On Fri, Apr 20, 2018 at 03:51:42PM +0300, Alper Yazar wrote:
> Hi,
>
> I am trying to communicate a custom PCIe device in Linux. I didn't
> have experience on programming with using system calls and writing
> Linux device drivers.
>
> I loaded uio_pci_generic driver for the device and /dev/uio0 was
> generated as character device. Then I wrote the following C program to
> dump 128K data from the device to a file. The device has only BAR0
> with size 128K.
...
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <sys/mman.h>
> #include <stdio.h>
>
> #define MMBLOCK_SIZE (1024*128)
> #define PCI_FILE "/dev/uio0"
> #define BIN_FILE "dump.bin"
>
> int main() {
>
> int f;
> FILE * fdumpptr;
> char *ptr;
>
> printf("PCI FILE: %s\n", PCI_FILE);
> printf("BIN FILE: %s\n", BIN_FILE);
>
> f = open(PCI_FILE, O_RDWR);
>
> fdumpptr = fopen("dump.bin","w");
>
> if(NULL == fdumpptr)
> {
> perror("Can't open BIN FILE");
> return 1;
> }
>
> if(-1 == f)
> {
> perror("Can't open PCI FILE");
> return 1;
> }
> else
> {
> printf("PCI FILE opened successfully\n");
> }
>
> ptr = mmap(NULL, MMBLOCK_SIZE, PROT_READ, MAP_SHARED, f, 0);
>
> if (MAP_FAILED == ptr)
> {
> perror("Can't do memory map on PCI FILE");
> return 1;
> }
> else
> {
> printf("memory map succesfull\n");
> }
>
> if (MMBLOCK_SIZE == fwrite(ptr, 1, MMBLOCK_SIZE, fdumpptr))
> {
> printf("Content dumpped succesffully\n");
> }
> else
> {
> printf("Can't write dump file\n");
> return 1;
> }
>
> return 0;
> }
>
> However `mmap()` returned `MAP_FAILED`. If I access to device using
> sysFS by changing `#define PCI_FILE
> "/sys/bus/pci/devices/0000:08:00.0/resource0"` everything works.
I think that's expected.
> So as far as I understood, I could mmap() the /dev/uio0 device but it
> gives an error. errno is 22 after failed mmap() call which corresponds
> to "Invalid argument". Is it possible to mmap() character device? What
> would be the problem?
Right but which BAR would we map? A generic device can have up to 6 of these.
For this reason uio pci generic just doesn't support mmap - you are
supposed to mmap the correct BAR through sysfs.
> Nothing happens in dmesg when I modprobe uio_pci_generic, relate my
> major and minor number with the driver, run the working or non working
> code.
>
> There is no `maps` directory under `/sys/class/uio/ui0/`. Is this a
> problem indicator?
It's not a problem I think - we could add these as the driver is generic
using a minimal interface was deemed best for security. So just follow
the device link to get at the BAR:
/sys/class/uio/ui0/device/resource0
and mmap that.
--
MST
