Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753177AbaG2JCV (ORCPT ); Tue, 29 Jul 2014 05:02:21 -0400 Received: from mail-pa0-f47.google.com ([209.85.220.47]:46663 "EHLO mail-pa0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753105AbaG2JCR (ORCPT ); Tue, 29 Jul 2014 05:02:17 -0400 Message-ID: <53D762CD.7070006@linaro.org> Date: Tue, 29 Jul 2014 17:01:01 +0800 From: Hanjun Guo User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Arnd Bergmann , Olof Johansson CC: linux-arm-kernel@lists.infradead.org, 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 , Graeme Gregory , Randy Dunlap , "Rafael J. Wysocki" , "linux-kernel@vger.kernel.org" , Sudeep Holla Subject: Re: [PATCH 19/19] Documentation: ACPI for ARM64 References: <1406206825-15590-1-git-send-email-hanjun.guo@linaro.org> <1406206825-15590-20-git-send-email-hanjun.guo@linaro.org> <5014834.k6eecMddPC@wuerfel> In-Reply-To: <5014834.k6eecMddPC@wuerfel> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2014-7-28 17:07, Arnd Bergmann wrote: > On Saturday 26 July 2014 19:34:48 Olof Johansson wrote: >> On Thu, Jul 24, 2014 at 6:00 AM, Hanjun Guo wrote: >>> +Relationship with Device Tree >>> +----------------------------- >>> + >>> +ACPI support in drivers and subsystems for ARMv8 should never be mutually >>> +exclusive with DT support at compile time. >>> + >>> +At boot time the kernel will only use one description method depending on >>> +parameters passed from the bootloader. >> >> Possibly overriden by kernel bootargs. And as debated for quite a >> while earlier this year, acpi should still default to off -- if a DT >> and ACPI are both passed in, DT should at this time be given priority. > > I think this would be harder to do with the way that ACPI is passed in > to the kernel. IIRC, you always have a minimal DT information based on > the ARM64 boot protocol, but in the case of ACPI, this contains pointers > to the ACPI tables, which are then used for populating the Linux platform > devices (unless acpi=disabled is set), while the other contents of the > DTB may be present but we skip the of_platform_populate state. > > If this is correct, then replacing the firmware-generated dtb with a > user-provided on would implicitly remove the ACPI tables from visibility, > which is exactly what we want. > > It's possible that I'm misremembering it though, and it should be > documented better. > >>> +Regardless of whether DT or ACPI is used, the kernel must always be capable >>> +of booting with either scheme. >> >> It should always be possible to compile out ACPI. There will be plenty >> of platforms that will not implement it, so disabling CONFIG_ACPI >> needs to be possible. > > Right. Actually, if platforms don't implement ACPI, acpi_disabled will always be set to 1 at early boot stage which before the device tree is unflattened, so device tree will work as expected even if CONFIG_ACPI=y on such platforms. Thanks Hanjun -- 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/