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[109.252.193.102]) by smtp.googlemail.com with ESMTPSA id 2sm914499ljf.61.2021.04.27.22.44.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Apr 2021 22:44:18 -0700 (PDT) Subject: Re: [PATCH v2 0/5] iommu: Support identity mappings of reserved-memory regions To: Krishna Reddy , Thierry Reding , Joerg Roedel , Rob Herring References: <20210423163234.3651547-1-thierry.reding@gmail.com> <869ec3a2-26df-2ce8-bd21-b681d6ef3985@gmail.com> From: Dmitry Osipenko Message-ID: Date: Wed, 28 Apr 2021 08:44:17 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US Cc: "devicetree@vger.kernel.org" , Will Deacon , "iommu@lists.linux-foundation.org" , Nicolin Chen , "linux-tegra@vger.kernel.org" , Robin Murphy X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; 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[109.252.193.102]) by smtp.googlemail.com with ESMTPSA id 2sm914499ljf.61.2021.04.27.22.44.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Apr 2021 22:44:18 -0700 (PDT) Subject: Re: [PATCH v2 0/5] iommu: Support identity mappings of reserved-memory regions To: Krishna Reddy , Thierry Reding , Joerg Roedel , Rob Herring Cc: Will Deacon , Robin Murphy , Nicolin Chen , "devicetree@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "linux-tegra@vger.kernel.org" References: <20210423163234.3651547-1-thierry.reding@gmail.com> <869ec3a2-26df-2ce8-bd21-b681d6ef3985@gmail.com> From: Dmitry Osipenko Message-ID: Date: Wed, 28 Apr 2021 08:44:17 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-tegra@vger.kernel.org 27.04.2021 21:30, Krishna Reddy пишет: >> Is it always safe to enable SMMU ASID in a middle of a DMA request made by a >> memory client? > > From MC point of view, It is safe to enable and has been this way from many years in downstream code for display engine. > It doesn't impact the transactions that have already bypassed SMMU before enabling SMMU ASID. > Transactions that are yet to pass SMMU stage would go through SMMU once SMMU ASID is enabled and visible. Hello, Thank you for the answer. Could you please give more information about: 1) Are you on software or hardware team, or both? 2) Is SMMU a third party IP or developed in-house? 3) Do you have a direct access to HDL sources? Are you 100% sure that hardware does what you say? 4) What happens when CPU writes to ASID register? Does SMMU state machine latch ASID status (making it visible) only at a single "safe" point?