Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964832AbWEBN6q (ORCPT ); Tue, 2 May 2006 09:58:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964806AbWEBN6q (ORCPT ); Tue, 2 May 2006 09:58:46 -0400 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:43223 "EHLO lxorguk.ukuu.org.uk") by vger.kernel.org with ESMTP id S964832AbWEBN6p (ORCPT ); Tue, 2 May 2006 09:58:45 -0400 Subject: PATCH (RFC): Rework the 8250 console fix From: Alan Cox To: rmk@arm.linux.org.uk, linux-kernel@vger.kernel.org Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Tue, 02 May 2006 15:09:43 +0100 Message-Id: <1146578983.3519.49.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-4.fc4) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2211 Lines: 67 Russell got various bits of mail showing the 8250 console fix broke some setups with the assumptions it made. Based on this suggestion that we actually need to just do the locking I've prepared an alternative patch. The patch does one thing a little oddly. If an oops is in progress it only attempts to take the port lock and continues regardless. In that situation the oops will hit the console but things may be a bit odd thereafter. Getting the oops out seems to be the important thing to do in that situation. There are two questions that I think make this an RFC not a final patch 1. Should this be pushed up into serial/serial_core.c for all chips. 2. Is the use of local_irq_save/spin_trylock spin_unlock_irqrestore going to break any platforms that do weird stuff or do we need a spin_trylock_irqsave ? Alan (no signed off by as it isn't yet appropriate to merge.. and if I don't sign it off nobody can jump the gun 8)) --- drivers/serial/8250.c~ 2006-05-02 14:28:05.430397240 +0100 +++ drivers/serial/8250.c 2006-05-02 14:28:05.430397240 +0100 @@ -2201,7 +2201,18 @@ { struct uart_8250_port *up = &serial8250_ports[co->index]; unsigned int ier; + unsigned long flags; + int locked = 1; + if (unlikely(oops_in_progress)) { + /* We want our private lock to be ignored during an oops. This + might cause a serial console stall afterwards but the oops data + is the critical information to get out */ + local_irq_save(flags); + locked = spin_trylock(&up->port.lock); + } else + spin_lock_irqsave(&up->port.lock, flags); + touch_nmi_watchdog(); /* @@ -2221,8 +2232,12 @@ * and restore the IER */ wait_for_xmitr(up, BOTH_EMPTY); - up->ier |= UART_IER_THRI; - serial_out(up, UART_IER, ier | UART_IER_THRI); + serial_out(up, UART_IER, ier); + + if (locked) + spin_unlock_irqrestore(&up->port.lock, flags); + else + local_irq_restore(flags); } static int serial8250_console_setup(struct console *co, char *options) - 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/