From patchwork Thu Jun 10 18:38:34 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Maciej W. Rozycki" X-Patchwork-Id: 458237 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-20.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6CBF4C48BE5 for ; Thu, 10 Jun 2021 18:38:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 54DF8613F5 for ; Thu, 10 Jun 2021 18:38:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230481AbhFJSkg (ORCPT ); Thu, 10 Jun 2021 14:40:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45000 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230508AbhFJSkf (ORCPT ); Thu, 10 Jun 2021 14:40:35 -0400 Received: from angie.orcam.me.uk (angie.orcam.me.uk [IPv6:2001:4190:8020::4]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id BD388C061574; Thu, 10 Jun 2021 11:38:38 -0700 (PDT) Received: by angie.orcam.me.uk (Postfix, from userid 500) id 1FBF79200BB; Thu, 10 Jun 2021 20:38:34 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by angie.orcam.me.uk (Postfix) with ESMTP id 19DB59200B4; Thu, 10 Jun 2021 20:38:34 +0200 (CEST) Date: Thu, 10 Jun 2021 20:38:34 +0200 (CEST) From: "Maciej W. Rozycki" To: Greg Kroah-Hartman , Jiri Slaby , Thomas Bogendoerfer cc: linux-mips@vger.kernel.org, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 2/5] serial: 8250: Actually allow UPF_MAGIC_MULTIPLIER baud rates In-Reply-To: Message-ID: References: User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Support for magic baud rate divisors of 32770 and 32769 used with SMSC Super I/O chips for extra baud rates of 230400 and 460800 respectively where base rate is 115200[1] has been added around Linux 2.5.64, which predates our repo history, but the origin could be identified as commit 2a717aad772f ("Merge with Linux 2.5.64.") with the old MIPS/Linux repo also at: . Code that is now in `serial8250_do_get_divisor' was added back then to `serial8250_get_divisor', but that code would only ever trigger if one of the higher baud rates was actually requested, and that cannot ever happen, because the earlier call to `serial8250_get_baud_rate' never returns them. This is because it calls `uart_get_baud_rate' with the maximum requested being the base rate, that is clk/16 or 115200 for SMSC chips at their nominal clock rate. Fix it then and allow UPF_MAGIC_MULTIPLIER baud rates to be selected, by requesting the maximum baud rate of clk/4 rather than clk/16 if the flag has been set. Also correct the minimum baud rate, observing that these ports only support actual (non-magic) divisors of up to 32767 only. References: [1] "FDC37M81x, PC98/99 Compliant Enhanced Super I/O Controller with Keyboard/Mouse Wake-Up", Standard Microsystems Corporation, Rev. 03/27/2000, Table 31 - "Baud Rates", p. 77 Signed-off-by: Maciej W. Rozycki Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") --- drivers/tty/serial/8250/8250_port.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) linux-serial-8250-magic-multiplier-baud-rate.diff Index: linux-malta-cbus-uart/drivers/tty/serial/8250/8250_port.c =================================================================== --- linux-malta-cbus-uart.orig/drivers/tty/serial/8250/8250_port.c +++ linux-malta-cbus-uart/drivers/tty/serial/8250/8250_port.c @@ -2659,6 +2659,21 @@ static unsigned int serial8250_get_baud_ struct ktermios *old) { unsigned int tolerance = port->uartclk / 100; + unsigned int min; + unsigned int max; + + /* + * Handle magic divisors for baud rates above baud_base on SMSC + * Super I/O chips. Enable custom rates of clk/4 and clk/8, but + * disable divisor values beyond 32767, which are unavailable. + */ + if (port->flags & UPF_MAGIC_MULTIPLIER) { + min = port->uartclk / 16 / UART_DIV_MAX >> 1; + max = (port->uartclk + tolerance) / 4; + } else { + min = port->uartclk / 16 / UART_DIV_MAX; + max = (port->uartclk + tolerance) / 16; + } /* * Ask the core to calculate the divisor for us. @@ -2666,9 +2681,7 @@ static unsigned int serial8250_get_baud_ * slower than nominal still match standard baud rates without * causing transmission errors. */ - return uart_get_baud_rate(port, termios, old, - port->uartclk / 16 / UART_DIV_MAX, - (port->uartclk + tolerance) / 16); + return uart_get_baud_rate(port, termios, old, min, max); } /*