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diff --git a/Documentation/nvme/feature-and-quirk-policy.rst b/Documentation/nvme/feature-and-quirk-policy.rst new file mode 100644 index 000000000000..c01d836d8e41 --- /dev/null +++ b/Documentation/nvme/feature-and-quirk-policy.rst @@ -0,0 +1,77 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================================= +Linux NVMe feature and and quirk policy +======================================= + +This file explains the policy used to decide what is supported by the +Linux NVMe driver and what is not. + + +Introduction +============ + +NVM Express is an open collection of standards and information. + +The Linux NVMe host driver in drivers/nvme/host/ supports devices +implementing the NVM Express (NVMe) family of specifications, which +currently consists of a number of documents: + + - the NVMe Base specification + - various Command Set specifications (e.g. NVM Command Set) + - various Transport specifications (e.g. PCIe, Fibre Channel, RDMA, TCP) + - the NVMe Management Interface specification + +See https://nvmexpress.org/developers/ for the NVMe specifications. + + +Supported features +================== + +NVMe is a large suite of specifications, and contains features that are only +useful or suitable for specific use-cases. It is important to note that Linux +does not aim to implement every feature in the specification. Every additional +feature implemented introduces more code, more maintenance and potentially more +bugs. Hence there is an inherent tradeoff between functionality and +maintainability of the NVMe host driver. + +Any feature implemented in the Linux NVMe host driver must support the +following requirements: + + 1. The feature is specified in a release version of an official NVMe + specification, or in a ratified Technical Proposal (TP) that is + available on NVMe website. Or if it is not directly related to the + on-wire protocol, does not contradict any of the NVMe specifications. + 2. Does not conflict with the Linux architecture, nor the design of the + NVMe host driver. + 3. Has a clear, indisputable value-proposition and a wide consensus across + the community. + +Vendor specific extensions are generally not supported in the NVMe host +driver. + +It is strongly recommended to work with the Linux NVMe and block layer +maintainers and get feedback on specification changes that are intended +to be used by the Linux NVMe host driver in order to avoid conflict at a +later stage. + + +Quirks +====== + +Sometimes implementations of open standards fail to correctly implement parts +of the standards. Linux uses identifier-based quirks to work around such +implementation bugs. The intent of quirks is to deal with widely available +hardware, usually consumer, which Linux users can't use without these quirks. +Typically these implementations are not or only superficially tested with Linux +by the hardware manufacturer. + +The Linux NVMe maintainers decide ad hoc whether to quirk implementations +based on the impact of the problem to Linux users and how it impacts +maintainability of the driver. In general quirks are a last resort, if no +firmware updates or other workarounds are available from the vendor. + +Quirks will not be added to the Linux kernel for hardware that isn't available +on the mass market. Hardware that fails qualification for enterprise Linux +distributions, ChromeOS, Android or other consumers of the Linux kernel +should be fixed before it is shipped instead of relying on Linux quirks. |