From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933782Ab0BQAMH (ORCPT ); Tue, 16 Feb 2010 19:12:07 -0500 Received: from kroah.org ([198.145.64.141]:41532 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933756Ab0BQAMA (ORCPT ); Tue, 16 Feb 2010 19:12:00 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Dick Hollenbeck , Alan Cox , Kees Schoenmakers , Andrew Morton , stable , Greg Kroah-Hartman Subject: [PATCH 1/1] serial: 8250: add serial transmitter fully empty test Date: Tue, 16 Feb 2010 16:11:57 -0800 Message-Id: <1266365517-32131-1-git-send-email-gregkh@suse.de> X-Mailer: git-send-email 1.6.4.2 In-Reply-To: <20100217000217.GC31137@kroah.com> References: <20100217000217.GC31137@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dick Hollenbeck When controlling an industrial radio modem it can be necessary to manipulate the handshake lines in order to control the radio modem's transmitter, from userspace. The transmitter should not be turned off before all characters have been transmitted. serial8250_tx_empty() was reporting that all characters were transmitted before they actually were. === Discovered in parallel with more testing and analysis by Kees Schoenmakers as follows: I ran into an NetMos 9835 serial pci board which behaves a little different than the standard. This type of expansion board is very common. "Standard" 8250 compatible devices clear the 'UART_LST_TEMT" bit together with the "UART_LSR_THRE" bit when writing data to the device. The NetMos device does it slightly different I believe that the TEMT bit is coupled to the shift register. The problem is that after writing data to the device and very quickly after that one does call serial8250_tx_empty, it returns the wrong information. My patch makes the test more robust (and solves the problem) and it does not affect the already correct devices. Alan: We may yet need to quirk this but now we know which chips we have a way to do that should we find this breaks some other 8250 clone with dodgy THRE. Signed-off-by: Dick Hollenbeck Signed-off-by: Alan Cox Cc: Kees Schoenmakers Signed-off-by: Andrew Morton Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/serial/8250.c | 7 ++++--- 1 files changed, 4 insertions(+), 3 deletions(-) diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c index c3e37c8..e9b15c3 100644 --- a/drivers/serial/8250.c +++ b/drivers/serial/8250.c @@ -83,6 +83,9 @@ static unsigned int skip_txen_test; /* force skip of txen test at init time */ #define PASS_LIMIT 256 +#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE) + + /* * We default to IRQ0 for the "no irq" hack. Some * machine types want others as well - they're free @@ -1792,7 +1795,7 @@ static unsigned int serial8250_tx_empty(struct uart_port *port) up->lsr_saved_flags |= lsr & LSR_SAVE_FLAGS; spin_unlock_irqrestore(&up->port.lock, flags); - return lsr & UART_LSR_TEMT ? TIOCSER_TEMT : 0; + return (lsr & BOTH_EMPTY) == BOTH_EMPTY ? TIOCSER_TEMT : 0; } static unsigned int serial8250_get_mctrl(struct uart_port *port) @@ -1850,8 +1853,6 @@ static void serial8250_break_ctl(struct uart_port *port, int break_state) spin_unlock_irqrestore(&up->port.lock, flags); } -#define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE) - /* * Wait for transmitter & holding register to empty */ -- 1.7.0