Uio driver .h

So, on a system with byte pages, the first memory area will be found with an offset of zero, the second at , the third at , etc. Once that is figured out, though, everything is pretty straightforward. There are some limitations, of course. UIO drivers are char drivers; there is no provision for creating user-space block or network drivers at this time.

It is not possible to set up DMA operations from user space. The patch set includes an example driver to show how it all works. According to Thomas Gleixner , the original, fully in-kernel version of the driver had to implement 68 different ioctl commands and was over 5, lines long.

The associated user-space code was over 3, lines as well. The new driver eliminates all of that, with a total of lines of kernel code and just under 3, lines in user space. Andrew Morton has expressed some reservations about the patch: I'm a bit uncertain about the whole UIO idea, really. I have this vague feeling that we'd prefer to encourage people to move device drivers into GPL'ed kernel rather than encouraging them to do closed-source userspace implementations which will probably end up being slower, less reliable and unavailable on various architectures, distros, etc The authors respond that it's not really about doing proprietary drivers, though some of that will undoubtedly go on.

There's a number of people, especially in the embedded space, who want to do user-space drivers, for prototyping purposes if nothing else. The UIO framework gives them a relatively safe and standard way to write these drivers, which is seen as being better than having them each create their own kernel hooks. The patch has not been merged as of this writing, but, unless stronger objections arise, it's chances of getting into 2.

This dangerously seems like an atempt to be able to create proprietary drivers and bypass the GPL. On one hand I understand the good of having user-space drivers, but on the the other hand I don't see how that can be done and not create this loophole.

It depends on if your goal is to write an excellent, open OS kernel or to force all software in the world to become GPL. The kind of user-space drivers people were doing don't compare with the drivers you will be able to do, even if you probably can't do a user-space graphics driver. Other than that, I don't have problems running the nvidia drivers at my home PC the few games I still play need 3D. Now if the law were applied SAMBA doesn't count as it is explicitly a copy of the windows API as such the license of the kernel is irrelevant for UIO simply because it is userspace and is using the defined interface.

The Samsung monstrosity recently covered by LWN is one such example. This issue concerns me too. On one hand, I'd prefer a closed source driver to no driver much of the time. On the other hand, if it's a bad driver it's not much better than no driver at all, and lacking the ability to fix or debug it because it's just a binary blob would be seriously annoying.

Set this to one of the predefined constants. Fill in the number of the first port of this region. If size is zero, the region is considered unused. Note that you must initialize size with zero for all unused regions. It is used internally by the UIO framework to set up sysfs files for this region.

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.

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. As this frequently happens on the PC platform, you can save yourself a lot of trouble by supporting interrupt sharing.

In many cases, UIO drivers for platform devices can be handled in a generic way. 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. You now have to set the. 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.

Especially in embedded devices, you frequently find chips where the irq pin is tied to its own dedicated interrupt line. You will set the. After doing its work, userspace can reenable the interrupt by writing 0x to the UIO device file. All you need to know is the irq number of the pin the chip is connected to. To set a custom name, a property named "linux,uio-name" may be specified in the DT node. 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. Set the. When using this driver, fill in the. The dynamic memory regions will be freed when the UIO device file is closed. Once you have a working kernel module for your hardware, you can write the userspace part of your driver. Information about all UIO devices is available in sysfs. There is a tool called lsuio that lists UIO devices and their attributes. It is available here:.

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 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. A drawback of this technique is that memory is always mapped beginning with its start address.

After you successfully mapped your devices memory, you can access it like an ordinary array. Usually, you will perform some initialization. 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. The file descriptor can be passed to poll. The memory areas described by the kernel-space driver can be mapped into user space with the mmap call.

The interface is just a little strange: the offset value passed to mmap should be N times the page size for the N th memory area.

So, on a system with byte pages, the first memory area will be found with an offset of zero, the second at , the third at , etc. Once that is figured out, though, everything is pretty straightforward. There are some limitations, of course.

UIO drivers are char drivers; there is no provision for creating user-space block or network drivers at this time. It is not possible to set up DMA operations from user space. The patch set includes an example driver to show how it all works. According to Thomas Gleixner , the original, fully in-kernel version of the driver had to implement 68 different ioctl commands and was over 5, lines long.

The associated user-space code was over 3, lines as well. The new driver eliminates all of that, with a total of lines of kernel code and just under 3, lines in user space. Andrew Morton has expressed some reservations about the patch:. The authors respond that it's not really about doing proprietary drivers, though some of that will undoubtedly go on. There's a number of people, especially in the embedded space, who want to do user-space drivers, for prototyping purposes if nothing else.