Re: FSL DMA engine transfer to PCI memory

[Felix Radensky]

Hi Ira,

On 01/25/2011 06:29 PM, Ira W. Snyder wrote:

On Tue, Jan 25, 2011 at 04:32:02PM +0200, Felix Radensky wrote:

Hi Ira,

On 01/25/2011 02:18 AM, Ira W. Snyder wrote:

On Tue, Jan 25, 2011 at 01:39:39AM +0200, Felix Radensky wrote:

Hi Ira, Scott

On 01/25/2011 12:26 AM, Ira W. Snyder wrote:

On Mon, Jan 24, 2011 at 11:47:22PM +0200, Felix Radensky wrote:

Hi,

I'm trying to use FSL DMA engine to perform DMA transfer from
memory buffer obtained by kmalloc() to PCI memory. This is on
custom board based on P2020 running linux-2.6.35. The PCI
device is Altera FPGA, connected directly to SoC PCI-E controller.

01:00.0 Unassigned class [ff00]: Altera Corporation Unknown device
0004 (rev 01)
            Subsystem: Altera Corporation Unknown device 0004
            Control: I/O- Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop-
ParErr- Stepping- SERR- FastB2B-
            Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast
    >TAbort-<TAbort-<MAbort->SERR-<PERR-
            Interrupt: pin A routed to IRQ 16
            Region 0: Memory at c0000000 (32-bit, non-prefetchable)
[size=128K]
            Capabilities: [50] Message Signalled Interrupts: Mask- 64bit+
Queue=0/0 Enable-
                    Address: 0000000000000000  Data: 0000
            Capabilities: [78] Power Management version 3
                    Flags: PMEClk- DSI- D1- D2- AuxCurrent=0mA
PME(D0-,D1-,D2-,D3hot-,D3cold-)
                    Status: D0 PME-Enable- DSel=0 DScale=0 PME-
            Capabilities: [80] Express Endpoint IRQ 0
                    Device: Supported: MaxPayload 256 bytes, PhantFunc 0,
ExtTag-
                    Device: Latency L0s<64ns, L1<1us
                    Device: AtnBtn- AtnInd- PwrInd-
                    Device: Errors: Correctable- Non-Fatal- Fatal-
Unsupported-
                    Device: RlxdOrd+ ExtTag- PhantFunc- AuxPwr- NoSnoop+
                    Device: MaxPayload 128 bytes, MaxReadReq 512 bytes
                    Link: Supported Speed 2.5Gb/s, Width x1, ASPM L0s, Port 1
                    Link: Latency L0s unlimited, L1 unlimited
                    Link: ASPM Disabled RCB 64 bytes CommClk- ExtSynch-
                    Link: Speed 2.5Gb/s, Width x1
            Capabilities: [100] Virtual Channel


I can successfully writel() to PCI memory via address obtained from
pci_ioremap_bar().
Here's my DMA transfer routine

static int dma_transfer(struct dma_chan *chan, void *dst, void *src,
size_t len)
{
        int rc = 0;
        dma_addr_t dma_src;
        dma_addr_t dma_dst;
        dma_cookie_t cookie;
        struct completion cmp;
        enum dma_status status;
        enum dma_ctrl_flags flags = 0;
        struct dma_device *dev = chan->device;
        struct dma_async_tx_descriptor *tx = NULL;
        unsigned long tmo = msecs_to_jiffies(FPGA_DMA_TIMEOUT_MS);

        dma_src = dma_map_single(dev->dev, src, len, DMA_TO_DEVICE);
        if (dma_mapping_error(dev->dev, dma_src)) {
            printk(KERN_ERR "Failed to map src for DMA\n");
            return -EIO;
        }

        dma_dst = (dma_addr_t)dst;

        flags = DMA_CTRL_ACK |
            DMA_COMPL_SRC_UNMAP_SINGLE  |
            DMA_COMPL_SKIP_DEST_UNMAP |
            DMA_PREP_INTERRUPT;

        tx = dev->device_prep_dma_memcpy(chan, dma_dst, dma_src, len, flags);
        if (!tx) {
            printk(KERN_ERR "%s: Failed to prepare DMA transfer\n",
                   __FUNCTION__);
            dma_unmap_single(dev->dev, dma_src, len, DMA_TO_DEVICE);
            return -ENOMEM;
        }

        init_completion(&cmp);
        tx->callback = dma_callback;
        tx->callback_param =&cmp;
        cookie = tx->tx_submit(tx);

        if (dma_submit_error(cookie)) {
            printk(KERN_ERR "%s: Failed to start DMA transfer\n",
                   __FUNCTION__);
            return -ENOMEM;
        }

        dma_async_issue_pending(chan);

        tmo = wait_for_completion_timeout(&cmp, tmo);
        status = dma_async_is_tx_complete(chan, cookie, NULL, NULL);

        if (tmo == 0) {
            printk(KERN_ERR "%s: Transfer timed out\n", __FUNCTION__);
            rc = -ETIMEDOUT;
        } else if (status != DMA_SUCCESS) {
            printk(KERN_ERR "%s: Transfer failed: status is %s\n",
                   __FUNCTION__,
                   status == DMA_ERROR ? "error" : "in progress");

            dev->device_control(chan, DMA_TERMINATE_ALL, 0);
            rc = -EIO;
        }

        return rc;
}

The destination address is PCI memory address returned by
pci_ioremap_bar().
The transfer silently fails, destination buffer doesn't change
contents, but no
error condition is reported.

What am I doing wrong ?

Thanks a lot in advance.

Your destination address is wrong. The device_prep_dma_memcpy() routine
works in physical addresses only (dma_addr_t type). Your source address
looks fine: you're using the result of dma_map_single(), which returns a
physical address.

Your destination address should be something that comes from struct
pci_dev.resource[x].start + offset if necessary. In your lspci output
above, that will be 0xc0000000.

Another possible problem: AFAIK you must use the _ONSTACK() variants
from include/linux/completion.h for struct completion which are on the
stack.

Hope it helps,
Ira

Thanks for your help. I'm now passing the result of
pci_resource_start(pdev, 0)
as destination address, and destination buffer changes after the
transfer. But
the contents of source and destination buffers are different. What
else could
be wrong ?

After you changed the dst address to pci_resource_start(pdev, 0), I
don't see anything wrong with the code.

Try using memcpy_toio() to copy some bytes to the FPGA. Also try writing
a single byte at a time (writeb()?) in a loop. This should help
establish that your device is working.

If you put some pattern in your src buffer (such as 0x0, 0x1, 0x2, ...
0xff, repeat) does the destination show some pattern after the DMA
completes? (Such as, every 4th byte is correct.)

Ira

memcpy_toio() works fine, the data is written correctly. After
DMA, the correct data appears at offsets 0xC, 0x1C, 0x2C, etc.
of the destination buffer. I have 12 bytes of junk, 4 bytes of
correct data, then again 12 bytes of junk and so on.

This sounds like your FPGA doesn't handle burst mode accesses correctly.
A logic analyzer will help you prove it.

Another quick test to try is using an unaligned transfer and see what
happens. The 83xx DMA controller handles unaligned transfers by doing
several small, non-burst transfers until the src and dst are aligned,
and then does cacheline size burst transfers until complete. I hunch the
85xx/86xx controller behaves the same way.

Something like this:

dma_src = dma_map_single(...);
dma_dst = pci_resource_start(pdev, 0) + 1;

Notice that the dst address is offset by one byte, so you'll need to
take that into account when comparing data after the transfer.

Ira

Thanks a lot for your help. It seems the problem was in fsldma.c code,
which was fixed in later kernels (I'm using 2.6.35). The BWC field
in MR register was not set, resulting in single-byte transfers. This
did not work well with FPGA which implements a FIFO with minimal
transfer unit of 32 bits. After setting BWC field DMA works fine.

Felix.
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