From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932734AbaIEOiJ (ORCPT ); Fri, 5 Sep 2014 10:38:09 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:45389 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757144AbaIEOiG (ORCPT ); Fri, 5 Sep 2014 10:38:06 -0400 Message-ID: <5409CA9E.2060807@arm.com> Date: Fri, 05 Sep 2014 15:37:18 +0100 From: Andre Przywara Organization: ARM Ltd. User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0 MIME-Version: 1.0 To: Rob Herring , Arnd Bergmann CC: "linux-arm-kernel@lists.infradead.org" , Russell King , Greg Kroah-Hartman , LKML , "linux-serial@vger.kernel.org" , Jiri Slaby Subject: Re: [RFC PATCH 1/1] drivers: introduce ARM SBSA generic UART driver References: <1409328803-1953-1-git-send-email-andre.przywara@arm.com> <540596A6.8000608@arm.com> <3749748.k4a1nSHDdj@wuerfel> In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Rob, On 02/09/14 18:38, Rob Herring wrote: > On Tue, Sep 2, 2014 at 8:48 AM, Arnd Bergmann wrote: >> On Tuesday 02 September 2014 08:20:53 Rob Herring wrote: >>>>> >>>>> This alone is not okay. There is no such implementation of hardware. >>>> >>>> But the SBSA explicitly allows this. I don't know of any vendor who just >>>> implements the subset, but I've been told that this has been asked for. >>> >>> To use baudrate as an example, that must be configurable somehow >>> either with pl011 registers or in a vendor specific way. I suppose you >>> could do an actual implementation with all those things hardcoded in >>> the design, but that seems unlikely. >> >> Why does the baudrate need to be configurable? I think it's completely >> reasonable to specify a console port that has a fixed (as in the >> OS must not care) rate, and that can be implemented either as a UART >> with a programmable rate or as a set of registers that directly talks >> to a remote system management device over whatever hardware protocol >> they choose. > > Sure. It is also completely reasonable that baudrate is configurable > and vendors can implement it however they choose since the SBSA does > not specify it. But this would be a different driver for a different hardware then and not covered by the SBSA version - so to some degree not our problem ;-) I don't see how we could really cover this problem for every possibly upcoming implementation. If I got the spec correctly, then exposing the baudrate setting for SBSA hardware is not meaningful in the sense of the spec. If you want to go with a configurable UART complying to the spec, you'd probably use a full featured PL011. > IIRC, the enabling and disabling bits are not > specified either. Correct, also the FIFO is always on and the word format is fixed to 8n1. Regards, Andre. > > Not having configurability is simply one variation on possible implementations. > > Rob >