mirror of
https://github.com/torvalds/linux.git
synced 2024-11-22 20:22:09 +00:00
8ca4fc323d
This adds a document about what specification features are supported by the Linux NVMe driver, and what qualifies for a quirk if an implementation has problems following the specification. Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: Keith Busch <kbusch@kernel.org> Signed-off-by: Sagi Grimberg <sagi@grimberg.me> Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Randy Dunlap <rdunlap@infradead.org> Acked-by: Jonathan Corbet <corbet@lwn.net>
78 lines
3.1 KiB
ReStructuredText
78 lines
3.1 KiB
ReStructuredText
.. 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.
|