serial: stm32: move RX dma initialization to startup

The RX dma channel is kept active forever (from the probe). That prevents
going to low power mode when it is used. So move the configuration and
enabling/disabling procedures to the startup/shutdown routines.

Signed-off-by: Erwan Le Ray <erwan.leray@st.com>
Change-Id: Ia06918fbdd07d04e4f5bb8d54a2a5841e0bf6f3d
Reviewed-on: https://gerrit.st.com/c/mpu/oe/st/linux-stm32/+/155437
Reviewed-by: CITOOLS <smet-aci-reviews@lists.codex.cro.st.com>
Reviewed-by: CIBUILD <smet-aci-builds@lists.codex.cro.st.com>
Reviewed-by: Fabrice GASNIER <fabrice.gasnier@st.com>

Author: Erwan Le Ray

drivers/tty/serial/stm32-usart.c

@@ -692,6 +692,8 @@ static int stm32_startup(struct uart_port *port)
 	struct stm32_port *stm32_port = to_stm32_port(port);
 	struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
 	const char *name = to_platform_device(port->dev)->name;
+	struct dma_async_tx_descriptor *desc = NULL;
+	dma_cookie_t cookie;
 	u32 val;
 	int ret;
 
@@ -705,6 +707,29 @@ static int stm32_startup(struct uart_port *port)
 	if (ofs->rqr != UNDEF_REG)
 		stm32_set_bits(port, ofs->rqr, USART_RQR_RXFRQ);
 
+	if (stm32_port->rx_ch) {
+		stm32_port->last_res = RX_BUF_L;
+		/* Prepare a DMA cyclic transaction */
+		desc = dmaengine_prep_dma_cyclic(stm32_port->rx_ch,
+						 stm32_port->rx_dma_buf,
+						 RX_BUF_L, RX_BUF_P,
+						 DMA_DEV_TO_MEM,
+						 DMA_PREP_INTERRUPT);
+		if (!desc) {
+			dev_err(port->dev, "rx dma prep cyclic failed\n");
+			return -ENODEV;
+		}
+
+		desc->callback = stm32_rx_dma_complete;
+		desc->callback_param = port;
+
+		/* Push current DMA transaction in the pending queue */
+		cookie = dmaengine_submit(desc);
+
+		/* Issue pending DMA requests */
+		dma_async_issue_pending(stm32_port->rx_ch);
+	}
+
 	/* RX enabling */
 	val = stm32_port->cr1_irq | USART_CR1_RE;
 	stm32_set_bits(port, ofs->cr1, val);
@@ -740,6 +765,9 @@ static void stm32_shutdown(struct uart_port *port)
 		stm32_clr_bits(port, ofs->cr3,
 			       USART_CR3_TXFTIE | USART_CR3_RXFTIE);
 
+	if (stm32_port->rx_ch)
+		dmaengine_terminate_async(stm32_port->rx_ch);
+
 	free_irq(port->irq, port);
 }
 
@@ -1165,8 +1193,6 @@ static int stm32_of_dma_rx_probe(struct stm32_port *stm32port,
 	struct uart_port *port = &stm32port->port;
 	struct device *dev = &pdev->dev;
 	struct dma_slave_config config;
-	struct dma_async_tx_descriptor *desc = NULL;
-	dma_cookie_t cookie;
 	int ret;
 
 	/* Request DMA RX channel */
@@ -1195,26 +1221,6 @@ static int stm32_of_dma_rx_probe(struct stm32_port *stm32port,
 		goto config_err;
 	}
 
-	/* Prepare a DMA cyclic transaction */
-	desc = dmaengine_prep_dma_cyclic(stm32port->rx_ch,
-					 stm32port->rx_dma_buf,
-					 RX_BUF_L, RX_BUF_P, DMA_DEV_TO_MEM,
-					 DMA_PREP_INTERRUPT);
-	if (!desc) {
-		dev_err(dev, "rx dma prep cyclic failed\n");
-		ret = -ENODEV;
-		goto config_err;
-	}
-
-	desc->callback = stm32_rx_dma_complete;
-	desc->callback_param = port;
-
-	/* Push current DMA transaction in the pending queue */
-	cookie = dmaengine_submit(desc);
-
-	/* Issue pending DMA requests */
-	dma_async_issue_pending(stm32port->rx_ch);
-
 	return 0;
 
 config_err:
@@ -1335,10 +1341,8 @@ static int stm32_serial_probe(struct platform_device *pdev)
 	return 0;
 
 err_dma:
-	if (stm32port->rx_ch) {
-		dmaengine_terminate_async(stm32port->rx_ch);
+	if (stm32port->rx_ch)
 		dma_release_channel(stm32port->rx_ch);
-	}
 
 	if (stm32port->rx_dma_buf)
 		dma_free_coherent(&pdev->dev,
@@ -1387,10 +1391,8 @@ static int stm32_serial_remove(struct platform_device *pdev)
 	cr3 &= ~USART_CR3_DDRE;
 	writel_relaxed(cr3, port->membase + ofs->cr3);
 
-	if (stm32_port->rx_ch) {
-		dmaengine_terminate_async(stm32_port->rx_ch);
+	if (stm32_port->rx_ch)
 		dma_release_channel(stm32_port->rx_ch);
-	}
 
 	if (stm32_port->rx_dma_buf)
 		dma_free_coherent(&pdev->dev,