From a0f0f397c0b410b5736ca24285300c559b982087 Mon Sep 17 00:00:00 2001
From: Valentin Caron <valentin.caron@foss.st.com>
Date: Tue, 8 Aug 2023 18:19:02 +0200
Subject: [PATCH] serial: stm32: use DMAT as a configuration bit

References: bsc#1214683 (PREEMPT_RT prerequisite backports)
Patch-mainline: v6.6-rc1
Git-commit: 00bc5e8fc91743753a3ac9de1e9567e844ae3967

DMAT is a configuration bit so it should be set at the startup of uart
port and not when a DMA transfer begins.

This patch move set of DMAT into set_termios and remove DMAT reset except
in shutdown.

Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Link: https://lore.kernel.org/r/20230808161906.178996-3-valentin.caron@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 drivers/tty/serial/stm32-usart.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 1762b2c62278..a75892980bb8 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -506,10 +506,8 @@ static void stm32_usart_tx_dma_complete(void *arg)
 {
 	struct uart_port *port = arg;
 	struct stm32_port *stm32port = to_stm32_port(port);
-	const struct stm32_usart_offsets *ofs = &stm32port->info->ofs;
 	unsigned long flags;
 
-	stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
 	stm32_usart_tx_dma_terminate(stm32port);
 
 	/* Let's see if we have pending data to send */
@@ -598,7 +596,6 @@ static void stm32_usart_transmit_chars_pio(struct uart_port *port)
 static void stm32_usart_transmit_chars_dma(struct uart_port *port)
 {
 	struct stm32_port *stm32port = to_stm32_port(port);
-	const struct stm32_usart_offsets *ofs = &stm32port->info->ofs;
 	struct circ_buf *xmit = &port->state->xmit;
 	struct dma_async_tx_descriptor *desc = NULL;
 	unsigned int count;
@@ -663,8 +660,6 @@ static void stm32_usart_transmit_chars_dma(struct uart_port *port)
 	/* Issue pending DMA TX requests */
 	dma_async_issue_pending(stm32port->tx_ch);
 
-	stm32_usart_set_bits(port, ofs->cr3, USART_CR3_DMAT);
-
 	uart_xmit_advance(port, count);
 
 	return;
@@ -1266,6 +1261,9 @@ static void stm32_usart_set_termios(struct uart_port *port,
 		cr3 |= USART_CR3_DDRE;
 	}
 
+	if (stm32_port->tx_ch)
+		cr3 |= USART_CR3_DMAT;
+
 	if (rs485conf->flags & SER_RS485_ENABLED) {
 		stm32_usart_config_reg_rs485(&cr1, &cr3,
 					     rs485conf->delay_rts_before_send,