Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752056AbaG1KrH (ORCPT ); Mon, 28 Jul 2014 06:47:07 -0400 Received: from mout.kundenserver.de ([212.227.126.187]:60668 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750778AbaG1KrE (ORCPT ); Mon, 28 Jul 2014 06:47:04 -0400 From: Arnd Bergmann To: Graeme Gregory Cc: linux-arm-kernel@lists.infradead.org, Olof Johansson , Hanjun Guo , Mark Rutland , Mark Brown , Catalin Marinas , Will Deacon , Lv Zheng , Lorenzo Pieralisi , Daniel Lezcano , Robert Moore , "linux-acpi@vger.kernel.org" , Grant Likely , Charles Garcia-Tobin , Robert Richter , Jason Cooper , Marc Zyngier , Liviu Dudau , Bjorn Helgaas , Randy Dunlap , "Rafael J. Wysocki" , "linux-kernel@vger.kernel.org" , Sudeep Holla Subject: Re: [PATCH 19/19] Documentation: ACPI for ARM64 Date: Mon, 28 Jul 2014 12:46:17 +0200 Message-ID: <5959830.lpqeqL7HbK@wuerfel> User-Agent: KMail/4.11.5 (Linux/3.11.0-18-generic; KDE/4.11.5; x86_64; ; ) In-Reply-To: <53D616AD.2090501@linaro.org> References: <1406206825-15590-1-git-send-email-hanjun.guo@linaro.org> <5014834.k6eecMddPC@wuerfel> <53D616AD.2090501@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-Provags-ID: V02:K0:v1x/djs+a5gMy6XNwXJ0nfHNNR+IKhwQKBwuxSIyyDu XvuysoopGBKy4EFoFDLc32jWQnm13ssjg72tsbmaTmyTYwc5nm nWabvFXTFAZsFKIhq5rqHRB3ZjzqLuijNAWRHUJUYRap9R30qa z7/k+aWJp9gu9NPN0+XSTFt9K6zqZ/e9ZEOJz5p4Ob7NlwTwdo p3pli6t1k1gKQWBgoLdEOUxWsjsIxzbKKQI5tek5lcS27Lfu6Q +plTh5MM53NC4BqYKXRpWlT15LU6iZv9Xi6kUJNkJ84iy5ZZ8l QB8eFf86hjaA3+3uUlh3WdcLbQP6BLL4CX1BAuqU9cMWligfBt z1XhQmo/KGrnr2hJwnhI= Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Monday 28 July 2014 10:23:57 Graeme Gregory wrote: > The PL011 UART is the use-case I keep hitting, that IP block has a > variable input clock on pretty much everything I have seen in the wild. Ok, I see. What does ACPI-5.1 say about pl011? Interestingly, the subset of pl011 that is specified by SBSA does not contain the IBRD/FBRD registers, effectively making it a fixed-rated UART (I guess that would be a ART, without the U then), and you consequently don't even need to know the clock rate. However, my guess is that most hardware in the real world contains an actual pl011 and it does make a lot of sense to allow setting the baud rate on it, which then requires knowing the input clock. If there is any hardware that implements just the SBSA-mandated subset rather than the full pl011, we should probably implement both in the kernel: a dumb driver that can only send and receive, and the more complex one that can set the bit rates and flow-control but that requires a standardized ACPI table with the input clock rate. Whether the two would belong into one file or two separate driver modules is something I can't tell, it would be up to the serial maintainers to decide. > I really hope that this use does not spread beyond a few essential > devices like the UART. IMO all real hardware should be the other side of > a PCIe bridge. I would definitely agree with that. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/