[PATCH 2/2] dmaengine: stm32-dma: fix residue in case of MDMA chaining

[Amelie Delaunay]

In case of MDMA chaining, DMA is configured in Double-Buffer Mode (DBM)
with two periods, but if transfer has been prepared with _prep_slave_sg(),
the transfer is not marked cyclic (=!chan->desc->cyclic). However, as DBM
is activated for MDMA chaining, residue computation must take into account
cyclic constraints.

With only two periods in MDMA chaining, and no update due to Transfer
Complete interrupt masked, n_sg is always 0. If DMA current memory address
(depending on SxCR.CT and SxM0AR/SxM1AR) does not correspond, it means n_sg
should be increased.
Then, the residue of the current period is the one read from SxNDTR and
should not be overwritten with the full period length.

Fixes: 723795173ce1 ("dmaengine: stm32-dma: add support to trigger STM32 MDMA")
Signed-off-by: Amelie Delaunay <amelie.delaunay at foss.st.com>
Cc: stable at vger.kernel.org
---
 drivers/dma/stm32-dma.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
index 7427acc82259..0b30151fb45c 100644
--- a/drivers/dma/stm32-dma.c
+++ b/drivers/dma/stm32-dma.c
@@ -1389,11 +1389,12 @@ static size_t stm32_dma_desc_residue(struct stm32_dma_chan *chan,
 
 	residue = stm32_dma_get_remaining_bytes(chan);
 
-	if (chan->desc->cyclic && !stm32_dma_is_current_sg(chan)) {
+	if ((chan->desc->cyclic || chan->trig_mdma) && !stm32_dma_is_current_sg(chan)) {
 		n_sg++;
 		if (n_sg == chan->desc->num_sgs)
 			n_sg = 0;
-		residue = sg_req->len;
+		if (!chan->trig_mdma)
+			residue = sg_req->len;
 	}
 
 	/*
@@ -1403,7 +1404,7 @@ static size_t stm32_dma_desc_residue(struct stm32_dma_chan *chan,
 	 * residue = remaining bytes from NDTR + remaining
 	 * periods/sg to be transferred
 	 */
-	if (!chan->desc->cyclic || n_sg != 0)
+	if ((!chan->desc->cyclic && !chan->trig_mdma) || n_sg != 0)
 		for (i = n_sg; i < desc->num_sgs; i++)
 			residue += desc->sg_req[i].len;
 
-- 
2.25.1