dmaengine: stm32-mdma: use Link Address Register to compute residue

Current implementation relies on curr_hwdesc index. But to keep this index
up to date, Block Transfer interrupt (BTIE) has to be enabled.
If it is not, curr_hwdesc is not updated, and then residue is not reliable.
Rely on Link Address Register instead. And disable BTIE interrupt
in stm32_mdma_setup_xfer() because it is no more needed in case of
_prep_slave_sg() to maintain curr_hwdesc up to date.

Change-Id: I515f6d10d14ef4d3f5432b197e0ea0eb76fc7da7
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/linux-stm32/+/320986
Tested-by: Alain VOLMAT <alain.volmat@foss.st.com>
ACI: CITOOLS <MDG-smet-aci-reviews@list.st.com>
ACI: CIBUILD <MDG-smet-aci-builds@list.st.com>
Reviewed-by: Alain VOLMAT <alain.volmat@foss.st.com>

Author: ADESTM

drivers/dma/stm32-mdma.c

@@ -778,8 +778,6 @@ static int stm32_mdma_setup_xfer(struct stm32_mdma_chan *chan,
 	/* Enable interrupts */
 	ccr &= ~STM32_MDMA_CCR_IRQ_MASK;
 	ccr |= STM32_MDMA_CCR_TEIE | STM32_MDMA_CCR_CTCIE;
-	if (sg_len > 1)
-		ccr |= STM32_MDMA_CCR_BTIE;
 	desc->ccr = ccr;
 
 	return 0;
@@ -1326,20 +1324,21 @@ static size_t stm32_mdma_desc_residue(struct stm32_mdma_chan *chan,
 {
 	struct stm32_mdma_device *dmadev = stm32_mdma_get_dev(chan);
 	struct stm32_mdma_hwdesc *hwdesc;
-	u32 cisr, cbndtr, residue, modulo, burst_size;
+	u32 cisr, clar, cbndtr, residue, modulo, burst_size;
 	int i;
 
 	cisr = stm32_mdma_read(dmadev, STM32_MDMA_CISR(chan->id));
-	/* Check if Block Transfer Complete is pending, curr_hwdesc not yet updated */
-	if (cisr & STM32_MDMA_CISR_BTIF) {
-		curr_hwdesc++;
-		if(desc->cyclic && curr_hwdesc == desc->count)
-			curr_hwdesc = 0;
-	}
 
 	residue = 0;
-	for (i = curr_hwdesc + 1; i < desc->count; i++) {
+	/* Get the next hw descriptor to process from current transfer */
+	clar = stm32_mdma_read(dmadev, STM32_MDMA_CLAR(chan->id));
+	for (i = desc->count - 1; i >= 0; i--) {
 		hwdesc = desc->node[i].hwdesc;
+
+		if (hwdesc->clar == clar)
+			break;/* Current transfer found, stop cumulating */
+
+		/* Cumulate residue of unprocessed hw descriptors */
 		residue += STM32_MDMA_CBNDTR_BNDT(hwdesc->cbndtr);
 	}
 	cbndtr = stm32_mdma_read(dmadev, STM32_MDMA_CBNDTR(chan->id));