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From:   Erwan Le Ray <erwan.leray@foss.st.com>
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Alexandre Torgue <alexandre.torgue@foss.st.com>
CC:     <linux-serial@vger.kernel.org>,
        <linux-stm32@st-md-mailman.stormreply.com>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>,
        Erwan Le Ray <erwan.leray@foss.st.com>,
        Fabrice Gasnier <fabrice.gasnier@foss.st.com>,
        Valentin Caron <valentin.caron@foss.st.com>
Subject: [PATCH 13/13] serial: stm32: add support for "flush_buffer" ops
Date:   Fri, 19 Feb 2021 18:47:36 +0100
Message-ID: <20210219174736.1022-14-erwan.leray@foss.st.com>
In-Reply-To: <20210219174736.1022-1-erwan.leray@foss.st.com>
References: <20210219174736.1022-1-erwan.leray@foss.st.com>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

Add the support for "flush_buffer" ops in order to flush any write buffers,
reset any DMA state and stop any ongoing DMA transfers when the
port->state->xmit circular buffer is cleared.

Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 114408f3892a..92836068e5ec 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -597,6 +597,19 @@ static void stm32_usart_start_tx(struct uart_port *port)
 	stm32_usart_transmit_chars(port);
 }
 
+/* Flush the transmit buffer. */
+static void stm32_usart_flush_buffer(struct uart_port *port)
+{
+	struct stm32_port *stm32_port = to_stm32_port(port);
+	struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
+
+	if (stm32_port->tx_ch) {
+		dmaengine_terminate_async(stm32_port->tx_ch);
+		stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
+		stm32_port->tx_dma_busy = false;
+	}
+}
+
 /* Throttle the remote when input buffer is about to overflow. */
 static void stm32_usart_throttle(struct uart_port *port)
 {
@@ -992,6 +1005,7 @@ static const struct uart_ops stm32_uart_ops = {
 	.break_ctl	= stm32_usart_break_ctl,
 	.startup	= stm32_usart_startup,
 	.shutdown	= stm32_usart_shutdown,
+	.flush_buffer	= stm32_usart_flush_buffer,
 	.set_termios	= stm32_usart_set_termios,
 	.pm		= stm32_usart_pm,
 	.type		= stm32_usart_type,
-- 
2.17.1