From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755956AbZKRKIK (ORCPT ); Wed, 18 Nov 2009 05:08:10 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752434AbZKRKIJ (ORCPT ); Wed, 18 Nov 2009 05:08:09 -0500 Received: from cantor2.suse.de ([195.135.220.15]:42506 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752292AbZKRKIH (ORCPT ); Wed, 18 Nov 2009 05:08:07 -0500 Date: Wed, 18 Nov 2009 11:08:11 +0100 (CET) From: Jiri Kosina X-X-Sender: jkosina@wotan.suse.de To: Alan Cox , Andrew Morton , Greg Kroah-Hartman Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Markus Armbruster , Ian Jackson , Michal Hocko Subject: [PATCH] Do not read IIR in serial8250_start_tx when UART_BUG_TXEN Message-ID: User-Agent: Alpine 2.00 (LSU 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The patch below has been lost several times (the last submission happened probably on [1]). I am currently aware of a real hardware which triggers this problem quite reliably, so we should rather have that really fixed. [1] http://lkml.org/lkml/2009/3/12/379 From: Ian Jackson Do not read IIR in serial8250_start_tx when UART_BUG_TXEN Reading the IIR clears some oustanding interrupts so it is not safe. Instead, simply transmit immediately if the buffer is empty without regard to IIR. Signed-off-by: Ian Jackson Reviewed-by: Markus Armbruster Reviewed-by: Jiri Kosina --- drivers/serial/8250.c | 8 +++----- 1 files changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c index 737b4c9..807042b 100644 --- a/drivers/serial/8250.c +++ b/drivers/serial/8250.c @@ -1339,14 +1339,12 @@ static void serial8250_start_tx(struct uart_port *port) serial_out(up, UART_IER, up->ier); if (up->bugs & UART_BUG_TXEN) { - unsigned char lsr, iir; + unsigned char lsr; lsr = serial_in(up, UART_LSR); up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS; - iir = serial_in(up, UART_IIR) & 0x0f; if ((up->port.type == PORT_RM9000) ? - (lsr & UART_LSR_THRE && - (iir == UART_IIR_NO_INT || iir == UART_IIR_THRI)) : - (lsr & UART_LSR_TEMT && iir & UART_IIR_NO_INT)) + (lsr & UART_LSR_THRE) : + (lsr & UART_LSR_TEMT)) transmit_chars(up); } }