any reasonable language, - you can use floating point numbers and so on. In short, you can - use all the tools and libraries you'd normally use for writing a - userspace application. - - - -Getting information about your UIO device - - Information about all UIO devices is available in sysfs. The - first thing you should do in your driver is check - name and version to - make sure your talking to the right device and that its kernel - driver has the version you expect. - - - You should also make sure that the memory mapping you need - exists and has the size you expect. - - - There is a tool called lsuio that lists - UIO devices and their attributes. It is available here: - - - - http://www.osadl.org/projects/downloads/UIO/user/ - - - With lsuio you can quickly check if your - kernel module is loaded and which attributes it exports. - Have a look at the manpage for details. - - - The source code of lsuio can serve as an - example for getting information about an UIO device. - The file uio_helper.c contains a lot of - functions you could use in your userspace driver code. - - - - -mmap() device memory - - After you made sure you've got the right device with the - memory mappings you need, all you have to do is to call - mmap() to map the device's memory - to userspace. - - - The parameter offset of the - mmap() call has a special meaning - for UIO devices: It is used to select which mapping of - your device you want to map. To map the memory of - mapping N, you have to use N times the page size as - your offset: - - - offset = N * getpagesize(); - - - N starts from zero, so if you've got only one memory - range to map, set offset = 0. - A drawback of this technique is that memory is always - mapped beginning with its start address. - - - - -Waiting for interrupts - - After you successfully mapped your devices memory, you - can access it like an ordinary array. Usually, you will - perform some initialization. After that, your hardware - starts working and will generate an interrupt as soon - as it's finished, has some data available, or needs your - attention because an error occurred. - - - /dev/uioX is a read-only file. A - read() will always block until an - interrupt occurs. There is only one legal value for the - count parameter of - read(), and that is the size of a - signed 32 bit integer (4). Any other value for - count causes read() - to fail. The signed 32 bit integer read is the interrupt - count of your device. If the value is one more than the value - you read the last time, everything is OK. If the difference - is greater than one, you missed interrupts. - - - You can also use select() on - /dev/uioX. - - - - - - - -Generic PCI UIO driver - - The generic driver is a kernel module named uio_pci_generic. - It can work with any device compliant to PCI 2.3 (circa 2002) and - any compliant PCI Express device. Using this, you only need to - write the userspace driver, removing the need to write - a hardware-specific kernel module. - - - -Making the driver recognize the device - -Since the driver does not declare any device ids, it will not get loaded -automatically and will not automatically bind to any devices, you must load it -and allocate id to the driver yourself. For example: - - modprobe uio_pci_generic - echo "8086 10f5" > /sys/bus/pci/drivers/uio_pci_generic/new_id - - - -If there already is a hardware specific kernel driver for your device, the -generic driver still won't bind to it, in this case if you want to use the -generic driver (why would you?) you'll have to manually unbind the hardware -specific driver and bind the generic driver, like this: - - echo -n 0000:00:19.0 > /sys/bus/pci/drivers/e1000e/unbind - echo -n 0000:00:19.0 > /sys/bus/pci/drivers/uio_pci_generic/bind - - - -You can verify that the device has been bound to the driver -by looking for it in sysfs, for example like the following: - - ls -l /sys/bus/pci/devices/0000:00:19.0/driver - -Which if successful should print - - .../0000:00:19.0/driver -> ../../../bus/pci/drivers/uio_pci_generic - -Note that the generic driver will not bind to old PCI 2.2 devices. -If binding the device failed, run the following command: - - dmesg - -and look in the output for failure reasons - - - - -Things to know about uio_pci_generic - -Interrupts are handled using the Interrupt Disable bit in the PCI command -register and Interrupt Status bit in the PCI status register. All devices -compliant to PCI 2.3 (circa 2002) and all compliant PCI Express devices should -support these bits. uio_pci_generic detects this support, and won't bind to -devices which do not support the Interrupt Disable Bit in the command register. - - -On each interrupt, uio_pci_generic sets the Interrupt Disable bit. -This prevents the device from generating further interrupts -until the bit is cleared. The userspace driver should clear this -bit before blocking and waiting for more interrupts. - - - -Writing userspace driver using uio_pci_generic - -Userspace driver can use pci sysfs interface, or the -libpci libray that wraps it, to talk to the device and to -re-enable interrupts by writing to the command register. - - - -Example code using uio_pci_generic - -Here is some sample userspace driver code using uio_pci_generic: - -#include <stdlib.h> -#include <stdio.h> -#include <unistd.h> -#include <sys/types.h> -#include <sys/stat.h> -#include <fcntl.h> -#include <errno.h> - -int main() -{ - int uiofd; - int configfd; - int err; - int i; - unsigned icount; - unsigned char command_high; - - uiofd = open("/dev/uio0", O_RDONLY); - if (uiofd < 0) { - perror("uio open:"); - return errno; - } - configfd = open("/sys/class/uio/uio0/device/config", O_RDWR); - if (configfd < 0) { - perror("config open:"); - return errno; - } - - /* Read and cache command value */ - err = pread(configfd, &command_high, 1, 5); - if (err != 1) { - perror("command config read:"); - return errno; - } - command_high &= ~0x4; - - for(i = 0;; ++i) { - /* Print out a message, for debugging. */ - if (i == 0) - fprintf(stderr, "Started uio test driver.\n"); - else - fprintf(stderr, "Interrupts: %d\n", icount); - - /****************************************/ - /* Here we got an interrupt from the - device. Do something to it. */ - /****************************************/ - - /* Re-enable interrupts. */ - err = pwrite(configfd, &command_high, 1, 5); - if (err != 1) { - perror("config write:"); - break; - } - - /* Wait for next interrupt. */ - err = read(uiofd, &icount, 4); - if (err != 4) { - perror("uio read:"); - break; - } - - } - return errno; -} - - - - - - - - - -Generic Hyper-V UIO driver - - The generic driver is a kernel module named uio_hv_generic. - It supports devices on the Hyper-V VMBus similar to uio_pci_generic - on PCI bus. - - - -Making the driver recognize the device - -Since the driver does not declare any device GUID's, it will not get loaded -automatically and will not automatically bind to any devices, you must load it -and allocate id to the driver yourself. For example, to use the network device -GUID: - - modprobe uio_hv_generic - echo "f8615163-df3e-46c5-913f-f2d2f965ed0e" > /sys/bus/vmbus/drivers/uio_hv_generic/new_id - - - -If there already is a hardware specific kernel driver for the device, the -generic driver still won't bind to it, in this case if you want to use the -generic driver (why would you?) you'll have to manually unbind the hardware -specific driver and bind the generic driver, like this: - - echo -n vmbus-ed963694-e847-4b2a-85af-bc9cfc11d6f3 > /sys/bus/vmbus/drivers/hv_netvsc/unbind - echo -n vmbus-ed963694-e847-4b2a-85af-bc9cfc11d6f3 > /sys/bus/vmbus/drivers/uio_hv_generic/bind - - - -You can verify that the device has been bound to the driver -by looking for it in sysfs, for example like the following: - - ls -l /sys/bus/vmbus/devices/vmbus-ed963694-e847-4b2a-85af-bc9cfc11d6f3/driver - -Which if successful should print - - .../vmbus-ed963694-e847-4b2a-85af-bc9cfc11d6f3/driver -> ../../../bus/vmbus/drivers/uio_hv_generic - - - - - -Things to know about uio_hv_generic - -On each interrupt, uio_hv_generic sets the Interrupt Disable bit. -This prevents the device from generating further interrupts -until the bit is cleared. The userspace driver should clear this -bit before blocking and waiting for more interrupts. - - - - - -Further information - - - - OSADL homepage. - - - - Linutronix homepage. - - - - - diff --git a/Documentation/driver-api/index.rst b/Documentation/driver-api/index.rst index 5475a28..c5a1cd0 100644 --- a/Documentation/driver-api/index.rst +++ b/Documentation/driver-api/index.rst @@ -30,6 +30,7 @@ available subsections can be seen below. miscellaneous vme 80211/index + uio-howto .. only:: subproject and html diff --git a/Documentation/driver-api/uio-howto.rst b/Documentation/driver-api/uio-howto.rst new file mode 100644 index 0000000..f73d660 --- /dev/null +++ b/Documentation/driver-api/uio-howto.rst @@ -0,0 +1,705 @@ +======================= +The Userspace I/O HOWTO +======================= + +:Author: Hans-Jürgen Koch Linux developer, Linutronix +:Date: 2006-12-11 + +About this document +=================== + +Translations +------------ + +If you know of any translations for this document, or you are interested +in translating it, please email me hjk@hansjkoch.de. + +Preface +------- + +For many types of devices, creating a Linux kernel driver is overkill. +All that is really needed is some way to handle an interrupt and provide +access to the memory space of the device. The logic of controlling the +device does not necessarily have to be within the kernel, as the device +does not need to take advantage of any of other resources that the +kernel provides. One such common class of devices that are like this are +for industrial I/O cards. + +To address this situation, the userspace I/O system (UIO) was designed. +For typical industrial I/O cards, only a very small kernel module is +needed. The main part of the driver will run in user space. This +simplifies development and reduces the risk of serious bugs within a +kernel module. + +Please note that UIO is not an universal driver interface. Devices that +are already handled well by other kernel subsystems (like networking or +serial or USB) are no candidates for an UIO driver. Hardware that is +ideally suited for an UIO driver fulfills all of the following: + +- The device has memory that can be mapped. The device can be + controlled completely by writing to this memory. + +- The device usually generates interrupts. + +- The device does not fit into one of the standard kernel subsystems. + +Acknowledgments +--------------- + +I'd like to thank Thomas Gleixner and Benedikt Spranger of Linutronix, +who have not only written most of the UIO code, but also helped greatly +writing this HOWTO by giving me all kinds of background information. + +Feedback +-------- + +Find something wrong with this document? (Or perhaps something right?) I +would love to hear from you. Please email me at hjk@hansjkoch.de. + +About UIO +========= + +If you use UIO for your card's driver, here's what you get: + +- only one small kernel module to write and maintain. + +- develop the main part of your driver in user space, with all the + tools and libraries you're used to. + +- bugs in your driver won't crash the kernel. + +- updates of your driver can take place without recompiling the kernel. + +How UIO works +------------- + +Each UIO device is accessed through a device file and several sysfs +attribute files. The device file will be called ``/dev/uio0`` for the +first device, and ``/dev/uio1``, ``/dev/uio2`` and so on for subsequent +devices. + +``/dev/uioX`` is used to access the address space of the card. Just use +:c:func:`mmap()` to access registers or RAM locations of your card. + +Interrupts are handled by reading from ``/dev/uioX``. A blocking +:c:func:`read()` from ``/dev/uioX`` will return as soon as an +interrupt occurs. You can also use :c:func:`select()` on +``/dev/uioX`` to wait for an interrupt. The integer value read from +``/dev/uioX`` represents the total interrupt count. You can use this +number to figure out if you missed some interrupts. + +For some hardware that has more than one interrupt source internally, +but not separate IRQ mask and status registers, there might be +situations where userspace cannot determine what the interrupt source +was if the kernel handler disables them by writing to the chip's IRQ +register. In such a case, the kernel has to disable the IRQ completely +to leave the chip's register untouched. Now the userspace part can +determine the cause of the interrupt, but it cannot re-enable +interrupts. Another cornercase is chips where re-enabling interrupts is +a read-modify-write operation to a combined IRQ status/acknowledge +register. This would be racy if a new interrupt occurred simultaneously. + +To address these problems, UIO also implements a write() function. It is +normally not used and can be ignored for hardware that has only a single +interrupt source or has separate IRQ mask and status registers. If you +need it, however, a write to ``/dev/uioX`` will call the +:c:func:`irqcontrol()` function implemented by the driver. You have +to write a 32-bit value that is usually either 0 or 1 to disable or +enable interrupts. If a driver does not implement +:c:func:`irqcontrol()`, :c:func:`write()` will return with +``-ENOSYS``. + +To handle interrupts properly, your custom kernel module can provide its +own interrupt handler. It will automatically be called by the built-in +handler. + +For cards that don't generate interrupts but need to be polled, there is +the possibility to set up a timer that triggers the interrupt handler at +configurable time intervals. This interrupt simulation is done by +calling :c:func:`uio_event_notify()` from the timer's event +handler. + +Each driver provides attributes that are used to read or write +variables. These attributes are accessible through sysfs files. A custom +kernel driver module can add its own attributes to the device owned by +the uio driver, but not added to the UIO device itself at this time. +This might change in the future if it would be found to be useful. + +The following standard attributes are provided by the UIO framework: + +- ``name``: The name of your device. It is recommended to use the name + of your kernel module for this. + +- ``version``: A version string defined by your driver. This allows the + user space part of your driver to deal with different versions of the + kernel module. + +- ``event``: The total number of interrupts handled by the driver since + the last time the device node was read. + +These attributes appear under the ``/sys/class/uio/uioX`` directory. +Please note that this directory might be a symlink, and not a real +directory. Any userspace code that accesses it must be able to handle +this. + +Each UIO device can make one or more memory regions available for memory +mapping. This is necessary because some industrial I/O cards require +access to more than one PCI memory region in a driver. + +Each mapping has its own directory in sysfs, the first mapping appears +as ``/sys/class/uio/uioX/maps/map0/``. Subsequent mappings create +directories ``map1/``, ``map2/``, and so on. These directories will only +appear if the size of the mapping is not 0. + +Each ``mapX/`` directory contains four read-only files that show +attributes of the memory: + +- ``name``: A string identifier for this mapping. This is optional, the + string can be empty. Drivers can set this to make it easier for + userspace to find the correct mapping. + +- ``addr``: The address of memory that can be mapped. + +- ``size``: The size, in bytes, of the memory pointed to by addr. + +- ``offset``: The offset, in bytes, that has to be added to the pointer + returned by :c:func:`mmap()` to get to the actual device memory. + This is important if the device's memory is not page aligned. + Remember that pointers returned by :c:func:`mmap()` are always + page aligned, so it is good style to always add this offset. + +From userspace, the different mappings are distinguished by adjusting +the ``offset`` parameter of the :c:func:`mmap()` call. To map the +memory of mapping N, you have to use N times the page size as your +offset:: + + offset = N * getpagesize(); + +Sometimes there is hardware with memory-like regions that can not be +mapped with the technique described here, but there are still ways to +access them from userspace. The most common example are x86 ioports. On +x86 systems, userspace can access these ioports using +:c:func:`ioperm()`, :c:func:`iopl()`, :c:func:`inb()`, +:c:func:`outb()`, and similar functions. + +Since these ioport regions can not be mapped, they will not appear under +``/sys/class/uio/uioX/maps/`` like the normal memory described above. +Without information about the port regions a hardware has to offer, it +becomes difficult for the userspace part of the driver to find out which +ports belong to which UIO device. + +To address this situation, the new directory +``/sys/class/uio/uioX/portio/`` was added. It only exists if the driver +wants to pass information about one or more port regions to userspace. +If that is the case, subdirectories named ``port0``, ``port1``, and so +on, will appear underneath ``/sys/class/uio/uioX/portio/``. + +Each ``portX/`` directory contains four read-only files that show name, +start, size, and type of the port region: + +- ``name``: A string identifier for this port region. The string is + optional and can be empty. Drivers can set it to make it easier for + userspace to find a certain port region. + +- ``start``: The first port of this region. + +- ``size``: The number of ports in this region. + +- ``porttype``: A string describing the type of port. + +Writing your own kernel module +============================== + +Please have a look at ``uio_cif.c`` as an example. The following +paragraphs explain the different sections of this file. + +struct uio_info +--------------- + +This structure tells the framework the details of your driver, Some of +the members are required, others are optional. + +- ``const char *name``: Required. The name of your driver as it will + appear in sysfs. I recommend using the name of your module for this. + +- ``const char *version``: Required. This string appears in + ``/sys/class/uio/uioX/version``. + +- ``struct uio_mem mem[ MAX_UIO_MAPS ]``: Required if you have memory + that can be mapped with :c:func:`mmap()`. For each mapping you + need to fill one of the ``uio_mem`` structures. See the description + below for details. + +- ``struct uio_port port[ MAX_UIO_PORTS_REGIONS ]``: Required if you + want to pass information about ioports to userspace. For each port + region you need to fill one of the ``uio_port`` structures. See the + description below for details. + +- ``long irq``: Required. If your hardware generates an interrupt, it's + your modules task to determine the irq number during initialization. + If you don't have a hardware generated interrupt but want to trigger + the interrupt handler in some other way, set ``irq`` to + ``UIO_IRQ_CUSTOM``. If you had no interrupt at all, you could set + ``irq`` to ``UIO_IRQ_NONE``, though this rarely makes sense. + +- ``unsigned long irq_flags``: Required if you've set ``irq`` to a + hardware interrupt number. The flags given here will be used in the + call to :c:func:`request_irq()`. + +- ``int (*mmap)(struct uio_info *info, struct vm_area_struct *vma)``: + Optional. If you need a special :c:func:`mmap()` + function, you can set it here. If this pointer is not NULL, your + :c:func:`mmap()` will be called instead of the built-in one. + +- ``int (*open)(struct uio_info *info, struct inode *inode)``: + Optional. You might want to have your own :c:func:`open()`, + e.g. to enable interrupts only when your device is actually used. + +- ``int (*release)(struct uio_info *info, struct inode *inode)``: + Optional. If you define your own :c:func:`open()`, you will + probably also want a custom :c:func:`release()` function. + +- ``int (*irqcontrol)(struct uio_info *info, s32 irq_on)``: + Optional. If you need to be able to enable or disable interrupts + from userspace by writing to ``/dev/uioX``, you can implement this + function. The parameter ``irq_on`` will be 0 to disable interrupts + and 1 to enable them. + +Usually, your device will have one or more memory regions that can be +mapped to user space. For each region, you have to set up a +``struct uio_mem`` in the ``mem[]`` array. Here's a description of the +fields of ``struct uio_mem``: + +- ``const char *name``: Optional. Set this to help identify the memory + region, it will show up in the corresponding sysfs node. + +- ``int memtype``: Required if the mapping is used. Set this to + ``UIO_MEM_PHYS`` if you you have physical memory on your card to be + mapped. Use ``UIO_MEM_LOGICAL`` for logical memory (e.g. allocated + with :c:func:`kmalloc()`). There's also ``UIO_MEM_VIRTUAL`` for + virtual memory. + +- ``phys_addr_t addr``: Required if the mapping is used. Fill in the + address of your memory block. This address is the one that appears in + sysfs. + +- ``resource_size_t size``: Fill in the size of the memory block that + ``addr`` points to. If ``size`` is zero, the mapping is considered + unused. Note that you *must* initialize ``size`` with zero for all + unused mappings. + +- ``void *internal_addr``: If you have to access this memory region + from within your kernel module, you will want to map it internally by + using something like :c:func:`ioremap()`. Addresses returned by + this function cannot be mapped to user space, so you must not store + it in ``addr``. Use ``internal_addr`` instead to remember such an + address. + +Please do not touch the ``map`` element of ``struct uio_mem``! It is +used by the UIO framework to set up sysfs files for this mapping. Simply +leave it alone. + +Sometimes, your device can have one or more port regions which can not +be mapped to userspace. But if there are other possibilities for +userspace to access these ports, it makes sense to make information +about the ports available in sysfs. For each region, you have to set up +a ``struct uio_port`` in the ``port[]`` array. Here's a description of +the fields of ``struct uio_port``: + +- ``char *porttype``: Required. Set this to one of the predefined + constants. Use ``UIO_PORT_X86`` for the ioports found in x86 + architectures. + +- ``unsigned long start``: Required if the port region is used. Fill in + the number of the first port of this region. + +- ``unsigned long size``: Fill in the number of ports in this region. + If ``size`` is zero, the region is considered unused. Note that you + *must* initialize ``size`` with zero for all unused regions. + +Please do not touch the ``portio`` element of ``struct uio_port``! It is +used internally by the UIO framework to set up sysfs files for this +region. Simply leave it alone. + +Adding an interrupt handler +--------------------------- + +What you need to do in your interrupt handler depends on your hardware +and on how you want to handle it. You should try to keep the amount of +code in your kernel interrupt handler low. If your hardware requires no +action that you *have* to perform after each interrupt, then your +handler can be empty. + +If, on the other hand, your hardware *needs* some action to be performed +after each interrupt, then you *must* do it in your kernel module. Note +that you cannot rely on the userspace part of your driver. Your +userspace program can terminate at any time, possibly leaving your +hardware in a state where proper interrupt handling is still required. + +There might also be applications where you want to read data from your +hardware at each interrupt and buffer it in a piece of kernel memory +you've allocated for that purpose. With this technique you could avoid +loss of data if your userspace program misses an interrupt. + +A note on shared interrupts: Your driver should support interrupt +sharing whenever this is possible. It is possible if and only if your +driver can detect whether your hardware has triggered the interrupt or +not. This is usually done by looking at an interrupt status register. If +your driver sees that the IRQ bit is actually set, it will perform its +actions, and the handler returns IRQ_HANDLED. If the driver detects +that it was not your hardware that caused the interrupt, it will do +nothing and return IRQ_NONE, allowing the kernel to call the next +possible interrupt handler. + +If you decide not to support shared interrupts, your card won't work in +computers with no free interrupts. As this frequently happens on the PC +platform, you can save yourself a lot of trouble by supporting interrupt +sharing. + +Using uio_pdrv for platform devices +----------------------------------- + +In many cases, UIO drivers for platform devices can be handled in a +generic way. In the same place where you define your +``struct platform_device``, you simply also implement your interrupt +handler and fill your ``struct uio_info``. A pointer to this +``struct uio_info`` is then used as ``platform_data`` for your platform +device. + +You also need to set up an array of ``struct resource`` containing +addresses and sizes of your memory mappings. This information is passed +to the driver using the ``.resource`` and ``.num_resources`` elements of +``struct platform_device``. + +You now have to set the ``.name`` element of ``struct platform_device`` +to ``"uio_pdrv"`` to use the generic UIO platform device driver. This +driver will fill the ``mem[]`` array according to the resources given, +and register the device. + +The advantage of this approach is that you only have to edit a file you +need to edit anyway. You do not have to create an extra driver. + +Using uio_pdrv_genirq for platform devices +------------------------------------------ + +Especially in embedded devices, you frequently find chips where the irq +pin is tied to its own dedicated interrupt line. In such cases, where +you can be really sure the interrupt is not shared, we can take the +concept of ``uio_pdrv`` one step further and use a generic interrupt +handler. That's what ``uio_pdrv_genirq`` does. + +The setup for this driver is the same as described above for +``uio_pdrv``, except that you do not implement an interrupt handler. The +``.handler`` element of ``struct uio_info`` must remain ``NULL``. The +``.irq_flags`` element must not contain ``IRQF_SHARED``. + +You will set the ``.name`` element of ``struct platform_device`` to +``"uio_pdrv_genirq"`` to use this driver. + +The generic interrupt handler of ``uio_pdrv_genirq`` will simply disable +the interrupt line using :c:func:`disable_irq_nosync()`. After +doing its work, userspace can reenable the interrupt by writing +0x00000001 to the UIO device file. The driver already implements an +:c:func:`irq_control()` to make this possible, you must not +implement your own. + +Using ``uio_pdrv_genirq`` not only saves a few lines of interrupt +handler code. You also do not need to know anything about the chip's +internal registers to create the kernel part of the driver. All you need +to know is the irq number of the pin the chip is connected to. + +Using uio_dmem_genirq for platform devices +------------------------------------------ + +In addition to statically allocated memory ranges, they may also be a +desire to use dynamically allocated regions in a user space driver. In +particular, being able to access memory made available through the +dma-mapping API, may be particularly useful. The ``uio_dmem_genirq`` +driver provides a way to accomplish this. + +This driver is used in a similar manner to the ``"uio_pdrv_genirq"`` +driver with respect to interrupt configuration and handling. + +Set the ``.name`` element of ``struct platform_device`` to +``"uio_dmem_genirq"`` to use this driver. + +When using this driver, fill in the ``.platform_data`` element of +``struct platform_device``, which is of type +``struct uio_dmem_genirq_pdata`` and which contains the following +elements: + +- ``struct uio_info uioinfo``: The same structure used as the + ``uio_pdrv_genirq`` platform data + +- ``unsigned int *dynamic_region_sizes``: Pointer to list of sizes of + dynamic memory regions to be mapped into user space. + +- ``unsigned int num_dynamic_regions``: Number of elements in + ``dynamic_region_sizes`` array. + +The dynamic regions defined in the platform data will be appended to the +`` mem[] `` array after the platform device resources, which implies +that the total number of static and dynamic memory regions cannot exceed +``MAX_UIO_MAPS``. + +The dynamic memory regions will be allocated when the UIO device file, +``/dev/uioX`` is opened. Similar to static memory resources, the memory +region information for dynamic regions is then visible via sysfs at +``/sys/class/uio/uioX/maps/mapY/*``. The dynamic memory regions will be +freed when the UIO device file is closed. When no processes are holding +the device file open, the address returned to userspace is ~0. + +Writing a driver in userspace +============================= + +Once you have a working kernel module for your hardware, you can write +the userspace part of your driver. You don't need any special libraries, +your driver can be written in any reasonable language, you can use +floating point numbers and so on. In short, you can use all the tools +and libraries you'd normally use for writing a userspace application. + +Getting information about your UIO device +----------------------------------------- + +Information about all UIO devices is available in sysfs. The first thing +you should do in your driver is check ``name`` and ``version`` to make +sure your talking to the right device and that its kernel driver has the +version you expect. + +You should also make sure that the memory mapping you need exists and +has the size you expect. + +There is a tool called ``lsuio`` that lists UIO devices and their +attributes. It is available here: + +http://www.osadl.org/projects/downloads/UIO/user/ + +With ``lsuio`` you can quickly check if your kernel module is loaded and +which attributes it exports. Have a look at the manpage for details. + +The source code of ``lsuio`` can serve as an example for getting +information about an UIO device. The file ``uio_helper.c`` contains a +lot of functions you could use in your userspace driver code. + +mmap() device memory +-------------------- + +After you made sure you've got the right device with the memory mappings +you need, all you have to do is to call :c:func:`mmap()` to map the +device's memory to userspace. + +The parameter ``offset`` of the :c:func:`mmap()` call has a special +meaning for UIO devices: It is used to select which mapping of your +device you want to map. To map the memory of mapping N, you have to use +N times the page size as your offset:: + + offset = N * getpagesize(); + +N starts from zero, so if you've got only one memory range to map, set +``offset = 0``. A drawback of this technique is that memory is always +mapped beginning with its start address. + +Waiting for interrupts +---------------------- + +After you successfully mapped your devices memory, you can access it +like an ordinary array. Usually, you will perform some initialization. +After that, your hardware starts working and will generate an interrupt +as soon as it's finished, has some data available, or needs your +attention because an error occurred. + +``/dev/uioX`` is a read-only file. A :c:func:`read()` will always +block until an interrupt occurs. There is only one legal value for the +``count`` parameter of :c:func:`read()`, and that is the size of a +signed 32 bit integer (4). Any other value for ``count`` causes +:c:func:`read()` to fail. The signed 32 bit integer read is the +interrupt count of your device. If the value is one more than the value +you read the last time, everything is OK. If the difference is greater +than one, you missed interrupts. + +You can also use :c:func:`select()` on ``/dev/uioX``. + +Generic PCI UIO driver +====================== + +The generic driver is a kernel module named uio_pci_generic. It can +work with any device compliant to PCI 2.3 (circa 2002) and any compliant +PCI Express device. Using this, you only need to write the userspace +driver, removing the need to write a hardware-specific kernel module. + +Making the driver recognize the device +-------------------------------------- + +Since the driver does not declare any device ids, it will not get loaded +automatically and will not automatically bind to any devices, you must +load it and allocate id to the driver yourself. For example:: + + modprobe uio_pci_generic + echo "8086 10f5" > /sys/bus/pci/drivers/uio_pci_generic/new_id + +If there already is a hardware specific kernel driver for your device, +the generic driver still won't bind to it, in this case if you want to +use the generic driver (why would you?) you'll have to manually unbind +the hardware specific driver and bind the generic driver, like this:: + + echo -n 0000:00:19.0 > /sys/bus/pci/drivers/e1000e/unbind + echo -n 0000:00:19.0 > /sys/bus/pci/drivers/uio_pci_generic/bind + +You can verify that the device has been bound to the driver by looking +for it in sysfs, for example like the following:: + + ls -l /sys/bus/pci/devices/0000:00:19.0/driver + +Which if successful should print:: + + .../0000:00:19.0/driver -> ../../../bus/pci/drivers/uio_pci_generic + +Note that the generic driver will not bind to old PCI 2.2 devices. If +binding the device failed, run the following command:: + + dmesg + +and look in the output for failure reasons. + +Things to know about uio_pci_generic +------------------------------------ + +Interrupts are handled using the Interrupt Disable bit in the PCI +command register and Interrupt Status bit in the PCI status register. +All devices compliant to PCI 2.3 (circa 2002) and all compliant PCI +Express devices should support these bits. uio_pci_generic detects +this support, and won't bind to devices which do not support the +Interrupt Disable Bit in the command register. + +On each interrupt, uio_pci_generic sets the Interrupt Disable bit. +This prevents the device from generating further interrupts until the +bit is cleared. The userspace driver should clear this bit before +blocking and waiting for more interrupts. + +Writing userspace driver using uio_pci_generic +------------------------------------------------ + +Userspace driver can use pci sysfs interface, or the libpci library that +wraps it, to talk to the device and to re-enable interrupts by writing +to the command register. + +Example code using uio_pci_generic +---------------------------------- + +Here is some sample userspace driver code using uio_pci_generic:: + + #include + #include + #include + #include + #include + #include + #include + + int main() + { + int uiofd; + int configfd; + int err; + int i; + unsigned icount; + unsigned char command_high; + + uiofd = open("/dev/uio0", O_RDONLY); + if (uiofd < 0) { + perror("uio open:"); + return errno; + } + configfd = open("/sys/class/uio/uio0/device/config", O_RDWR); + if (configfd < 0) { + perror("config open:"); + return errno; + } + + /* Read and cache command value */ + err = pread(configfd, &command_high, 1, 5); + if (err != 1) { + perror("command config read:"); + return errno; + } + command_high &= ~0x4; + + for(i = 0;; ++i) { + /* Print out a message, for debugging. */ + if (i == 0) + fprintf(stderr, "Started uio test driver.\n"); + else + fprintf(stderr, "Interrupts: %d\n", icount); + + /****************************************/ + /* Here we got an interrupt from the + device. Do something to it. */ + /****************************************/ + + /* Re-enable interrupts. */ + err = pwrite(configfd, &command_high, 1, 5); + if (err != 1) { + perror("config write:"); + break; + } + + /* Wait for next interrupt. */ + err = read(uiofd, &icount, 4); + if (err != 4) { + perror("uio read:"); + break; + } + + } + return errno; + } + +Generic Hyper-V UIO driver +========================== + +The generic driver is a kernel module named uio_hv_generic. It +supports devices on the Hyper-V VMBus similar to uio_pci_generic on +PCI bus. + +Making the driver recognize the device +-------------------------------------- + +Since the driver does not declare any device GUID's, it will not get +loaded automatically and will not automatically bind to any devices, you +must load it and allocate id to the driver yourself. For example, to use +the network device GUID:: + + modprobe uio_hv_generic + echo "f8615163-df3e-46c5-913f-f2d2f965ed0e" > /sys/bus/vmbus/drivers/uio_hv_generic/new_id + +If there already is a hardware specific kernel driver for the device, +the generic driver still won't bind to it, in this case if you want to +use the generic driver (why would you?) you'll have to manually unbind +the hardware specific driver and bind the generic driver, like this:: + + echo -n vmbus-ed963694-e847-4b2a-85af-bc9cfc11d6f3 > /sys/bus/vmbus/drivers/hv_netvsc/unbind + echo -n vmbus-ed963694-e847-4b2a-85af-bc9cfc11d6f3 > /sys/bus/vmbus/drivers/uio_hv_generic/bind + +You can verify that the device has been bound to the driver by looking +for it in sysfs, for example like the following:: + + ls -l /sys/bus/vmbus/devices/vmbus-ed963694-e847-4b2a-85af-bc9cfc11d6f3/driver + +Which if successful should print:: + + .../vmbus-ed963694-e847-4b2a-85af-bc9cfc11d6f3/driver -> ../../../bus/vmbus/drivers/uio_hv_generic + +Things to know about uio_hv_generic +----------------------------------- + +On each interrupt, uio_hv_generic sets the Interrupt Disable bit. This +prevents the device from generating further interrupts until the bit is +cleared. The userspace driver should clear this bit before blocking and +waiting for more interrupts. + +Further information +=================== + +- `OSADL homepage. `_ + +- `Linutronix homepage. `_ diff --git a/MAINTAINERS b/MAINTAINERS index c36976d..3294c14 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -12965,7 +12965,7 @@ USERSPACE I/O (UIO) M: Greg Kroah-Hartman S: Maintained T: git git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git -F: Documentation/DocBook/uio-howto.tmpl +F: Documentation/driver-api/uio-howto.rst F: drivers/uio/ F: include/linux/uio*.h -- 2.1.4