linux-kernel - [PATCH 1/1] tty: serial: owl: Add support for kernel debugger

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Date:   Fri, 29 May 2020 18:50:25 +0300
From:   Cristian Ciocaltea <cristian.ciocaltea@...il.com>
To:     Andreas Färber <afaerber@...e.de>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>
Cc:     linux-serial@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-actions@...ts.infradead.org
Subject: [PATCH 1/1] tty: serial: owl: Add support for kernel debugger

Implement poll_put_char and poll_get_char callbacks in struct uart_ops
that enables OWL UART to be used for KGDB debugging over serial line.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...il.com>
---
 drivers/tty/serial/owl-uart.c | 45 ++++++++++++++++++++++++++++++-----
 1 file changed, 39 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/owl-uart.c b/drivers/tty/serial/owl-uart.c
index c2fa2f15d50a..26dcc374dec5 100644
--- a/drivers/tty/serial/owl-uart.c
+++ b/drivers/tty/serial/owl-uart.c
@@ -12,6 +12,7 @@
 #include <linux/console.h>
 #include <linux/delay.h>
 #include <linux/io.h>
+#include <linux/iopoll.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
@@ -20,13 +21,13 @@
 #include <linux/tty.h>
 #include <linux/tty_flip.h>
 
-#define OWL_UART_PORT_NUM 7
-#define OWL_UART_DEV_NAME "ttyOWL"
+#define OWL_UART_PORT_NUM		7
+#define OWL_UART_DEV_NAME		"ttyOWL"
 
-#define OWL_UART_CTL	0x000
-#define OWL_UART_RXDAT	0x004
-#define OWL_UART_TXDAT	0x008
-#define OWL_UART_STAT	0x00c
+#define OWL_UART_CTL			0x000
+#define OWL_UART_RXDAT			0x004
+#define OWL_UART_TXDAT			0x008
+#define OWL_UART_STAT			0x00c
 
 #define OWL_UART_CTL_DWLS_MASK		GENMASK(1, 0)
 #define OWL_UART_CTL_DWLS_5BITS		(0x0 << 0)
@@ -461,6 +462,34 @@ static void owl_uart_config_port(struct uart_port *port, int flags)
 	}
 }
 
+#ifdef CONFIG_CONSOLE_POLL
+
+static int owl_uart_poll_get_char(struct uart_port *port)
+{
+	u32 c = NO_POLL_CHAR;
+
+	if (!(owl_uart_read(port, OWL_UART_STAT) & OWL_UART_STAT_RFEM))
+		c = owl_uart_read(port, OWL_UART_RXDAT);
+
+	return c;
+}
+
+static void owl_uart_poll_put_char(struct uart_port *port, unsigned char c)
+{
+	/* Wait while TX FIFO is full */
+	while (owl_uart_read(port, OWL_UART_STAT) & OWL_UART_STAT_TFFU)
+		cpu_relax();
+
+	/* Send the character out */
+	owl_uart_write(port, c, OWL_UART_TXDAT);
+
+	/* Wait for transmitter to become empty */
+	while (owl_uart_read(port, OWL_UART_STAT) & OWL_UART_STAT_TRFL_MASK)
+		cpu_relax();
+}
+
+#endif /* CONFIG_CONSOLE_POLL */
+
 static const struct uart_ops owl_uart_ops = {
 	.set_mctrl = owl_uart_set_mctrl,
 	.get_mctrl = owl_uart_get_mctrl,
@@ -476,6 +505,10 @@ static const struct uart_ops owl_uart_ops = {
 	.request_port = owl_uart_request_port,
 	.release_port = owl_uart_release_port,
 	.verify_port = owl_uart_verify_port,
+#ifdef CONFIG_CONSOLE_POLL
+	.poll_get_char	= owl_uart_poll_get_char,
+	.poll_put_char	= owl_uart_poll_put_char,
+#endif
 };
 
 #ifdef CONFIG_SERIAL_OWL_CONSOLE
-- 
2.26.2