dmaengine: ste_dma40: Recover coalesced cyclic callbacks

DMA40 has one terminal-count status bit per channel, so cyclic period
interrupts can coalesce.

Use the memory-side pointer displacement to queue the minimum observable
number of callbacks. If sampling fails, queue one callback and invalidate
the saved position; the next successful sample resynchronizes without
recounting it.

The pointer is modulo the cyclic buffer: a displacement of d periods can
mean d plus n complete iterations of the buffer. Report d, so the driver
could have missed n iterations of the buffer; DMA40 has no counter to
recover them. For an unchanged pointer, report one callback rather than
risk a spurious full-buffer burst.

This condition has not been seen in practice and is only a product of
review comments that the buffer can miss interrupts.

The preceding cyclic-residue fix ensures that every cyclic period fits in
one LLI, so each boundary corresponds to one client callback.

Fixes: 0c842b551063 ("dma40: cyclic xfer support")
Assisted-by: LLM
Signed-off-by: Linus Walleij <linusw@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260927-dma40-fixes-v7-3-89f595e8851d@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>

0 files changed, 0 insertions, 0 deletions