linux-kernel - [PATCH v2 1/1] tty: serial: owl: Add support for kernel debugger

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Message-Id: <036c09732183a30eaab230884114f65ca42ca3b9.1609865007.git.cristian.ciocaltea@gmail.com>
Date:   Tue,  5 Jan 2021 19:02:02 +0200
From:   Cristian Ciocaltea <cristian.ciocaltea@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Andreas Färber <afaerber@...e.de>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     linux-serial@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-actions@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/1] tty: serial: owl: Add support for kernel debugger

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

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...il.com>
---
Changes in v2:
 - Reverted unnecessary changes per Andreas feedback
 - Optimized implementation for 'owl_uart_poll_get_char()'
   and 'owl_uart_poll_put_char()' callbacks

 drivers/tty/serial/owl-uart.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/tty/serial/owl-uart.c b/drivers/tty/serial/owl-uart.c
index c149f8c30007..54b24669ebc5 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>
@@ -461,6 +462,26 @@ 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)
+{
+	if (owl_uart_read(port, OWL_UART_STAT) & OWL_UART_STAT_RFEM)
+		return NO_POLL_CHAR;
+
+	return owl_uart_read(port, OWL_UART_RXDAT);
+}
+
+static void owl_uart_poll_put_char(struct uart_port *port, unsigned char ch)
+{
+	while (owl_uart_read(port, OWL_UART_STAT) & OWL_UART_STAT_TFFU)
+		cpu_relax();
+
+	owl_uart_write(port, ch, OWL_UART_TXDAT);
+}
+
+#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 +497,10 @@ 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
-- 
2.30.0