1 .. SPDX-License-Identifier: GPL-2.0 2 3 ======================================= 4 Linux NVMe feature and and quirk policy 5 ======================================= 6 7 This file explains the policy used to decide what is supported by the 8 Linux NVMe driver and what is not. 9 10 11 Introduction 12 ============ 13 14 NVM Express is an open collection of standards and information. 15 16 The Linux NVMe host driver in drivers/nvme/host/ supports devices 17 implementing the NVM Express (NVMe) family of specifications, which 18 currently consists of a number of documents: 19 20 - the NVMe Base specification 21 - various Command Set specifications (e.g. NVM Command Set) 22 - various Transport specifications (e.g. PCIe, Fibre Channel, RDMA, TCP) 23 - the NVMe Management Interface specification 24 25 See https://nvmexpress.org/developers/ for the NVMe specifications. 26 27 28 Supported features 29 ================== 30 31 NVMe is a large suite of specifications, and contains features that are only 32 useful or suitable for specific use-cases. It is important to note that Linux 33 does not aim to implement every feature in the specification. Every additional 34 feature implemented introduces more code, more maintenance and potentially more 35 bugs. Hence there is an inherent tradeoff between functionality and 36 maintainability of the NVMe host driver. 37 38 Any feature implemented in the Linux NVMe host driver must support the 39 following requirements: 40 41 1. The feature is specified in a release version of an official NVMe 42 specification, or in a ratified Technical Proposal (TP) that is 43 available on NVMe website. Or if it is not directly related to the 44 on-wire protocol, does not contradict any of the NVMe specifications. 45 2. Does not conflict with the Linux architecture, nor the design of the 46 NVMe host driver. 47 3. Has a clear, indisputable value-proposition and a wide consensus across 48 the community. 49 50 Vendor specific extensions are generally not supported in the NVMe host 51 driver. 52 53 It is strongly recommended to work with the Linux NVMe and block layer 54 maintainers and get feedback on specification changes that are intended 55 to be used by the Linux NVMe host driver in order to avoid conflict at a 56 later stage. 57 58 59 Quirks 60 ====== 61 62 Sometimes implementations of open standards fail to correctly implement parts 63 of the standards. Linux uses identifier-based quirks to work around such 64 implementation bugs. The intent of quirks is to deal with widely available 65 hardware, usually consumer, which Linux users can't use without these quirks. 66 Typically these implementations are not or only superficially tested with Linux 67 by the hardware manufacturer. 68 69 The Linux NVMe maintainers decide ad hoc whether to quirk implementations 70 based on the impact of the problem to Linux users and how it impacts 71 maintainability of the driver. In general quirks are a last resort, if no 72 firmware updates or other workarounds are available from the vendor. 73 74 Quirks will not be added to the Linux kernel for hardware that isn't available 75 on the mass market. Hardware that fails qualification for enterprise Linux 76 distributions, ChromeOS, Android or other consumers of the Linux kernel 77 should be fixed before it is shipped instead of relying on Linux quirks.
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