dmaengine: ste_dma40: Fix cyclic transfer residue

DMA40 reads residue from the element count of the currently active LLI.
For a cyclic transfer this reports at most one period, not the bytes
remaining until the cyclic buffer wraps.

Once DMA40 advertises burst granularity, DMAengine PCM uses this residue
directly. For a four-period PCM buffer it consequently reports the
hardware pointer near three periods after every period interrupt. ALSA
eventually stops playback with -EIO although DMA period callbacks
continue.

Calculate cyclic residue from the current memory-side hardware pointer
instead. Read the destination pointer for capture and the source pointer
for playback. Sample the split logical channel pointer coherently and
retain the last valid residue during relink transitions.

Make at most three residue sampling attempts: one initial read plus two
retries. The retries let transient split-register updates or LLI relink
windows settle, while the limit prevents unbounded polling if hardware does
not yield a valid pointer.

This avoids counting terminal-count interrupts, which races with hardware
advancing to the next LLI and cannot account for coalesced interrupt
status. Also reject cyclic periods that expand into multiple LLIs because
logical cyclic LLIs each request a terminal-count interrupt and would
generate more than one callback per period.

Reject invalid cyclic geometries before dividing or constructing the
scatterlist as well.

Reported-by: Frank Li <Frank.li@oss.nxp.com>
Closes: https://lore.kernel.org/dmaengine/aq2wIPJW6viUxyy9@SMW015318/
Fixes: 15c606686541 ("dmaengine: ste_dma40: indicate granularity on channels")
Assisted-by: LLM
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>
Link: https://patch.msgid.link/20260927-dma40-fixes-v7-2-89f595e8851d@kernel.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>

0 files changed, 0 insertions, 0 deletions