Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762609Ab3JQTQk (ORCPT ); Thu, 17 Oct 2013 15:16:40 -0400 Received: from mail-qc0-f172.google.com ([209.85.216.172]:57443 "EHLO mail-qc0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762314Ab3JQTQi (ORCPT ); Thu, 17 Oct 2013 15:16:38 -0400 MIME-Version: 1.0 In-Reply-To: <1380074758-19808-1-git-send-email-robherring2@gmail.com> References: <1379968234-23373-1-git-send-email-robherring2@gmail.com> <1380074758-19808-1-git-send-email-robherring2@gmail.com> Date: Thu, 17 Oct 2013 14:16:37 -0500 Message-ID: Subject: Re: [PATCH v2] TTY: hvc_dcc: probe for a JTAG connection before registering From: Rob Herring To: "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Cc: Rob Herring , Paolo Pisati , Tim Gardner , Greg Kroah-Hartman , Jiri Slaby Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2491 Lines: 81 On Tue, Sep 24, 2013 at 9:05 PM, Rob Herring wrote: > From: Rob Herring > > 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 > Cc: Tim Gardner > Cc: Greg Kroah-Hartman > Cc: Jiri Slaby > Signed-off-by: Rob Herring > --- > 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/