serial: stm32: move tx dma terminate DMA to shutdown

Terminate DMA transaction and clear CR3_DMAT when shutdown is requested,
instead of when remove is requested. If DMA transfer is not stopped in
shutdown ops, driver will fail to start a new DMA transfer after next
startup ops.

Fixes: 3489187 ("serial: stm32: adding dma support")
Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Link: https://lore.kernel.org/r/20220104182445.4195-2-valentin.caron@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: VCASTM

drivers/tty/serial/stm32-usart.c

@@ -883,6 +883,11 @@ static void stm32_usart_shutdown(struct uart_port *port)
 	u32 val, isr;
 	int ret;
 
+	if (stm32_port->tx_dma_busy) {
+		dmaengine_terminate_async(stm32_port->tx_ch);
+		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
+	}
+
 	/* Disable modem control interrupts */
 	stm32_usart_disable_ms(port);
 
@@ -1570,7 +1575,6 @@ static int stm32_usart_serial_remove(struct platform_device *pdev)
 	writel_relaxed(cr3, port->membase + ofs->cr3);
 
 	if (stm32_port->tx_ch) {
-		dmaengine_terminate_async(stm32_port->tx_ch);
 		stm32_usart_of_dma_tx_remove(stm32_port, pdev);
 		dma_release_channel(stm32_port->tx_ch);
 	}