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Having a problem logging in? Please visit to clear all LQ-related cookies. Introduction to Linux - A Hands on Guide This guide was created as an overview of the Linux Operating System, geared toward new users as an exploration tour and getting started guide, with exercises at the end of each chapter.
For more advanced trainees it can be a desktop reference, and a collection of the base knowledge needed to proceed with system and network administration. This book contains many real life examples derived from the author's experience as a Linux system and network administrator, trainer and consultant. They hope these examples will help you to get a better understanding of the Linux system and that you feel encouraged to try out things on your own. To receive this Complete Guide absolutely free. Hello all, I am new in the Forum and this is my first post! I would like to say that I have used this Forum in the past and that there is very useful information.
I am a software engineer with experience developing Linux device drivers (USB 2.0). I used the usb-skeleton template by Greg Kroah-Hartman, which was of great help. I need to develop now a device driver for a PCI express board: the Xilinx Virtex-5 LXT/SXT and I am a little bit lost. I know nothing about PCIe. So my first question is: Is there a similar template for PCIe to start with? Any advice would be more than welcome! Happy Christmas!
Hi magda, I'm an electrical engineer an I don't know a lot of thing about the inside of the linux kernel and how to make device drivers. But, me too I am trying to develop a PCI express device driver for Xilinx Virtex-5 SXT. I was reading books 'Linux Device Drivers' and 'PCI Express system architecture' but I don't think there is enough info in these book to do that. I will firstly try to make an USB driver (If you use ML-506 evaluation board or equivalent there is already an USB device port.) If you have any more info about pci express let me know. Hi, here you have links to pci skeletons that I've found useful, from the simplest to the most complicated: Linux Device Drivers is quite complete boot, just follow chapter 9 and edit pciskel.c (first of the previous links) accordingly in order to get simple read and write operations. Also you need to decide if you want your driver to be a Character or a Block device, here you have some discussions: In case you go for Character Device then you will need to create it from a linux terminal. I don´t have the info on how to do that yet.
I hope this helps, Magda. You are welcome, I am glad the info was useful. Let me know if you have any problem.
Magda Dear All, First, Thank u very much for this great discussion, I am new for PCI driver development, I write a simple PCI driver and I need to test it, in other words I need to do simple read/write/ioctl operations, but I have no hardware(PCI development board) for doing this, I tried to use any of the PCI cards connected to my PC, I understand that,to invoke the Driver probe method, the VEDNERID and DEVICEID of my driver should match one of the IDs of the cards connected to PC, so I used the lspci utility to list all vendor and device IDs. And I used one of these IDs in my code to make the kernel invoke my driver probe method, inside the probe, I tried to get the address of BAR0 and BAR1 using pciresourcestart to allocate my data structure in BAR0 of the PCI, but It fails and returns NULL from pciresourcestart.
My question: Does anyone know how I could fix this problem?? Appreciate your help Thanks Regards Mahmoud. I did manage to get something running. Andromede 5 cracks. I can get the basic stuff up and running but am having some problems with the status bit handling in the DMA address space mapped in kernel for the fpga. Will have to look more into that. I had used the links which magda posted and got a.tar files somewhere from the forums which had driver code which implemented something similar to this. I will try to search for it and will see if i can find it.
Let me post my source file for the driver. Hope this helps. Hi, here you have links to pci skeletons that I've found useful, from the simplest to the most complicated: (.) Linux Device Drivers is quite complete boot, just follow chapter 9 and edit pciskel.c (first of the previous links) accordingly in order to get simple read and write operations. Also you need to decide if you want your driver to be a Character or a Block device, here you have some discussions: (.) In case you go for Character Device then you will need to create it from a linux terminal. I don´t have the info on how to do that yet. I hope this helps, Magda Hi.
I kinda need to do the same thing as you. Develop a device driver for a PCI express board: the Xilinx Virtex-5 LXT. But I'm kind stuck on this.
I'm looking into the books referred in topics and I've now started taking a look at the example codes posted here. Even so I didn't manage to get anything running yet. Did you manage to get this working? Thanks in advance.
Best regards. I kinda need to do the same thing as you. Develop a device driver for a PCI express board: the Xilinx Virtex-5 LXT.
But I'm kind stuck on this. I'm looking into the books referred in topics and I've now started taking a look at the example codes posted here. Even so I didn't manage to get anything running yet. Did you manage to get this working? Thanks in advance.
Best regards. I was in a similar situation as you are in, a few months ago; In general, in your driver you must enable PCI/PCI-Express device, initialize it and all its features need to be initialized for operation, provide access method/s to it and in from here comes special section that depends on your hardware internal architecture that you provide by programming FPGA. I started with ldd3, Linux essential device drivers, and some kernel development knowledge. Now that the device is getting ready to operate, I've developed driver as well in an incremental manner in parallel with device.
I've provided access to device from user space through a character device node in File System (for testing device functionality) and, access from kernel space from kernel crypto api. Please give more description about your current status, errors you are involve and device architecture and functionality. I'll be pleased if I could help you. Hi Friends, I want to use Linux terminal or console in order to communicate other system which is connected with PCI Express bus. I dont know how to make this. I have Linux PC which is connected to PowerPc We usually use ssh in order to communicate or access power pc by which are connected with Ethernet cable. I need to make similar stuff but both the PC's are connected with PCI Express Bus.
Do i need to make any changes in PCI Express driver in order to do this? Can anyone please help me how to do this!!
I am working on development board for one of our FPGA designs prior to the arrival of actual hardware (and a driver from our customer). I'm one of FPGA designers on the project and I have no experience writing a PCI or PCIe driver.
I'm supposed to be developing the driver against CentOS 7.3 (Linux Kernel version 3.10 + patches). The driver needs to be able to set aside a portion of memory for DMA accesses by the FPGA, and to perform single word 32-bit read and write operations. I've done some Googling and asking around at work, and I found the examples from Linux Device Drivers 3rd Edition from O'Reilly Media.
However, it's extremely dated (13 years old) and I'm not sure how much of it still applies to a modern kernel. And I don't have access to the book to see if it's worth a read.
Apart from that, I've found a few random pages online that don't really do anything other than to explain how to identify a PCI/PCIe device. Every time they talk about actually interacting with the device, they don't explain a single thing so I see some code on a website with no real explanation. So my question to the community is: does anyone know of a good, somewhat comprehensive resource or well commented example of a PCIe driver (or drivers) that would somewhat do what I need it to do (DMA and single word reads and writes). I'm a big fan of doing things the easy way and get up and running before doing things the right way. Also it's hard to say exactly what the right way is without knowing a lot of your requirements. First, search 'uio driver'.
Assuming your kernel supports it, it's a super easy way to get something working. There's loads of simple examples online of how to set it up. Set aside a portion of memory for DMA accesses For prototyping, you might be able to get away with just booting up with less memory. LDD discusses this. Perform single word 32-bit read and write operations If you got your UIO driver to bind to your device then you should be able to mmap the device to get access to it's memory. For prototyping, you might be able to get away with just booting up with less memory. LDD discusses this.
I should have been more specific. I need to set aside a portion of processor memory for DMA accesses from the FPGA. I only need 100 MB region for the application which is more than achievable on my development system system. The device in question is a software controlled switch-like product that uses a processor for certain tasks.
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I don't need, or care, to test those tasks other than to confirm that DMAs work appropriately at this time. Also, thanks for telling me about UIO Drivers. I've been reading about them and they might be the easiest way for me to get this up and running. The only problem is that I don't see a clear way of using the UIO Driver in the kernel tree that has DMA support as I don't think anyone has actually documented how you access the DMA region. So because of memory fragmentation, there may not be 100MB of contiguous memory on your system.
In practice, I've seen my systems fail above 4MB. From LDD chapter 15 but high-order requests are prone to fail even when the requested buffer is far less than 128 KB, because system memory becomes fragmented over time. There's a bunch of random details that I'm hazy on like whether it's low memory or high memory, and I think there's this contiguous memory allocator (CMA) framework now that allows you to kick out anything that is in your range when you allocate it.
I haven't actually done it, but someone was explaining it all to me a while ago. Here's the bit about the boot argument.
Reserving the top of RAM is accomplished by passing a mem= argument to the kernel at boot time. For example, if you have 256 MB, the argument mem=255M keeps the kernel from using the top megabyte. I do this part all of the time. I also used 'cat /proc/iomem' to see where all of my physical addresses are.
I think you are overcomplicating this, which is why it seems over complicated. Interacting with a PCI/e device is very simple from the kernel's perspective.
Pretty much nothing has changed in terms of PCI which is why it's so great to work with. From the kernels perspective, PCI and PCIe are the same thing.
So you can use them interchangeably in this context. Secondly, from the perspective of the kernel, PCI devices are just 'memory'. There are three types of memory, config memory, register memory (aka programmed I/O or PIO memory) and DMA memory. When you write to config/PIO memory, the PIC bridge will generate read/write TLPs on behalf of the CPU (and in the case of non-cached reads cause the CPU to effectively halt waiting for the result).
In the case of DMA memory, nothing happens, it's simply a region of regular memory that your software can read/write to/from, but the device can also read to/from. Typically, a PCI device will operate something like this: 1) find the PCIe device that you are planning to work with based on the device type and ID (that is stored in the config memory region). 2) retrieve the base address register (BAR) from the config memory which points to a memory mapped region where your register map will reside (PIO memory). 3) Allocate DMA'able memory inside of the kernel.
4) Pass that allocation down to the device via the register map/ PIO memory. 5) Read from/write to the DMA memory region. 6) Trigger DMA send/receive operations by ringing a 'doorbell' register in your register map.
For the sake of argument, I'll use this open source driver as an example (because I know it.), but they are pretty much all the same. First thing with all drivers is there is an 'init'ialization function and an 'exit' function. You can find them down at line 1672. The driver then registers to be a PCI driver, and supplies some basic functions (line 1690).
Those functions are described in the structure, struct pcidriver, and are probe (what happens when a new device is added), remove (what happens when a device is unplugged e.g hotplug or driver shut down) and shutdown (what happens when a device is shut down). The probe function is the most important for getting started. In the first few lines, the function does some house keeping and then does a pcienabledevicemem which gets access to the config area, and then a bunch of pretty much boiler plate code to find and map the register space memory region. The final piece of which happens on line 903/904 where the memory mapped region is converted from a physical address into a kernel virtual address, and then the driver starts accessing registers on the next substantive line (917).
From this point onwards the driver does lots of internal stuff relevant to the device (figuring out which version, how many ports etc, etc). At line 1090 we pick up again with DMA getting set up. The driver first checks if the card is in 64bit DMA mode or 32 bit (this driver only works with 64bit).
And it sets the DMA mask accordingly. And that's pretty much it for the probe function. Now, you could do the rest of the DMA set up here, but in this case, the device is a network card and so it implements the 'netdev' kernel interface, so the DMA allocation happens when an application opens a new socket. Setting up the netdev happens on line 1449 and calls into line 1403 in exanic-netdev.c. This function does a lot of setup, but the important line is 1458 registernetdev. This basically sets up an 'eth0' interface which things like 'ifconfig' will now recognise. It has the same kind of structure as a PCIe device, a struct, populated with a bunch of functions derived from line 933 (static struct netdeviceops exanicndos).
The crucial function here is exanicnetdevopen. This is called when an application tries to open a socket to speak to the network and it's where the final piece of the DMA puzzle happens. On line 629, the function calls exanicallocrxdma which eventually calls virtregion = dmaalloccoherent which is where the DMA memory gets allocated and on line 215 is assigned to a port on the card which get's written into the register space, which the card can now use. Unfortunately, the reality of a real driver is slightly more complicated than the theory, but hopefully this should give you a good idea of the pieces you need to assemble to get working what you need to. This could either be a nightmare or pretty simple. Depending on what already exists. Step one, you've got a specific kernel version to use.
Linux Pcie Driver Code Example
Fine, can you compile it? Does it boot? Do you have terminal access? Step two, what does the dev board's creator provide? Normally if a board is designed to run linux, they'll have some sort of kernel repository, and documentation.
This should have a PCIe driver included. Try building this and demo apps, and seeing if it works. Step three, merge the two kernels / convince your work to just use the provided kernel repository.
This will be pretty simple if the kernel's are similar versions. If not, then you'll have to do lots of googling on linux kernel driver calls. In general, somebody has already done something similar. Copy that and make any necessary mods. The FPGA doesn't run Linux, the PC it's in runs Linux and that's where I need to create a driver.
The dev board's creator, Altera/Intel PSG, can best be described as seriously lacking in documentation department. Despite this card having a PCIe edge connector, Altera never created an example driver because they only used the a generic Windows drivers which they configure in their test tool (which only runs under Windows, because of course it does). They do have an example driver available for one of their other boards, but it isn't useful for our use case (it's an OpenCL driver and doesn't provide easy, direct access to internal registers). In my work we have a few boards that have a CPU of some type that runs linux and an FPGA that communicate over PCIe, so I kind of assumed you'd be in the same state. Plus after a bit of thought, I think I was on the wrong track. I was assuming you wanted to know how to talk to the PCIe peripheral on your processor.
Which you totally don't need to do (if you were thinking that). You just need to interface with the PCIe comms layer of linux. Which unfortunately I don't have any suggestions, other than find an existing driver and copy it with any relevant changes. This looks interesting. That's fair enough. We have other engineers who tend to work on designs with embedded processors.
I typically only use very tiny processors to handle tasks that aren't time critical and would otherwise consume a lot of LUTs implemented in HDL when I need to do so. I mostly focus on FPGA system level design and high speed data paths and controls. Thanks for that link though. I've been trying to make sense of all the poorly documented resources that people have told me about and that I've found (I found that same link early today). I'm inundated with information and not many good explanations at a high level overview level, sadly. But I think that's just a general problem with driver development.
Yeah pretty much. Linux drivers are generally a bit high level for me.
I'm more a micro processor sort of guy, but I've dabbled. I still have no idea how to write a driver from scratch, despite having done it a few times. It's mostly find something similar, and then mod it until it works. Start with the driver registration code. It'll be somethinginit or similar.
It'll call something like xxxdriverregister, passing a struct with some function pointers. One of those functions will be something called xxxprobe. The init method gets called first, it tells the kernel your driver exists, and what hardware / other driver it matches with. When the kernel finds that bit of hardware it then calls your probe function, which configures things as you want (memory access, dmas, interrupts, user space interface (through sysfs or ioctl calls), timers.). Then you just fill in the blanks. Such as if you've connected the driver to user space through sysfs then handling people opening, reading and writing the relevant files. Or if you've connected through ioctl calls, then handling that call, parsing what the request is and implementing it.
The above is a very very basic overview of a general kernel driver, but it might give you somewhere to start trying to understand things. Just find any PCIe driver that does roughly what you want, and google for any function calls, starting with the init function, and then the probe function.