[PATCH] TTY: hvc_dcc: probe for a JTAG connection before registering

From: Rob Herring <redacted>

Enabling the ARM DCC console and using without a JTAG connection will
simply hang the system. Since distros like to turn on all options, this
is a reoccurring problem to debug. We can do better by checking if
anything is attached and handling characters. There is no way to probe
this, so send a newline and check that it is handled.

Cc: Paolo Pisati <redacted>
Cc: Tim Gardner <redacted>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <redacted>
Signed-off-by: Rob Herring <redacted>
---
 drivers/tty/hvc/hvc_dcc.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c
index 44fbeba..44c8aff 100644
--- a/drivers/tty/hvc/hvc_dcc.c
+++ b/drivers/tty/hvc/hvc_dcc.c

@@ -86,6 +86,21 @@ static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
 	return i;
 }
 
+static bool hvc_dcc_check(void)
+{
+	unsigned long time = jiffies;
+
+	/* Write a test character to check if it is handled */
+	__dcc_putchar('\n');
+
+	while (jiffies < time + (HZ / 10)) {
+		if (!(__dcc_getstatus() & DCC_STATUS_TX))
+			return true;
+	}