I started to write linux driver and i am confident on it now, but my interest now is to write
lower-level driver (platform driver) for spi or USB or i2c controller. Is there any i can start writing to practice platform driver on linux PC. Can some suggest how to start writing platform driver on linux.
Thank you
A good way is to look at the existing drivers, look at the list of open bugs and start to fix them. That will give you a good introduction to the kernel, you will learn to work as part of a huge, distributed team (will look good on your CV) and you will help to make the world better, one line of code at a time.
The next step is then to find some unknown, unsupported hardware and write a driver for it. The start here is to copy an existing driver or extend it (depending on how "different" the hardware is).
Related
I'm new to device drivers in Linux. And my first day task is to debug driver using GDB in Linux.
I need to debug some XYZ (PCIe device driver supports ethernet) device driver to know about the flow and what is going on device's registers and all.
I have installed the driver with patch file and insmod command.
The device is working properly. But am not getting any solution to debug the device driver.
All I know is that how to debug C program using GDB in Linux(fedora20). I got one link similar to my Problem but from that also I have not got any knowledge.
Can anybody please share your thoughts that how can I start from scratch.
I am very specific to learn about Debugging device drivers in Linux. Especially that init or probe function inside my driver I need to know the flow.
The gdb debugger is useful to debug user-space application level programs (since it uses ptrace(2)).
For kernel code, things are different. Consider using kgdb (I don't know the details). You might also add debug prints ....
I recommend at least reading more about operating systems, e.g. Operating Systems: Three Easy Pieces (freely downloadable), and reading something about Linux programming (perhaps the old ALP, and also intro(2), syscalls(2) and related stuff). Don't dare coding Linux loadable kernel modules without good familiarity with Linux programming (in user-land). See also kernelnewbies.
BTW, you should prefer writing user-land code than kernel modules. A very simple rule of thumb is to avoid writing kernel code when possible.
To begin with, you may need to understand basics of device driver and kernel in linux. Subsequently focus as per the type of driver in-hand. You also need to understand the functionality (specification / manual / datasheet) of the device you are working on.
The very basic approach for debugging can be using printk. Normally there will be debug logs that can be enabled through compilation flags. If it is present, enable it so that it can give important pointers else you might need to add it on your own.
Start with verification of driver registration and verification of loading of your driver (static or loadable module as per your requirement). Check whether it is getting listed as part of sysfs or proc as applicable. Check whether probe is successful and subsequently the appropriate read/write/open/close/other calls as per your driver / device functionality.
The dmesg shall be very helpfull for viewing the kernel messages. There are also tools like kdb, LTT, strace that can be useful as per the scenario.
I have USB oscilloscope Velleman PCSU 1000 which is Windows-only, and I'm thinking of ways to make it work in Linux.
I've come across interesting publication on driver reverse-engineering, so, at least in theory, I can reverse-engineer the driver for the oscilloscope, and then write Linux driver for it. But I have no idea how to make their proprietary software work in Wine with my new driver? Is it possible?
If not, then it seems I have only one option: write not only the driver, but reimplement the software as well. This is awful amount of work, unfortunately.
And, as far as I know, there is no common device class for this kind of devices, so I can't write some generic driver to make any other similar software work with the oscilloscope. Right?
Anyway, any suggestions and ideas are highly appreciated.
Context
Debian 64 bit. kernel 3.18.x
Litterally struggling to understand how a network driver is initialized.
I mean how to choose which flag to set. I dig in the kernel for days now to train myself. The card setup is the only point I miss.
I take the intel 82574 as an example. I downloaded the card's datasheet, saw many information but not a clue on how to setup the hardware.
Question
Where to start to know what flags to set ? The datasheet didn't helped me (i am not very experienced but willing to learn).
Please give me a starting point, a tip or anything to help me understand what is going on in the already written open sourced driver.
How can a developer knows how to initialize his nic ? (yes reinventing the wheel the time to understand)
You'll need to read the source code of the kernel module that handles your specific NIC.
EDIT: Of course, to develop such a module, you'd usually just use a register map as specified in a data sheet or application node; often, manufacturers develop their linux drivers themselves, so the driver developers might even be the same people that developed the chipset (because it's really handy to have a platform to test against -- it's impossible to test hardware without having something like a driver, so you might as well write a proper driver).
Furthermore, devices often come with code examples -- no one is going to build a device based on an IC that he has not seen in action.
If you've got access to neither proper documentation nor source, you can only reverse engineer - and that's an incredibly large field.
Using your example with the Intel 82574 Network Adapter, Intel provides a zip file of the source code used to build the Linux driver. The driver is like all drivers in that it hooks into the OS API for Networking.
The Linux networking API is document on both the linux.org site and discussed on popular Linux sites like lwn.org. Below is the link to lwn's chapter on Network drivers using the networking API called NAPI.
https://static.lwn.net/images/pdf/LDD3/ch17.pdf
You'll notice in the Intel igb driver source code that the NAPI net_device data structure is one of the first things that is setup. It registers the driver with the OS. This way the OS knows which igb functions to call when loading/unloading the driver, or when needing to send/receive data.
The igb functions read/modify/write the necessary bits in the 82574's memory-mapped registers that control and monitor the device. The device registers are all documented in the 82574 datasheet available on Intel's site. And this is usually the case for almost any networking company like Broadcom/Chelsio/Mellanox/Marvell.
Hope that helps a little more.
I have buy an usb video grabber on ebay but I haven't received an official device, it's a fake, and this one is the only one fake not supported by Linux. I would like to write the linux driver, but I have no knowledge on driver dev. Where can I find tutorial for driver dev learning on linux?
The device is an easycap dc60++, identified as fushicai usbtv007. More details here : http://linuxtv.org/wiki/index.php/Easycap#Known_Easycap_devices
It works on win7, so I can easily sniff usb protocol.
Thanks you in advance
IMHO, the best way to learn how to develop drivers for the kernel is to take an existing driver (best if it's from mainline) that is similar to what you want and look at how they're doing it. For function references, head to your favourite LXR site and search it up.
You could look up Linux driver development on Google and find some tutorials but I wouldn't recommend it for anything other than to get started since they're likely to be outdated or use deprecated kernel APIs.
Otherwise, there's always libusb if you don't want to get into the world of kernel driver development.
Good luck.
I made an experimental userspace driver for this device:
https://github.com/memeruiz/usbtv007
Hopefully somebody (or me) will take this and make a proper kernel driver for it.
I've made a driver for the device in question (https://lkml.org/lkml/2013/6/10/381). There's a big space for improvement and I'd be very glad if you could get involved.
The following documentation is helpful:
Linux Device Driver, third edition, book.
PDFs: http://lwn.net/Kernel/LDD3/
epub: http://v3.sk/~lkundrak/ldd3/
Video4Linux2 API: http://lwn.net/Articles/203924/
Videobuf2 API: http://lwn.net/Articles/447435/
When it comes to a good example, have a look at the drivers/media/usb tree, particularly the stk1160 driver.
I didn't yet have a look at Federico Ruiz's libusb driver for the device, but it seems he mostly figured out the same things as I did about the hardware. I suggest you take a look at it though, as I'll certainly do.
Also, linux-media list is probably a better place to ask questions like this. I've got here mostly by accident and there certainly are much more capable people on the list.
Have a great day!
I have a Linux network driver that was originally written for 2.4 kernel. It works perfect.
I want to port it to kernel 2.6.31 and then to ARM Linux with same kernel i.e. 2.6.31. I have actually done some minor changes to the driver so that it is able to compile under kernel 2.6.31 and it also loads and unloads without crashing. It also cross compiles for the ARM Linux. But I am unable to test it on ARM so far.
How do I check that the driver is fully compatible with the target kernel, and what considerations shall be made to make it compatible with ARM.
The driver is a virtual network device driver.
Thanks in advance.
Maybe you could use Qemu ( http://wiki.qemu.org/Main_Page) to emulate an ARM platform to be able to test your driver.
You cannot check the driver like that - you have to consider the API changes within 2.6.x series kernel. The changes are quite significant and the overall of the API's from the 2.4 series which is not currently in use.
I would suggest you to go here to the Amazon book store for this book in particular. The book is called 'Essential Linux Device Drivers', by Sreekrishnan Venkateswaran. A very well detailed explanation that will be your guidance in ensuring it works properly.
Since you mentioned the device driver is a network, presumably char device (You're not accessing it in blocks), well, the good news is that the 2.6.x series kernel APIs for the character devices are significantly easier and more centralized to focus on - in fact a lot of the framework is already in place in which the author of said book explains very clearly.
By the way, the book focusses on the latter 2.6.x series after 2.6.19, so this will help you clue in on what needs to be done to ensure your driver works.
You did not specify the ARM chipset you're targetting?
As for testing... well.. perhaps the best way to do this, this is dependant on how you answer the above question to you regarding ARM chipset - if its ARMv6, then perhaps, a cheap android handset that you can easily unlock and root, and pop the kernel in there and see what happens - sorry for sounding contrived but that's the best thing I can think of and that's what pops into my head, to enable you to test it out for ease of testing :)
PS: A lot of cheap ARMv6 handsets would have kernel 2.6.32 running Froyo if that's of any help!