From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Elder Subject: Re: [PATCH] serial: 8250_dw: support high baudrates if possible Date: Tue, 01 Jul 2014 19:15:21 -0500 Message-ID: <53B34F19.9060608@linaro.org> References: <1403889920-1127-1-git-send-email-elder@linaro.org> <20140628163608.0c5536a9@alan.etchedpixels.co.uk> <53AF227C.3000102@linaro.org> <20140701230259.23f2f452@alan.etchedpixels.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ie0-f170.google.com ([209.85.223.170]:61602 "EHLO mail-ie0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752929AbaGBAPW (ORCPT ); Tue, 1 Jul 2014 20:15:22 -0400 Received: by mail-ie0-f170.google.com with SMTP id tr6so8902204ieb.29 for ; Tue, 01 Jul 2014 17:15:21 -0700 (PDT) In-Reply-To: <20140701230259.23f2f452@alan.etchedpixels.co.uk> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: One Thousand Gnomes 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 On 07/01/2014 05:02 PM, One Thousand Gnomes wrote: > 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). Yes, I acknowledged that in my earlier response. But over the weekend I decided to abandon hope that I'd be able to verify there are no problems for affected machines, and re-formulated my patch. https://lkml.org/lkml/2014/7/1/323 > 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 ? What I've done now is define a dw8250_adjustable_clk() predicate that indicates the UART baud can be adjusted by changing the clock rate. Anyone who wants to activate this functionality can just modify that function to recognize their device. -Alex > Alan >