tty: serial: meson_uart: Add support for kernel debugger
The kgdb invokes the poll_put_char and poll_get_char when communicating
with the host. This patch implement the serial polling hooks for the
meson_uart to be used for KGDB debugging over serial line.
Signed-off-by: Julien Masson <jmasson@baylibre.com>
Link: https://lore.kernel.org/r/867e1klo48.fsf@julienm-fedora-R90NQGV9.i-did-not-set--mail-host-address--so-tickle-me
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
index 12e1535..052c2e2 100644
--- a/drivers/tty/serial/meson_uart.c
+++ b/drivers/tty/serial/meson_uart.c
@@ -10,6 +10,7 @@
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/io.h>
+#include <linux/iopoll.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/of.h>
@@ -72,6 +73,8 @@
#define AML_UART_PORT_OFFSET 6
#define AML_UART_DEV_NAME "ttyAML"
+#define AML_UART_POLL_USEC 5
+#define AML_UART_TIMEOUT_USEC 10000
static struct uart_driver meson_uart_driver;
@@ -423,6 +426,64 @@ static void meson_uart_config_port(struct uart_port *port, int flags)
}
}
+#ifdef CONFIG_CONSOLE_POLL
+/*
+ * Console polling routines for writing and reading from the uart while
+ * in an interrupt or debug context (i.e. kgdb).
+ */
+
+static int meson_uart_poll_get_char(struct uart_port *port)
+{
+ u32 c;
+ unsigned long flags;
+
+ spin_lock_irqsave(&port->lock, flags);
+
+ if (readl(port->membase + AML_UART_STATUS) & AML_UART_RX_EMPTY)
+ c = NO_POLL_CHAR;
+ else
+ c = readl(port->membase + AML_UART_RFIFO);
+
+ spin_unlock_irqrestore(&port->lock, flags);
+
+ return c;
+}
+
+static void meson_uart_poll_put_char(struct uart_port *port, unsigned char c)
+{
+ unsigned long flags;
+ u32 reg;
+ int ret;
+
+ spin_lock_irqsave(&port->lock, flags);
+
+ /* Wait until FIFO is empty or timeout */
+ ret = readl_poll_timeout_atomic(port->membase + AML_UART_STATUS, reg,
+ reg & AML_UART_TX_EMPTY,
+ AML_UART_POLL_USEC,
+ AML_UART_TIMEOUT_USEC);
+ if (ret == -ETIMEDOUT) {
+ dev_err(port->dev, "Timeout waiting for UART TX EMPTY\n");
+ goto out;
+ }
+
+ /* Write the character */
+ writel(c, port->membase + AML_UART_WFIFO);
+
+ /* Wait until FIFO is empty or timeout */
+ ret = readl_poll_timeout_atomic(port->membase + AML_UART_STATUS, reg,
+ reg & AML_UART_TX_EMPTY,
+ AML_UART_POLL_USEC,
+ AML_UART_TIMEOUT_USEC);
+ if (ret == -ETIMEDOUT)
+ dev_err(port->dev, "Timeout waiting for UART TX EMPTY\n");
+
+out:
+ spin_unlock_irqrestore(&port->lock, flags);
+}
+
+#endif /* CONFIG_CONSOLE_POLL */
+
static const struct uart_ops meson_uart_ops = {
.set_mctrl = meson_uart_set_mctrl,
.get_mctrl = meson_uart_get_mctrl,
@@ -438,6 +499,10 @@ static const struct uart_ops meson_uart_ops = {
.request_port = meson_uart_request_port,
.release_port = meson_uart_release_port,
.verify_port = meson_uart_verify_port,
+#ifdef CONFIG_CONSOLE_POLL
+ .poll_get_char = meson_uart_poll_get_char,
+ .poll_put_char = meson_uart_poll_put_char,
+#endif
};
#ifdef CONFIG_SERIAL_MESON_CONSOLE