TTY: hvc_dcc: probe for a JTAG connection before registering (f377775d) · Commits · 戴 / test

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 <paolo.pisati@canonical.com> Cc: Tim Gardner <tim.gardner@canonical.com> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jiri Slaby <jslaby@suse.cz> Signed-off-by:

Rob Herring <rob.herring@calxeda.com> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/hvc/hvc_dcc.c

+21 −0

Original line number	Diff line number	Diff line
		@@ -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 + (HZ / 10);

		/* Write a test character to check if it is handled */
		__dcc_putchar('\n');

		while (time_is_after_jiffies(time)) {
		if (!(__dcc_getstatus() & DCC_STATUS_TX))
		return true;
		}

		return false;
		}

		static const struct hv_ops hvc_dcc_get_put_ops = {
		.get_chars = hvc_dcc_get_chars,
		.put_chars = hvc_dcc_put_chars,
		@@ -93,6 +108,9 @@ static const struct hv_ops hvc_dcc_get_put_ops = {

		static int __init hvc_dcc_console_init(void)
		{
		if (!hvc_dcc_check())
		return -ENODEV;

		hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
		return 0;
		}
		@@ -100,6 +118,9 @@ console_initcall(hvc_dcc_console_init);

		static int __init hvc_dcc_init(void)
		{
		if (!hvc_dcc_check())
		return -ENODEV;

		hvc_alloc(0, 0, &hvc_dcc_get_put_ops, 128);
		return 0;
		}

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