From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754741AbcEZQ4K (ORCPT ); Thu, 26 May 2016 12:56:10 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:45616 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754660AbcEZQ4H convert rfc822-to-8bit (ORCPT ); Thu, 26 May 2016 12:56:07 -0400 Subject: Re: [PATCH v2 08/13] ACPICA: Hardware: Add optimized access bit width support To: Jan Beulich References: <5745FA2C.8020303@oracle.com> <574731DD02000078000E92FC@prv-mh.provo.novell.com> Cc: ian.jackson@eu.citrix.com, zetalog@gmail.com, len.brown@intel.com, lv.zheng@intel.com, rafael.j.wysocki@intel.com, robert.moore@intel.com, xen-devel@lists.xen.org, rjw@rjwysocki.net, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org From: Boris Ostrovsky Message-ID: <57472A95.5050100@oracle.com> Date: Thu, 26 May 2016 12:55:49 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <574731DD02000078000E92FC@prv-mh.provo.novell.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8BIT X-Source-IP: userv0021.oracle.com [156.151.31.71] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/26/2016 12:26 PM, Jan Beulich wrote: >>>> Boris Ostrovsky 05/25/16 9:17 PM >>> >> On 05/05/2016 12:58 AM, Lv Zheng wrote: >>> +static u8 >>> +acpi_hw_get_access_bit_width(struct acpi_generic_address *reg, u8 max_bit_width) >>> +{ >>> + u64 address; >>> + >>> + if (!reg->access_width) { >>> + /* >>> + * Detect old register descriptors where only the bit_width field >>> + * makes senses. The target address is copied to handle possible >>> + * alignment issues. >>> + */ >>> + ACPI_MOVE_64_TO_64(&address, ®->address); >>> + if (!reg->bit_offset && reg->bit_width && >>> + ACPI_IS_POWER_OF_TWO(reg->bit_width) && >>> + ACPI_IS_ALIGNED(reg->bit_width, 8) && >>> + ACPI_IS_ALIGNED(address, reg->bit_width)) { >>> + return (reg->bit_width); >>> + } else { >>> + if (reg->space_id == ACPI_ADR_SPACE_SYSTEM_IO) { >>> + return (32); >> This (together with "... Add access_width/bit_offset support in >> acpi_hw_write") breaks Xen guests using older QEMU which doesn't support >> 4-byte IO accesses. >> >> Why not return "reg->bit_width?:max_bit_width" ? This will preserve >> original behavior. > Did you figure out why we get here in the first place, instead of taking the > first "return"? I.e. isn't the issue the apparently wrong use of the second > ACPI_IS_ALIGNED() above? Afaict it ought to be > ACPI_IS_ALIGNED(address, reg->bit_width / 8)... We are trying to access address 0x...b004 (PM1a control) so yes, fixing alignment check would probably resolve the problem that we are seeing now. However, for compatibility purposes we may consider not doing any checks and simply return bit_width if access_width is not available. -boris