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[47.54.130.67]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8ed54eb91a0sm52800285a.47.2026.04.20.05.40.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Apr 2026 05:40:33 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1wEnvU-0000000CImY-0bzn; Mon, 20 Apr 2026 09:40:32 -0300 Date: Mon, 20 Apr 2026 09:40:32 -0300 From: Jason Gunthorpe To: Evangelos Petrongonas Cc: Will Deacon , Robin Murphy , Joerg Roedel , Nicolin Chen , Pranjal Shrivastava , Lu Baolu , linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, nh-open-source@amazon.com, Zeev Zilberman Subject: Re: [PATCH] iommu/arm-smmu-v3: Allow disabling Stage 1 translation Message-ID: <20260420124032.GO2577880@ziepe.ca> References: <20260420123221.20801-1-epetron@amazon.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260420123221.20801-1-epetron@amazon.de> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260420_054039_426935_93BDAE8A X-CRM114-Status: GOOD ( 11.92 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Apr 20, 2026 at 12:32:01PM +0000, Evangelos Petrongonas wrote: > When the hardware advertises both Stage 1 and Stage 2 translation, the > driver prefers Stage 1 for DMA domain allocation and only falls back to > Stage 2 if Stage 1 is not supported. > > Some configurations may want to force Stage 2 translation even when the > hardware supports Stage 1. Why? You really need to explain why for a patch like this. If there really is some HW issue I think it is more appropriate to get an IORT flag or IDR detection that the HW has a problem. Jason