Kirkwood DMA engine transfer to PCI memory space?

[saeed bishara]

On Wed, Oct 6, 2010 at 11:31 AM, Wolfgang Wegner <ww-ml at gmx.de> wrote:
> Hi all,
>
> I once more started an attempt to implement DMA transfer to the
> PCI memory using the Kirkwood XOR (DMA) engine. The device is
> an FPGA connected to PCIe via a 88SB2211 PCIe->PCI bridge.
>
> That's my PCI device:
> 01:08.0 Class ff00: Device 1731:0101 (rev 10)
>        Control: I/O- Mem+ BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR+ FastB2B- DisINTx-
>        Status: Cap- 66MHz- UDF- FastB2B- ParErr+ DEVSEL=slow >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
>        Region 0: Memory at e0000000 (32-bit, non-prefetchable) [size=64M]
>        Region 1: Memory at e4000000 (32-bit, non-prefetchable) [size=256]
>
> I can write to the 64M buffer space via writel() or map the
> buffer to userspace and then write to it, both successfully.
>
> And this is my DMA transfer function, I guess its source should
> be obvious (dma_async_memcpy_buf_to_buf() slightly castrated):
>
> dma_cookie_t
> dma_async_memcpy_buf_to_dev(struct dma_chan *chan, void *dest,
>                        void *src, size_t len)
> {
>        struct dma_device *dev = chan->device;
>        struct dma_async_tx_descriptor *tx;
>        dma_addr_t dma_dest, dma_src;
>        dma_cookie_t cookie;
>        int cpu;
>        unsigned long flags;
>
>        dma_src = dma_map_single(dev->dev, src, len, DMA_TO_DEVICE);
> #if 0
>        dma_dest = dma_map_single(dev->dev, dest, len, DMA_FROM_DEVICE);
> #else
>        dma_dest = dest;
> #endif
>        flags = DMA_CTRL_ACK |
>                DMA_COMPL_SRC_UNMAP_SINGLE |
>                DMA_COMPL_DEST_UNMAP_SINGLE;
>        tx = dev->device_prep_dma_memcpy(chan, dma_dest, dma_src, len, flags);
>
>        if (!tx) {
>                dma_unmap_single(dev->dev, dma_src, len, DMA_TO_DEVICE);
> //                dma_unmap_single(dev->dev, dma_dest, len, DMA_FROM_DEVICE);
>                return -ENOMEM;
>        }
>
>        tx->callback = NULL;
>        cookie = tx->tx_submit(tx);
>
>        cpu = get_cpu();
>        per_cpu_ptr(chan->local, cpu)->bytes_transferred += len;
>        per_cpu_ptr(chan->local, cpu)->memcpy_count++;
>        put_cpu();
>
>        return cookie;
> }
>
> When using a buffer obtained with dma_alloc_coherent() as the destination
> the transfer works fine. When using the PCI memory address as the
> destination, the transfer silently fails - the buffer simply does not
> change contents, but I did not see any error condition either (cookie
> is always non-negative).
>
> Is there something obvious I am doing wrong? From Kirkwood documentation
> I can not see a limitation of the XOR engine like being able to do
> mem-mem transfers only, neither in the kernel code (which, however, I
> did not yet completely understand).
>
> Any hints would be appreciated!
The XOR DMA engine has "address decoding windows"  that determines
where to route transactions issued by the xor. the kernel configs only
dram windows, you need to open windows for PCI. this ad-hoc code (not
tested) my help:

--- a/drivers/dma/mv_xor.c
+++ b/drivers/dma/mv_xor.c
@@ -1274,6 +1274,15 @@ mv_xor_conf_mbus_windows(struct
mv_xor_shared_private *msp,
                win_enable |= (1 << i);
                win_enable |= 3 << (16 + (2 * i));
        }
+       /* set window 4 for pcie 0 */
+       i = 4;
+        writel((KIRKWOOD_PCIE_MEM_PHYS_BASE & 0xffff0000) |
+              (ATTR_PCIE_MEM << 8) |
+               TARGET_PCIE, base + WINDOW_BASE(i));
+        writel((KIRKWOOD_PCIE_MEM_SIZE - 1) & 0xffff0000, base +
WINDOW_SIZE(i));
+
+       win_enable |= (1 << i);
+        win_enable |= 3 << (16 + (2 * i));



saeed