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([2001:4898:8010:1:f0f4:7b73:eee8:a16e]) by smtp.gmail.com with ESMTPSA id f3sm10861727qkj.24.2019.02.11.12.35.13 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Feb 2019 12:35:13 -0800 (PST) From: Sinan Kaya X-Google-Original-From: Sinan Kaya Subject: Re: [PATCH v1 1/2] PCI: ATS: Add function to check ATS page aligned request status. To: "Raj, Ashok" Cc: sathyanarayanan.kuppuswamy@linux.intel.com, bhelgaas@google.com, joro@8bytes.org, dwmw2@infradead.org, linux-pci@vger.kernel.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Jacob Pan , Keith Busch References: <91bfae8b1d4b424219e3ce3c1fc03559c73f1ae7.1549478584.git.sathyanarayanan.kuppuswamy@linux.intel.com> <5d55e369-355f-b710-0594-03465aa985da@kernel.org> <32ec3293-28ea-8f0f-f801-0370b4cf0453@kernel.org> <351a1a1d-2517-5021-e7cd-99d700e17f4c@linux.intel.com> <815f2621-fc28-bff4-c300-cce7514cfe71@kernel.org> <20190211191549.GA12090@otc-nc-03> Message-ID: Date: Mon, 11 Feb 2019 15:35:13 -0500 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: <20190211191549.GA12090@otc-nc-03> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 2/11/2019 2:15 PM, Raj, Ashok wrote: > It seems rather odd we have to check for ATS version. > > I always assumed unspecified bits (Reserved) must be 0. We only check > this if ATS is enabled, and this particular bit wasn't given away for another > feature. > > Is it really required to check for ATS version before consuming this? Reading again, it looks like version check is not necessary since it is implied by the presence of this bit per this paragraph. Page Aligned Request – If Set, indicates the Untranslated Address is always aligned to a 4096 byte boundary. Setting this bit is recommended. This bit permits software to distinguish between implementations compatible with earlier version of this specification that permitted a requester to supply anything in bits [11:2].