[PATCH v4 08/14] serial: 8250_mxpcie: speed up TX using memory-mapped FIFO window

[Crescent Hsieh]

The MUEx50 UART provides a memory-mapped TX FIFO data window along with
a TX FIFO level counter.

Fill the TX FIFO in bulk via the MMIO FIFO window based on available
FIFO space, using uart_port_tx_limited() for the common serial-core TX
handling.

Signed-off-by: Crescent Hsieh <crescentcy.hsieh@xxxxxxxx>
---
 drivers/tty/serial/8250/8250_mxpcie.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_mxpcie.c b/drivers/tty/serial/8250/8250_mxpcie.c
index cfef7eee81a8..53f304a17fef 100644
--- a/drivers/tty/serial/8250/8250_mxpcie.c
+++ b/drivers/tty/serial/8250/8250_mxpcie.c
@@ -81,8 +81,10 @@
 #define MOXA_PUART_FCL		0x12	/* Flow Control Low Trigger Level */
 #define MOXA_PUART_FCH		0x13	/* Flow Control High Trigger Level */
 #define MOXA_PUART_RX_FIFO_CNT	0x15	/* Rx FIFO Data Counter */
+#define MOXA_PUART_TX_FIFO_CNT	0x16	/* Tx FIFO Data Counter */
 
 #define MOXA_PUART_RX_FIFO_MEM	0x100	/* Memory Space to Rx FIFO Data Register */
+#define MOXA_PUART_TX_FIFO_MEM	0x100	/* Memory Space to Tx FIFO Data Register */
 
 #define MOXA_GPIO_DIRECTION	0x09
 #define MOXA_GPIO_OUTPUT	0x0A
@@ -306,6 +308,18 @@ static bool mxpcie8250_should_rx(struct uart_8250_port *up, u16 lsr)
 	return false;
 }
 
+static void mxpcie8250_tx_chars(struct uart_8250_port *up)
+{
+	struct uart_port *port = &up->port;
+	unsigned int offset = 0;
+	unsigned char c;
+
+	uart_port_tx_limited(port, c, port->fifosize - serial_in(up, MOXA_PUART_TX_FIFO_CNT),
+			     true,
+			     serial_out(up, MOXA_PUART_TX_FIFO_MEM + offset++, c),
+			     ({}));
+}
+
 static int mxpcie8250_handle_irq(struct uart_port *port)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
@@ -329,7 +343,7 @@ static int mxpcie8250_handle_irq(struct uart_port *port)
 	serial8250_modem_status(up);
 
 	if ((lsr & UART_LSR_THRE) && (up->ier & UART_IER_THRI))
-		serial8250_tx_chars(up);
+		mxpcie8250_tx_chars(up);
 
 	return 1;
 }
-- 
2.45.2