From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean Delvare Subject: Re: [RFC] ACPI, APEI: Fix incorrect bit width + offset check condition Date: Thu, 14 Jun 2012 10:09:07 +0200 Message-ID: <20120614100907.3241376d@endymion.delvare> References: <1339573184-3122-1-git-send-email-hui.xiao@linux.intel.com> <20120613104651.52ce8840@endymion.delvare> <20120613174517.GA2141@us.ibm.com> <4FD98146.9060209@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from zoneX.GCU-Squad.org ([194.213.125.0]:30426 "EHLO services.gcu-squad.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753103Ab2FNIJT (ORCPT ); Thu, 14 Jun 2012 04:09:19 -0400 In-Reply-To: <4FD98146.9060209@linux.intel.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: "Xiao, Hui" Cc: Gary Hade , tony.luck@intel.com, ying.huang@intel.com, lenb@kernel.org, pluto@agmk.net, linux-acpi@vger.kernel.org, Chen Gong On Thu, 14 Jun 2012 14:14:30 +0800, Xiao, Hui wrote: > From your "good example of a valid case" above. I believe we might have different > understanding of the "Bit Width" field. > > Just to make sure, do you take "Bit Width" here(1 bit) as the bit length one should > got for mask /*after*/ shifting bit offset(31 bit) of the access_width(32 bit) > one read from the register(length unknown, or should equal to access length?) ? > > That's why you think: > bit_width + bit_offset <= *access_bit_width > is valid. I am not Gary, but it is also how I read the specification. > For me I take "Bit Width" as bits of the register for access boundary, > so I think: > (*access_bit_width <= bit_width) && (bit_offset < *access_bit_width) > is valid. > > For you above case, personally I saw you got a 1-bit register, but want to > read 32bit from it, and want to get bit[31] by shifting 31bit and mask 0x1. > > Please correct me if I am wrong. Not sure which should be the case ACPI SPEC > expected. I also have not found any specific explanation on these assumption. What makes me believe Gary is right is the granularity of each field. bit_width and bit_offset can be set with a 1-bit granularity, while access_bit_width can only be 8, 16, 32 or 64. This clearly means that access_bit_width (and Access Size before that) is a hardware thing, while bit_width and bit_offset can only be software things. You've never seen I/O ports that can be read 3 or 5 bits at a time... -- Jean Delvare