Re: FSL DMA engine transfer to PCI memory

Felix Radensky Mon, 24 Jan 2011 15:39:29 -0800

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 ofpci_resource_start(pdev, 0)as destination address, and destination buffer changes after thetransfer. Butthe contents of source and destination buffers are different. Whatelse could

be wrong ?

Thanks.

Felix.

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Re: FSL DMA engine transfer to PCI memory

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