AXI_DMA device driver for Linux

Does any one know how to use the AXI_DMA device driver linux-xlnx/drivers/dma/xilinx_dma.c?
Does it work, has anyone tested it for AXI_DMA IP?
I need to use it as a module.

I have a bare metal AXI_DMA driver but porting it to Linux seems more complicated than I though.

I am new to Linux device drivers, this might be a trivial question for some of you.

Thanks,
Silviu

0 Former Member over 12 years ago

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. :-)
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0 Former Member over 12 years ago

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

Thank you,
Silviu
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0 Former Member over 12 years ago in reply to Former Member

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()?
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0 Former Member over 12 years ago in reply to Former Member

Hi Silviu,
hete is my solution http://www.arbot.cz/post/2013/03/20/VDMA-on-ZedBoard.aspx.
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0 Former Member over 12 years ago in reply to Former Member

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.
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0 Former Member over 12 years ago in reply to Former Member

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
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0 Former Member over 12 years ago in reply to Former Member

Thanks, it helps a lot.

Silviu
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0 Former Member over 12 years ago

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

Thanks,
Silviu
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0 Former Member over 12 years ago

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

Functional solution is interesting for me.

Vatu
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0 Former Member over 11 years ago in reply to Former Member

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);
}
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