[PATCH 1/4] dmaengine: stm32-dma: rework irq handler to manage error before xfer events

[Amelie Delaunay]

To better understand error that can be detected by the DMA controller,
manage the error flags before the transfer flags.
This way, it is possible to know if the FIFO error flag is set for an
over/underrun condition or a FIFO level error.
When a FIFO over/underrun condition occurs, the data is not lost because
peripheral request is not acknowledged by the stream until the over/
underrun condition is cleared. If this acknowledge takes too much time,
the peripheral itself may detect an over/underrun condition of its internal
buffer and data might be lost.
That's why in case the FIFO error flag is set, we check if the channel is
disabled or not, and if a Transfer Complete flag is set, which means that
the channel is disabled because of the end of transfer.
Because channel is disabled by hardware either by a FIFO level error, or by
an end of transfer.

Signed-off-by: Amelie Delaunay <amelie.delaunay at st.com>
---
 drivers/dma/stm32-dma.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
index d0055d2f0b9a..55a6bd381219 100644
--- a/drivers/dma/stm32-dma.c
+++ b/drivers/dma/stm32-dma.c
@@ -648,21 +648,12 @@ static irqreturn_t stm32_dma_chan_irq(int irq, void *devid)
 	scr = stm32_dma_read(dmadev, STM32_DMA_SCR(chan->id));
 	sfcr = stm32_dma_read(dmadev, STM32_DMA_SFCR(chan->id));
 
-	if (status & STM32_DMA_TCI) {
-		stm32_dma_irq_clear(chan, STM32_DMA_TCI);
-		if (scr & STM32_DMA_SCR_TCIE)
-			stm32_dma_handle_chan_done(chan);
-		status &= ~STM32_DMA_TCI;
-	}
-	if (status & STM32_DMA_HTI) {
-		stm32_dma_irq_clear(chan, STM32_DMA_HTI);
-		status &= ~STM32_DMA_HTI;
-	}
 	if (status & STM32_DMA_FEI) {
 		stm32_dma_irq_clear(chan, STM32_DMA_FEI);
 		status &= ~STM32_DMA_FEI;
 		if (sfcr & STM32_DMA_SFCR_FEIE) {
-			if (!(scr & STM32_DMA_SCR_EN))
+			if (!(scr & STM32_DMA_SCR_EN) &&
+			    !(status & STM32_DMA_TCI))
 				dev_err(chan2dev(chan), "FIFO Error\n");
 			else
 				dev_dbg(chan2dev(chan), "FIFO over/underrun\n");
@@ -674,6 +665,19 @@ static irqreturn_t stm32_dma_chan_irq(int irq, void *devid)
 		if (sfcr & STM32_DMA_SCR_DMEIE)
 			dev_dbg(chan2dev(chan), "Direct mode overrun\n");
 	}
+
+	if (status & STM32_DMA_TCI) {
+		stm32_dma_irq_clear(chan, STM32_DMA_TCI);
+		if (scr & STM32_DMA_SCR_TCIE)
+			stm32_dma_handle_chan_done(chan);
+		status &= ~STM32_DMA_TCI;
+	}
+
+	if (status & STM32_DMA_HTI) {
+		stm32_dma_irq_clear(chan, STM32_DMA_HTI);
+		status &= ~STM32_DMA_HTI;
+	}
+
 	if (status) {
 		stm32_dma_irq_clear(chan, status);
 		dev_err(chan2dev(chan), "DMA error: status=0x%08x\n", status);
-- 
2.17.1