[stable 4.19+][PATCH 20/20] dmaengine: stm32-dma: check whether length is aligned on FIFO threshold

[Mathieu Poirier]

From: Pierre-Yves MORDRET <pierre-yves.mordret@xxxxxx>

commit cc832dc8e32785a730ba07c3a357e17c201a5df8 upstream

When a period length is not multiple of FIFO some data may be stuck
within FIFO.

Burst/FIFO Threshold/Period or buffer length check has to be hardened

In any case DMA will grant any request from client but will degraded
any parameters whether awkward.

Signed-off-by: Pierre-Yves MORDRET <pierre-yves.mordret@xxxxxx>
Signed-off-by: Vinod Koul <vkoul@xxxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx> # 4.19+
Signed-off-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
---
 drivers/dma/stm32-dma.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
index 379e8d534e61..4903a408fc14 100644
--- a/drivers/dma/stm32-dma.c
+++ b/drivers/dma/stm32-dma.c
@@ -308,20 +308,12 @@ static bool stm32_dma_fifo_threshold_is_allowed(u32 burst, u32 threshold,
 
 static bool stm32_dma_is_burst_possible(u32 buf_len, u32 threshold)
 {
-	switch (threshold) {
-	case STM32_DMA_FIFO_THRESHOLD_FULL:
-		if (buf_len >= STM32_DMA_MAX_BURST)
-			return true;
-		else
-			return false;
-	case STM32_DMA_FIFO_THRESHOLD_HALFFULL:
-		if (buf_len >= STM32_DMA_MAX_BURST / 2)
-			return true;
-		else
-			return false;
-	default:
-		return false;
-	}
+	/*
+	 * Buffer or period length has to be aligned on FIFO depth.
+	 * Otherwise bytes may be stuck within FIFO at buffer or period
+	 * length.
+	 */
+	return ((buf_len % ((threshold + 1) * 4)) == 0);
 }
 
 static u32 stm32_dma_get_best_burst(u32 buf_len, u32 max_burst, u32 threshold,
-- 
2.17.1