From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030315AbaGAWDZ (ORCPT ); Tue, 1 Jul 2014 18:03:25 -0400 Received: from lxorguk.ukuu.org.uk ([81.2.110.251]:57883 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965073AbaGAWDW (ORCPT ); Tue, 1 Jul 2014 18:03:22 -0400 Date: Tue, 1 Jul 2014 23:02:59 +0100 From: One Thousand Gnomes To: Alex Elder Cc: gregkh@linuxfoundation.org, heikki.krogerus@linux.intel.com, david.daney@cavium.com, loic.poulain@intel.com, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] serial: 8250_dw: support high baudrates if possible Message-ID: <20140701230259.23f2f452@alan.etchedpixels.co.uk> In-Reply-To: <53AF227C.3000102@linaro.org> References: <1403889920-1127-1-git-send-email-elder@linaro.org> <20140628163608.0c5536a9@alan.etchedpixels.co.uk> <53AF227C.3000102@linaro.org> Organization: Intel Corporation X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.23; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 28 Jun 2014 15:15:56 -0500 Alex Elder wrote: > On 06/28/2014 10:36 AM, One Thousand Gnomes wrote: > > On Fri, 27 Jun 2014 12:25:20 -0500 > >> + rate = 16 * max(115200U, (unsigned int)baud); > >> + > > > > This assumes an arbitarily configurable clock, which is not I think the > > usual case. > > If the clock's rate can't change, this will return an error, > and the recorded rate (p->uartclk) will not be changed. Which assumes an arbitrarily configurable clock, whereas you want to find the correct clock and multiplier combination for the baud rate. Most of these ports are wired to fixed clocks (which is fine) or clocks with limited numbers of supported frequencies (which is not). Your patch is an improvement but doesn't really fix the overall problem. If we have enough devices with variable clocks for it to be useful then fine - but can we merge it with a big FIXME note so that whoever comes along wondering why their clock doesn't work or behaves very oddly can figure it out and fix that case ? Alan