Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760912AbZFXRWm (ORCPT ); Wed, 24 Jun 2009 13:22:42 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755295AbZFXRWe (ORCPT ); Wed, 24 Jun 2009 13:22:34 -0400 Received: from mx2.redhat.com ([66.187.237.31]:34161 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753524AbZFXRWe (ORCPT ); Wed, 24 Jun 2009 13:22:34 -0400 Date: Wed, 24 Jun 2009 13:22:26 -0400 From: Dave Jones To: alan@lxorguk.ukuu.org.uk Cc: Linux Kernel , Mathias Adam Subject: serial: enable higher baud rates for 16c95x Message-ID: <20090624172213.GA21123@redhat.com> Mail-Followup-To: Dave Jones , alan@lxorguk.ukuu.org.uk, Linux Kernel , Mathias Adam MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2809 Lines: 86 This patch has been around (and in Fedora) for 4 years. Previous discussion around this patch: http://marc.theaimsgroup.com/?l=linux-kernel&m=112687270832687&w=2 https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=126403 http://lkml.org/lkml/2006/8/2/208 The objection seemed to be summarised as "it might break something else". In the four years it's been in Fedora, I don't recall seeing a single serial bug report that was related. From: Mathias Adam Signed-off-by: Dave Jones --- linux-2.6.13-org/drivers/serial/8250.c 2005-08-29 01:41:01.000000000 +0200 +++ linux-2.6.13/drivers/serial/8250.c 2005-09-16 12:18:14.000000000 +0200 @@ -7,6 +7,9 @@ * * Copyright (C) 2001 Russell King. * + * 2005/09/16: Enabled higher baud rates for 16C95x. + * (Mathias Adam ) + * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or @@ -1652,6 +1655,14 @@ else if ((port->flags & UPF_MAGIC_MULTIPLIER) && baud == (port->uartclk/8)) quot = 0x8002; + /* + * For 16C950s UART_TCR is used in combination with divisor==1 + * to achieve baud rates up to baud_base*4. + */ + else if ((port->type == PORT_16C950) && + baud > (port->uartclk/16)) + quot = 1; + else quot = uart_get_divisor(port, baud); @@ -1665,7 +1676,7 @@ struct uart_8250_port *up = (struct uart_8250_port *)port; unsigned char cval, fcr = 0; unsigned long flags; - unsigned int baud, quot; + unsigned int baud, quot, max_baud; switch (termios->c_cflag & CSIZE) { case CS5: @@ -2034,7 +2034,8 @@ serial8250_set_termios(struct uart_port /* * Ask the core to calculate the divisor for us. */ - baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16); + max_baud = (up->port.type == PORT_16C950 ? port->uartclk/4 : port->uartclk/16); + baud = uart_get_baud_rate(port, termios, old, 0, max_baud); quot = serial8250_get_divisor(port, baud); /* @@ -1733,6 +1745,19 @@ */ spin_lock_irqsave(&up->port.lock, flags); + /* + * 16C950 supports additional prescaler ratios between 1:16 and 1:4 + * thus increasing max baud rate to uartclk/4. + */ + if (up->port.type == PORT_16C950) { + if (baud == port->uartclk/4) + serial_icr_write(up, UART_TCR, 0x4); + else if (baud == port->uartclk/8) + serial_icr_write(up, UART_TCR, 0x8); + else + serial_icr_write(up, UART_TCR, 0); + } + /* * Update the per-port timeout. */ -- 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/