From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933704AbeAXN3t (ORCPT ); Wed, 24 Jan 2018 08:29:49 -0500 Received: from smtp.codeaurora.org ([198.145.29.96]:48982 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933556AbeAXN3r (ORCPT ); Wed, 24 Jan 2018 08:29:47 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 91DDF600C9 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=okaya@codeaurora.org Subject: Re: [PATCH v2] i2c: Allow ACPI_I2C_OPREGION if I2C is built as a module To: Mika Westerberg , Wolfram Sang Cc: Eric Auger , eric.auger.pro@gmail.com, linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org, "linux-acpi@vger.kernel.org" References: <1514988151-12248-1-git-send-email-eric.auger@redhat.com> <20180124055615.c3qwhwnj7spmcr3w@ninjato> <20180124062725.GK27654@lahna.fi.intel.com> From: Sinan Kaya Message-ID: Date: Wed, 24 Jan 2018 08:29:44 -0500 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2 MIME-Version: 1.0 In-Reply-To: <20180124062725.GK27654@lahna.fi.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org +linux-acpi On 1/24/2018 1:27 AM, Mika Westerberg wrote: > On Wed, Jan 24, 2018 at 06:56:16AM +0100, Wolfram Sang wrote: >> On Wed, Jan 03, 2018 at 03:02:31PM +0100, Eric Auger wrote: >>> If I2C is built as a module, ACPI_I2C_OPREGION cannot be set >>> and any ACPI opregion calls targeting I2C fail with no opregion found. >>> >>> This patch allows ACPI_I2C_OPREGION to be enabled both if I2C is >>> built into the kernel or built as a module. >>> >>> Signed-off-by: Eric Auger >> >> I recall that we had some discussion until ending up with the current >> solution. And I finally found it again: >> >> http://www.serverphorums.com/read.php?12,1001402 >> >> In any case, I surely want Mika's ack on any change to ACPI related >> Kconfig symbols. Adding him to CC... > > So the problem is/was that what happens if you are in a middle of BIOS > AML code touching the opregion and someone unloads the opregion handler? > If you can quarantee nothing bad happens, then I'm fine with the patch :) > Rafael to correct me if I got this right. The behavior of the operating system is well defined in the ACPI specification. Here is what I tested recently: ACPI defines _REG method to inform firmware of presence/removal of an operating region. When driver gets loaded, ACPI calls the _REG method with 1 argument. When driver gets unloaded, ACPI call the _REG method with 0 argument. Firmware can use this notification to its advantage to determine when an I2C related functionality should be accessed or not. If firmware doesn't use the _REG method, ACPI defines that AML statements accessing the operating region are ignored. You'll also see a warning from ACPICA saying the OperatingRegion 9 is no longer accessible and AML code execution failed. Also note that someone can always unbind an I2C driver from ACPI even with built-in module. I think we are talking about an orthogonal issue here. -- Sinan Kaya Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.