dmaengine: stm32-dma: add alternate REQ/ACK protocol management

STM32 USART/UART is not managing correctly the default DMA REQ/ACK protocol
leading to possibly lock the DMA stream.
Default protocol consists in maintaining ACK signal up to the removal of
REQuest and the transfer completion.
In case of alternative REQ/ACK protocol, ACK de-assertion does not wait the
removal of the REQuest, but only the transfer completion.

This patch retrieves the need of the alternative protocol through the
device tree, and sets the protocol accordingly.
It also unwrap STM32_DMA_DIRECT_MODE_GET macro definition for consistency
with new STM32_DMA_ALT_ACK_MODE_GET macro definition.

Signed-off-by: Amelie Delaunay <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Vinod Koul <[email protected]>

drivers/dma/stm32-dma.c

@@ -60,6 +60,7 @@
 #define STM32_DMA_SCR_PSIZE_GET(n)	((n & STM32_DMA_SCR_PSIZE_MASK) >> 11)
 #define STM32_DMA_SCR_DIR_MASK		GENMASK(7, 6)
 #define STM32_DMA_SCR_DIR(n)		((n & 0x3) << 6)
+#define STM32_DMA_SCR_TRBUFF		BIT(20) /* Bufferable transfer for USART/UART */
 #define STM32_DMA_SCR_CT		BIT(19) /* Target in double buffer */
 #define STM32_DMA_SCR_DBM		BIT(18) /* Double Buffer Mode */
 #define STM32_DMA_SCR_PINCOS		BIT(15) /* Peripheral inc offset size */
@@ -138,8 +139,9 @@
 #define STM32_DMA_THRESHOLD_FTR_MASK	GENMASK(1, 0)
 #define STM32_DMA_THRESHOLD_FTR_GET(n)	((n) & STM32_DMA_THRESHOLD_FTR_MASK)
 #define STM32_DMA_DIRECT_MODE_MASK	BIT(2)
-#define STM32_DMA_DIRECT_MODE_GET(n)	(((n) & STM32_DMA_DIRECT_MODE_MASK) \
-					 >> 2)
+#define STM32_DMA_DIRECT_MODE_GET(n)	(((n) & STM32_DMA_DIRECT_MODE_MASK) >> 2)
+#define STM32_DMA_ALT_ACK_MODE_MASK	BIT(4)
+#define STM32_DMA_ALT_ACK_MODE_GET(n)	(((n) & STM32_DMA_ALT_ACK_MODE_MASK) >> 4)
 
 enum stm32_dma_width {
 	STM32_DMA_BYTE,
@@ -1252,6 +1254,8 @@ static void stm32_dma_set_config(struct stm32_dma_chan *chan,
 	chan->threshold = STM32_DMA_THRESHOLD_FTR_GET(cfg->features);
 	if (STM32_DMA_DIRECT_MODE_GET(cfg->features))
 		chan->threshold = STM32_DMA_FIFO_THRESHOLD_NONE;
+	if (STM32_DMA_ALT_ACK_MODE_GET(cfg->features))
+		chan->chan_reg.dma_scr |= STM32_DMA_SCR_TRBUFF;
 }
 
 static struct dma_chan *stm32_dma_of_xlate(struct of_phandle_args *dma_spec,