XAPP1129 DMA Problem

[coldwarcomms]

Hello,

I am trying to get the XAPP1129 pcore running on my ML510 system. I am having trouble booting the kernel. It is failing in this function in include/asm-generic/dma-mappings-common.h:

static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr,
                          size_t size,
                          enum dma_data_direction dir,
                          struct dma_attrs *attrs)
{
    struct dma_map_ops *ops = get_dma_ops(dev);
    dma_addr_t addr;

    kmemcheck_mark_initialized(ptr, size);
    BUG_ON(!ops);
    BUG_ON(!valid_dma_direction(dir));
    addr = ops->map_page(dev, virt_to_page(ptr),
                 (unsigned long)ptr & ~PAGE_MASK, size,
                 dir, attrs);
    debug_dma_map_page(dev, virt_to_page(ptr),
               (unsigned long)ptr & ~PAGE_MASK, size,
               dir, addr, true);
    return addr;
}

It is failing the BUG_ON(!ops) line. The call to dma_map_single_attrs is being made from xll_example.c as follows:

new_buff_physaddr = (u32) dma_map_single(NULL, rx_buff->data,
                                                 LL_EX_BUF_SIZE,
                                                 DMA_FROM_DEVICE);

In case you are confused about the funtion names, this is in dma-mapping-common.h:

#define dma_map_single(d, a, s, r) dma_map_single_attrs(d, a, s, r, NULL)

Anyways, it looks like passing in NULL as the first parameter could be causing the problem. Is there some other way this should be done?

By the way, I am running the newest kernel version from the xilinx tree.

Thank you,

-Nick

[linnj]

I think you're seeing where the kernel has changed since that app note was written so that you have to pass a valid device to the API.

I had to make changes to our emac driver for that at one time also, not too long ago.

You should have a valid device to pass somewhere in your driver.

Thanks.

[coldwarcomms · Accepted solution]

Thanks John,

I took a look at the LLTEMAC driver. I modified all dma_map_single/dma_unmap_single calls to take a device pointer instead of NULL as the first parameter. I got the device structure in xll_example_of_probe using &ofdev->dev and stored it in a global variable for later use by the various functions. Everything seems to work correctly now.

-Nick

[borja_mrtnz]

Hi,

I'm writing a Linux driver (based on XAPP1129) for a custom peripheral which uses DMA to transfer data to DDR2. I'm facing the same problem: our kernel halts at the same point.

Could you post your code to try to solve the problem?

Thank you in advance.

[coldwarcomms]

Hey,

Sure thing. Just go here: http://fpga.ce.rit.edu/?p=linux-2.6-xlnx.git;a=summary and take a look at the latest commit (611ce1ab6280122a42c2882f2909bf05786b99a7).

-Nick

[borja_mrtnz]

Thank you very much!

Finally the kernel booted with the steps you gave. Now is the time to probe if the driver works as we want.

One kudo for you!