Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934202AbbGHL4F (ORCPT ); Wed, 8 Jul 2015 07:56:05 -0400 Received: from mail-qk0-f172.google.com ([209.85.220.172]:35334 "EHLO mail-qk0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932897AbbGHLz7 (ORCPT ); Wed, 8 Jul 2015 07:55:59 -0400 Message-ID: <559D0FCC.5040107@hurleysoftware.com> Date: Wed, 08 Jul 2015 07:55:56 -0400 From: Peter Hurley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Taichi Kageyama , "gregkh@linuxfoundation.org" CC: "linux-serial@vger.kernel.org" , "jslaby@suse.cz" , "linux-kernel@vger.kernel.org" , "prarit@redhat.com" , Naoya Horiguchi Subject: Re: [PATCH 2/2] serial: 8250: Allow to skip autoconfig_irq() for a console References: <55717224.9060104@cp.jp.nec.com> <557173EC.5000307@cp.jp.nec.com> In-Reply-To: <557173EC.5000307@cp.jp.nec.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4837 Lines: 115 Hi Taichi, On 06/05/2015 06:03 AM, Taichi Kageyama wrote: > This patch provides a new parameter as a workaround of the following > problem. It allows us to skip autoconfig_irq() and to use a well-known irq > number for a console even if CONFIG_SERIAL_8250_DETECT_IRQ is defined. > > There're cases where autoconfig_irq() fails during boot. > In these cases, the console doesn't work in interrupt mode, > the mode cannot be changed anymore, and "input overrun" > (which can make operation mistakes) happens easily. > This problem happens with high rate every boot once it occurs > because the boot sequence is always almost same. > > autoconfig_irq() assumes that a CPU can handle an interrupt from a serial > during the waiting time, but there're some cases where the CPU cannot > handle the interrupt for longer than the time. It completely depends on > how other functions work on the CPU. Ideally, autoconfig_irq() should be > fixed It completely depends on how long some other driver has interrupts disabled, which is a problem that needs fixed _in that driver_. autoconfig_irq() does not need fixing. A typical cause of this behavior is printk spew from overly-instrumented debugging of some driver (trace_printk is better suited to heavy instrumentation). Regards, Peter Hurley > to control these cases but as long as auto_irq algorithm is used, > it's hard to know which CPU can handle an interrupt from a serial and > to assure the interrupt of the CPU is enabled during auto_irq. > Meanwhile for legacy consoles, they actually don't require auto_irq > because they basically use well-known irq number. > For non-console serials, this workaround is not required > because setserial command can kick autoconfig_irq() again for them. > > Signed-off-by: Taichi Kageyama > Cc: Naoya Horiguchi > --- > drivers/tty/serial/8250/8250_core.c | 17 +++++++++++++++++ > 1 files changed, 17 insertions(+), 0 deletions(-) > > diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c > index 6bf31f2..60fda28 100644 > --- a/drivers/tty/serial/8250/8250_core.c > +++ b/drivers/tty/serial/8250/8250_core.c > @@ -65,6 +65,8 @@ static int serial_index(struct uart_port *port) > > static unsigned int skip_txen_test; /* force skip of txen test at init time */ > > +static unsigned int skip_cons_autoirq; /* force skip autoirq for console */ > + > /* > * Debugging. > */ > @@ -3336,6 +3338,9 @@ serial8250_register_ports(struct uart_driver *drv, struct device *dev) > if (skip_txen_test) > up->port.flags |= UPF_NO_TXEN_TEST; > > + if (uart_console(&up->port) && skip_cons_autoirq) > + up->port.flags &= ~UPF_AUTO_IRQ; > + > uart_add_one_port(drv, &up->port); > } > } > @@ -3875,6 +3880,9 @@ int serial8250_register_8250_port(struct uart_8250_port *up) > if (skip_txen_test) > uart->port.flags |= UPF_NO_TXEN_TEST; > > + if (uart_console(&uart->port) && skip_cons_autoirq) > + uart->port.flags &= ~UPF_AUTO_IRQ; > + > if (up->port.flags & UPF_FIXED_TYPE) > uart->port.type = up->port.type; > > @@ -3936,6 +3944,10 @@ void serial8250_unregister_port(int line) > uart->port.flags &= ~UPF_BOOT_AUTOCONF; > if (skip_txen_test) > uart->port.flags |= UPF_NO_TXEN_TEST; > + > + if (uart_console(&uart->port) && skip_cons_autoirq) > + uart->port.flags &= ~UPF_AUTO_IRQ; > + > uart->port.type = PORT_UNKNOWN; > uart->port.dev = &serial8250_isa_devs->dev; > uart->capabilities = 0; > @@ -4044,6 +4056,9 @@ MODULE_PARM_DESC(nr_uarts, "Maximum number of UARTs supported. (1-" __MODULE_STR > module_param(skip_txen_test, uint, 0644); > MODULE_PARM_DESC(skip_txen_test, "Skip checking for the TXEN bug at init time"); > > +module_param(skip_cons_autoirq, uint, 0644); > +MODULE_PARM_DESC(skip_cons_autoirq, "Skip auto irq for console during boot"); > + > #ifdef CONFIG_SERIAL_8250_RSA > module_param_array(probe_rsa, ulong, &probe_rsa_count, 0444); > MODULE_PARM_DESC(probe_rsa, "Probe I/O ports for RSA"); > @@ -4070,6 +4085,8 @@ static void __used s8250_options(void) > module_param_cb(share_irqs, ¶m_ops_uint, &share_irqs, 0644); > module_param_cb(nr_uarts, ¶m_ops_uint, &nr_uarts, 0644); > module_param_cb(skip_txen_test, ¶m_ops_uint, &skip_txen_test, 0644); > + module_param_cb(skip_cons_autoirq, ¶m_ops_uint, > + &skip_cons_autoirq, 0644); > #ifdef CONFIG_SERIAL_8250_RSA > __module_param_call(MODULE_PARAM_PREFIX, probe_rsa, > ¶m_array_ops, .arr = &__param_arr_probe_rsa, > -- 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/