The legacy sdma driver has below limitations or drawbacks:
1. Hardcode the max BDs number as "PAGE_SIZE / sizeof(*)", and alloc
one page size for one channel regardless of only few BDs needed
most time. But in few cases, the max PAGE_SIZE maybe not enough.
2. One SDMA channel can't stop immediatley once channel disabled which
means SDMA interrupt may come in after this channel terminated.There
are some patches for this corner case such as commit "2746e2c389f9",
but not cover non-cyclic.
The common virt-dma overcomes the above limitations. It can alloc bd
dynamically and free bd once this tx transfer done. No memory wasted or
maximum limititation here, only depends on how many memory can be requested
from kernel. For No.2, such issue can be workaround by checking if there
is available descript("sdmac->desc") now once the unwanted interrupt
coming. At last the common virt-dma is easier for sdma driver maintain.
Change from v4:
1. identify lockdep issue which caused by allocate memory with
'GFP_KERNEL', change to 'GFP_NOWAIT' instead so that lockdep
ignore check. That also make sense since Audio/uart driver may
call dma function after spin_lock_irqsave()...
2. use dma pool instead for bd description allocated,since audio
driver may call dma_terminate_all in irq. Please refer to 7/7.
3. remove 7/7 serial patch in v4, since lockdep issued fixed by No.1
Change from v3:
1. add two uart patches which impacted by this patchset.
2. unlock 'vc.lock' before cyclic dma callback and lock again after
it because some driver such as uart will call dmaengine_tx_status
which will acquire 'vc.lock' again and dead lock comes out.
3. remove 'Revert commit' stuff since that patch is not wrong and
combine two patch into one patch as Sascha's comment.
Change from v2:
1. include Sascha's patch to make the main patch easier to review.
Thanks Sacha.
2. remove useless 'desc'/'chan' in struct sdma_channe.
Change from v1:
1. split v1 patch into 5 patches.
2. remove some unnecessary condition check.
3. remove unnecessary 'pending' list.
Robin Gong (6):
tty: serial: imx: correct dma cookie status
dmaengine: imx-sdma: add virt-dma support
dmaengine: imx-sdma: remove useless 'lock' and 'enabled' in 'struct
sdma_channel'
dmaengine: imx-sdma: remove the maximum limitation for bd numbers
dmaengine: imx-sdma: add sdma_transfer_init to decrease code overlap
dmaengine: imx-sdma: alloclate bd memory from dma pool
Sascha Hauer (1):
dmaengine: imx-sdma: factor out a struct sdma_desc from struct
sdma_channel
drivers/dma/Kconfig | 1 +
drivers/dma/imx-sdma.c | 400 +++++++++++++++++++++++++++--------------------
drivers/tty/serial/imx.c | 2 +-
3 files changed, 235 insertions(+), 168 deletions(-)
--
2.7.4
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