forked from Minki/linux
TTY: hvc_dcc: probe for a JTAG connection before registering
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>
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@ -86,6 +86,21 @@ static int hvc_dcc_get_chars(uint32_t vt, char *buf, int count)
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return i;
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}
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static bool hvc_dcc_check(void)
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{
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unsigned long time = jiffies + (HZ / 10);
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/* Write a test character to check if it is handled */
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__dcc_putchar('\n');
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while (time_is_after_jiffies(time)) {
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if (!(__dcc_getstatus() & DCC_STATUS_TX))
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return true;
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}
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return false;
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}
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static const struct hv_ops hvc_dcc_get_put_ops = {
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.get_chars = hvc_dcc_get_chars,
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.put_chars = hvc_dcc_put_chars,
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@ -93,6 +108,9 @@ static const struct hv_ops hvc_dcc_get_put_ops = {
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static int __init hvc_dcc_console_init(void)
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{
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if (!hvc_dcc_check())
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return -ENODEV;
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hvc_instantiate(0, 0, &hvc_dcc_get_put_ops);
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return 0;
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}
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@ -100,6 +118,9 @@ console_initcall(hvc_dcc_console_init);
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static int __init hvc_dcc_init(void)
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{
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if (!hvc_dcc_check())
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return -ENODEV;
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hvc_alloc(0, 0, &hvc_dcc_get_put_ops, 128);
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return 0;
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}
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