[RESEND PATCH 0/2] STM32 DMA alternative REQ/ACK protocol support

Default REQ/ACK 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.
Due to a possible DMA stream lock when transferring data to/from STM32
USART/UART, add support to select alternative REQ/ACK protocol.

Amelie Delaunay (2):
  dt-bindings: dma: add alternative REQ/ACK protocol selection in
    stm32-dma
  dmaengine: stm32-dma: add alternate REQ/ACK protocol management

 Documentation/devicetree/bindings/dma/st,stm32-dma.yaml | 7 +++++++
 drivers/dma/stm32-dma.c                                 | 8 ++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

-- 
2.25.1

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 <amelie.delaunay@foss.st.com>
---
 drivers/dma/stm32-dma.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/stm32-dma.c b/drivers/dma/stm32-dma.c
index f54ecb123a52..d3aa34b3d2f7 100644
--- a/drivers/dma/stm32-dma.c
+++ b/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,

-- 
2.25.1

Default REQ/ACK 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.
Due to a possible DMA stream lock when transferring data to/from STM32
USART/UART, this new bindings allow to select this alternative protocol in
device tree, especially for STM32 USART/UART nodes.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
---
 Documentation/devicetree/bindings/dma/st,stm32-dma.yaml | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/devicetree/bindings/dma/st,stm32-dma.yaml b/Documentation/devicetree/bindings/dma/st,stm32-dma.yaml
index 2a5325f480f6..4bf676fd25dc 100644
--- a/Documentation/devicetree/bindings/dma/st,stm32-dma.yaml
+++ b/Documentation/devicetree/bindings/dma/st,stm32-dma.yaml

@@ -40,6 +40,13 @@ description: |
          0x0: FIFO mode with threshold selectable with bit 0-1
          0x1: Direct mode: each DMA request immediately initiates a transfer
               from/to the memory, FIFO is bypassed.
+       -bit 4: alternative DMA request/acknowledge protocol
+         0x0: Use standard DMA ACK management, where ACK signal is maintained
+              up to the removal of request and transfer completion
+         0x1: Use alternative DMA ACK management, where ACK de-assertion does
+              not wait for the de-assertion of the REQuest, ACK is only managed
+              by transfer completion. This must only be used on channels
+              managing transfers for STM32 USART/UART.
 
 
 maintainers:

-- 
2.25.1