dmaengine: shdma: fix a race condition in __ld_cleanup()

dmaengine: shdma: fix a race condition in __ld_cleanup()

This patch fixes a race condition about a list of shdma-base driver.
If we don't apply this patch, a dma slave driver (especially a usb
peripheral driver) may not be able to start the transfer.

If a dma slave driver has a callback, __ld_cleanup() will call
the callback before this driver removes the list. After the callback,
since the return value of __ld_cleanup() is not zero,
shdma_chan_ld_cleanup() calls __ld_cleanup() again. And, __ld_clean()
will removes the list.

At this time, if a dma slave driver calls dmaengine_submit() before
this driver removes the list, this driver will set schan->pm_state
to SHDMA_PM_PENDING in shdma_tx_submit(). And then, even if a dma
slave driver calls dma_async_issue_pending(), this driver don't
start the transfer because the schan->pm_state is SHDMA_PM_PENDING
in shdma_issue_pending().

So, this patch adds a new condition in __ld_clean() to check if the
schan->pm_state is SHDMA_PM_PENDING or not.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>