From owner-svn-src-head@freebsd.org Mon Apr 13 20:43:57 2020 Return-Path: Delivered-To: svn-src-head@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 9A2FA2A8C57; Mon, 13 Apr 2020 20:43:57 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) server-signature RSA-PSS (4096 bits) client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 491LF93gHNz4BQq; Mon, 13 Apr 2020 20:43:57 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 78FC8217A9; Mon, 13 Apr 2020 20:43:57 +0000 (UTC) (envelope-from jhb@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id 03DKhv0o054620; Mon, 13 Apr 2020 20:43:57 GMT (envelope-from jhb@FreeBSD.org) Received: (from jhb@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id 03DKhvE5054619; Mon, 13 Apr 2020 20:43:57 GMT (envelope-from jhb@FreeBSD.org) Message-Id: <202004132043.03DKhvE5054619@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: jhb set sender to jhb@FreeBSD.org using -f From: John Baldwin Date: Mon, 13 Apr 2020 20:43:57 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r359899 - head/sys/dev/uart X-SVN-Group: head X-SVN-Commit-Author: jhb X-SVN-Commit-Paths: head/sys/dev/uart X-SVN-Commit-Revision: 359899 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 13 Apr 2020 20:43:57 -0000 Author: jhb Date: Mon Apr 13 20:43:57 2020 New Revision: 359899 URL: https://svnweb.freebsd.org/changeset/base/359899 Log: Correct baud rate error calculation. Shifting right by 1 is not the same as dividing by 2 for signed values. In particular, dividing a signed value by 2 gives the integer ceiling of the (e.g. -5 / 2 == -2) whereas shifting right by 1 always gives the floor (-5 >> 1 == -3). An embedded board with a 25 Mhz base clock results in an error of -30.5% when used with a baud rate of 115200. Using division, this truncates to -30% and is permitted. Using the shift, this fails and is rejected causing TIOCSETA requests to fail with EINVAL and breaking getty(8). Using division gives the same error range for both over and under baud rates and also makes the code match the behavior documented in the existing comment about supporting boards with 25 Mhz clocks. Reported by: imp MFC after: 2 weeks Sponsored by: DARPA Differential Revision: https://reviews.freebsd.org/D24367 Modified: head/sys/dev/uart/uart_dev_ns8250.c Modified: head/sys/dev/uart/uart_dev_ns8250.c ============================================================================== --- head/sys/dev/uart/uart_dev_ns8250.c Mon Apr 13 20:25:01 2020 (r359898) +++ head/sys/dev/uart/uart_dev_ns8250.c Mon Apr 13 20:43:57 2020 (r359899) @@ -139,7 +139,7 @@ ns8250_divisor(int rclk, int baudrate) actual_baud = rclk / (divisor << 4); /* 10 times error in percent: */ - error = ((actual_baud - baudrate) * 2000 / baudrate + 1) >> 1; + error = ((actual_baud - baudrate) * 2000 / baudrate + 1) / 2; /* enforce maximum error tolerance: */ if (error < -UART_DEV_TOLERANCE_PCT || error > UART_DEV_TOLERANCE_PCT)