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Tue, 14 Apr 2020 10:04:47 -0700 (PDT) Received: from localhost.localdomain ([2001:171b:226b:54a0:116c:c27a:3e7f:5eaf]) by smtp.gmail.com with ESMTPSA id x18sm19549147wrs.11.2020.04.14.10.04.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Apr 2020 10:04:47 -0700 (PDT) From: Jean-Philippe Brucker To: iommu@lists.linux-foundation.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pci@vger.kernel.org, linux-mm@kvack.org Cc: joro@8bytes.org, catalin.marinas@arm.com, will@kernel.org, robin.murphy@arm.com, kevin.tian@intel.com, baolu.lu@linux.intel.com, Jonathan.Cameron@huawei.com, jacob.jun.pan@linux.intel.com, christian.koenig@amd.com, zhangfei.gao@linaro.org, jgg@ziepe.ca, xuzaibo@huawei.com, Jean-Philippe Brucker , Rob Herring Subject: [PATCH v5 21/25] dt-bindings: document stall property for IOMMU masters Date: Tue, 14 Apr 2020 19:02:49 +0200 Message-Id: <20200414170252.714402-22-jean-philippe@linaro.org> X-Mailer: git-send-email 2.26.0 In-Reply-To: <20200414170252.714402-1-jean-philippe@linaro.org> References: <20200414170252.714402-1-jean-philippe@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On ARM systems, some platform devices behind an IOMMU may support stall, which is the ability to recover from page faults. Let the firmware tell u= s when a device supports stall. Reviewed-by: Rob Herring Signed-off-by: Jean-Philippe Brucker --- .../devicetree/bindings/iommu/iommu.txt | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/Documentation/devicetree/bindings/iommu/iommu.txt b/Document= ation/devicetree/bindings/iommu/iommu.txt index 3c36334e4f942..26ba9e530f138 100644 --- a/Documentation/devicetree/bindings/iommu/iommu.txt +++ b/Documentation/devicetree/bindings/iommu/iommu.txt @@ -92,6 +92,24 @@ Optional properties: tagging DMA transactions with an address space identifier. By default, this is 0, which means that the device only has one address space. =20 +- dma-can-stall: When present, the master can wait for a transaction to + complete for an indefinite amount of time. Upon translation fault some + IOMMUs, instead of aborting the translation immediately, may first + notify the driver and keep the transaction in flight. This allows the = OS + to inspect the fault and, for example, make physical pages resident + before updating the mappings and completing the transaction. Such IOMM= U + accepts a limited number of simultaneous stalled transactions before + having to either put back-pressure on the master, or abort new faultin= g + transactions. + + Firmware has to opt-in stalling, because most buses and masters don't + support it. In particular it isn't compatible with PCI, where + transactions have to complete before a time limit. More generally it + won't work in systems and masters that haven't been designed for + stalling. For example the OS, in order to handle a stalled transaction= , + may attempt to retrieve pages from secondary storage in a stalled + domain, leading to a deadlock. + =20 Notes: =3D=3D=3D=3D=3D=3D --=20 2.26.0