AXI_DMA device driver for Linux

Hi Silviu,
I use VDMA IP. I try to use exactly same driver, but without succeed. I dont know how to use it. I found information about xvdma.c driver (http://forums.xilinx.com/t5/Embedded-Linux/Xvdma-Driver/td-p/279964) who works as bridge between base VDMA kernel driver and user application, but I am not able to colmpile it. I spent 2 days without succeed.
My final solution is easy. I use mmap to access VDMA IP registers and program it. I have working solution after 2 hours.

Linux is little hell. :-)

Hi Vatu,
Can you please share the code that uses mmap to control the driver from user space?

Thank you,
Silviu

Hi Vatu,
In my case AXI DMA is at 0x40400000 but
mmap() needs a file descriptor, fd.
How do you create this fd if there is only a physical address that I need to access?
Can fd be NULL?
Does it mean that there must be a driver running already?
Do I need to configure the device-tree file before I use the mmap()?

Hi Silviu,
hete is my solution http://www.arbot.cz/post/2013/03/20/VDMA-on-ZedBoard.aspx.

Hi Silviu,
you can use fd=open("/dev/mem", O_RDWR) to get file descriptor.
Function mmap maps physical addres to virtual adress space.

mmap(NULL, <length>, PROT_READ | PROT_WRITE, MAP_SHARED, fd, <physical adress>);

This solution access directly to VDMA IP registers, therefore you does not need any driver.

You does not need instantiate any driver in device-tree, but is good idea to limit memory used by kernel to reserve physical memory for store data by DMA engine.

Thanks, I spent more time reading a device driver book and I got to the same conclusion. The quick way to drive and get data from the AXI-DMA device is with mmap function. After that is like a bare metal driver.

Another interesting way is to implement a small character driver that redefines the mmap to map it to a physical address. In theory you can use kmalloc() convert its return address to physical address with virt_to_phys().
But I get a fragmentation issue  when using kmalloc().

Thanks for your help,
Silviu

Thanks, it helps a lot.

Silviu

Hi Vatu,
How do you invalidate the cache for one of your mmap regions?

Thanks,
Silviu

Hi Silviu,
I have not yet figured out.
One option is use ACP.

Functional solution is interesting for me.

Vatu

Hi Vatu,
A user space driver is like this:

int dma_initUser(DmaDevId_t devid, XAxiDma_User_t *pUserConfig)
{
tconst XAxiDma_Config_t *pPhyConfig;
tint fd;
tvoid *vAddr;

tpPhyConfig = LookupConfig(devid);
tprintf("DMA phys addr = 0x%x
", (int)pPhyConfig->physDmaAddr);

t//-------------------------------------
t//Get base virtual address for the DMA registers
t//-------------------------------------
tfd = open("/dev/mem", O_RDWR | O_SYNC);
tpUserConfig->fd = fd;

tvAddr = mmap(NULL, pPhyConfig->dmaSize,
tttPROT_READ | PROT_WRITE,
tttMAP_SHARED, fd,
tttpPhyConfig->physDmaAddr);

tif(vAddr == MAP_FAILED) {
ttgoto mmap1_err;
t}

tpUserConfig->virtDmaAddr = (u32)vAddr;
tpUserConfig->dmaSize = pPhyConfig->dmaSize;

t//-------------------------------------
t//Get virtual address for the DMA RX buffer
t//-------------------------------------
tfd = open("/dev/mem", O_RDWR | O_SYNC);
tvAddr = mmap(NULL, pPhyConfig->buffPoolSize,
tttPROT_READ | PROT_WRITE,
tttMAP_SHARED, fd,
tttpPhyConfig->physBuffAddr);

tif(vAddr == MAP_FAILED) {
ttgoto mmap2_err;
t}

tpUserConfig->virtBuffAddr = (u32)vAddr;
tpUserConfig->physBuffAddr = pPhyConfig->physBuffAddr;
tpUserConfig->buffPoolSize = pPhyConfig->buffPoolSize;
tpUserConfig->fpgaPktSize = pPhyConfig->fpgaPktSize;
tpUserConfig->devid = pPhyConfig->DeviceId;

treturn 1;

mmap1_err:
tperror("[dma_driver]ERROR: DMA mmap() failed
");
tclose(fd);
tassert(0);

mmap2_err:
tperror("[dma_driver]ERROR: Buffer mmap failed
");
tmunmap((void*)pUserConfig->virtDmaAddr, pUserConfig->dmaSize);
tclose(fd);
tassert(0);
}