Problems with Freescale DMA driver

[Ira Snyder <iws@ovro.caltech.edu>]

Hello LKML,

I'm developing on a Freescale MPC8349EA MDS evaluation board. I'm
currently testing the DMA controller. It uses the CONFIG_FSL_DMA driver.

All tests were done with a recent git pull.

I built the CONFIG_DMATEST DMA test client, and it runs perfectly in the
absence of other DMA activity. Enabling CONFIG_NET_DMA and running the
DMA test client while network traffic is running causes failures such as
the following:

of-fsl-dma-channel e0008100.dma-channe: DMA halt timeout!
dma0chan0-test0: dstbuf[0x9c0] mismatch! Expected c2, got df
dma0chan0-test0: dstbuf[0x9c1] mismatch! Expected c1, got df
dma0chan0-test0: dstbuf[0x9c2] mismatch! Expected c0, got df
dma0chan0-test0: dstbuf[0x9c3] not copied! Expected df, got 3c
dma0chan0-test0: dstbuf[0x9c4] not copied! Expected de, got 3b
dma0chan0-test0: dstbuf[0x9c5] not copied! Expected dd, got 3a
dma0chan0-test0: dstbuf[0x9c6] not copied! Expected dc, got 39
dma0chan0-test0: dstbuf[0x9c7] not copied! Expected db, got 38
dma0chan0-test0: dstbuf[0x9c8] not copied! Expected da, got 37
dma0chan0-test0: dstbuf[0x9c9] not copied! Expected d9, got 36
dma0chan0-test0: dstbuf[0x9ca] not copied! Expected d8, got 35
dma0chan0-test0: dstbuf[0x9d8] mismatch! Expected ca, got c2
dma0chan0-test0: dstbuf[0x9d9] mismatch! Expected c9, got c1
dma0chan0-test0: dstbuf[0x9da] mismatch! Expected c8, got c0
dma0chan0-test0: dstbuf[0x9db] mismatch! Expected c7, got df
dma0chan0-test0: dstbuf[0x9dc] mismatch! Expected c6, got de
dma0chan0-test0: dstbuf[0x9dd] mismatch! Expected c5, got dd
dma0chan0-test0: dstbuf[0x9de] mismatch! Expected c4, got dc
dma0chan0-test0: dstbuf[0x9df] mismatch! Expected c3, got db
dma0chan0-test0: dstbuf[0x9e0] mismatch! Expected c2, got da
dma0chan0-test0: dstbuf[0x9e1] mismatch! Expected c1, got d9
dma0chan0-test0: dstbuf[0x9e2] mismatch! Expected c0, got d8
dma0chan0-test0: dstbuf[0x9e3] mismatch! Expected df, got d7
dma0chan0-test0: dstbuf[0x9e4] mismatch! Expected de, got d6
dma0chan0-test0: dstbuf[0x9e5] mismatch! Expected dd, got d5
dma0chan0-test0: dstbuf[0x9e6] mismatch! Expected dc, got d4
dma0chan0-test0: dstbuf[0x9e7] mismatch! Expected db, got d3
dma0chan0-test0: dstbuf[0x9e8] mismatch! Expected da, got d2
dma0chan0-test0: dstbuf[0x9e9] mismatch! Expected d9, got d1
dma0chan0-test0: dstbuf[0x9ea] mismatch! Expected d8, got d0
dma0chan0-test0: dstbuf[0x9eb] mismatch! Expected d7, got cf
dma0chan0-test0: dstbuf[0x9ec] mismatch! Expected d6, got ce
dma0chan0-test0: 7011 errors suppressed
dma0chan0-test0: #12268: 7043 errors with src_off=0x1b6b dst_off=0x96e len=0x1be2

Is this to be expected? I thought the whole point of the DMAEngine API
was to enable sharing of DMA channels.

Another issue I noticed was running a network transfer from another
computer to the board. I get the following in dmesg, varying numbers of
times. This is with no other DMA activity running, dmatest is not
loaded. NET_DMA should be the only thing using the controller:

of-fsl-dma-channel e0008100.dma-channe: DMA halt timeout!
of-fsl-dma-channel e0008100.dma-channe: DMA halt timeout!
of-fsl-dma-channel e0008100.dma-channe: DMA halt timeout!
of-fsl-dma-channel e0008100.dma-channe: DMA halt timeout!
of-fsl-dma-channel e0008100.dma-channe: DMA halt timeout!
of-fsl-dma-channel e0008100.dma-channe: DMA halt timeout!
of-fsl-dma-channel e0008100.dma-channe: DMA halt timeout!
of-fsl-dma-channel e0008100.dma-channe: DMA halt timeout!
of-fsl-dma-channel e0008100.dma-channe: DMA halt timeout!

On the run where the above errors were printed,
/sys/class/dma/dma0chan0/memcpy_count increased by ~36000. Certainly the
DMA halt error doesn't happen for every single dma transaction.

Is this normal behavior, or is something broken in the driver?

I've CC'd the maintainers responsible for the FSL DMA driver, as well as
the generic DMA offload system.

Please CC me on any responses, I'm not subscribed to LKML.

I'm happy to help test any changes, or add information if it is needed,
please just ask.

Thanks,
Ira