[v1,1/1] dmaengine: stm32-dma: check whether length is aligned on FIFO threshold

Commit Message

Pierre Yves MORDRET Sept. 11, 2018, 7:31 a.m. UTC

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 <[e-mail]>
---
  Version history:
    v1:
       * Initial
---
---
 drivers/dma/stm32-dma.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

Comments

Vinod Koul Oct. 2, 2018, 3:02 p.m. UTC | #1

On 11-09-18, 09:31, Pierre-Yves MORDRET wrote:
> 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.

Applied, thanks

Patch

diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
index 379e8d5..4903a40 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,