linux-kernel - Re: [PATCH v2] TTY: hvc_dcc: probe for a JTAG connection before registering

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Date:	Thu, 17 Oct 2013 14:16:37 -0500
From:	Rob Herring <robherring2@...il.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Cc:	Rob Herring <rob.herring@...xeda.com>,
	Paolo Pisati <paolo.pisati@...onical.com>,
	Tim Gardner <tim.gardner@...onical.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH v2] TTY: hvc_dcc: probe for a JTAG connection before registering

On Tue, Sep 24, 2013 at 9:05 PM, Rob Herring <robherring2@...il.com> wrote:
> From: Rob Herring <rob.herring@...xeda.com>
>
> 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@...onical.com>
> Cc: Tim Gardner <tim.gardner@...onical.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Jiri Slaby <jslaby@...e.cz>
> Signed-off-by: Rob Herring <rob.herring@...xeda.com>
> ---
> v2: use time_is_after_jiffies
>
>  drivers/tty/hvc/hvc_dcc.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)

Greg, Jiri,

Can you please apply.

Rob

>
> diff --git a/drivers/tty/hvc/hvc_dcc.c b/drivers/tty/hvc/hvc_dcc.c
> index 44fbeba..3502a7b 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 + (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;
>  }
> --
> 1.8.1.2
>
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