On Wed, Dec 21, 2022 at 06:45:32AM -0700, Jonathan Corbet wrote:
> Sorry, the argument is that the subsystem profiles there were created
> for the very purpose of documenting subsystem-specific patch policies
> like those found in your document. The hope is that, someday, people
> will be able to go to one place to learn what special hoops any given
> subsystem will make them jump through.
>
> This isn't something I'm going to dig in my heels on, though. But at a
> minimum, could you add an entry to
> Documentation/maintainer/maintainer-entry-profile.rst ?
What about the following? This moves the file to a new
Documentation/nvme/ directory and then links it form
Documentation/maintainer/maintainer-entry-profile.rst:
---
>From 3471fc6f0b584c4372d7c4c2b2b8e1b5aed970f0 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@xxxxxx>
Date: Mon, 12 Dec 2022 11:09:55 +0100
Subject: docs, nvme: add a feature and quirk policy document
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@xxxxxxxxx>
Signed-off-by: Keith Busch <kbusch@xxxxxxxxxx>
Signed-off-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
---
.../maintainer/maintainer-entry-profile.rst | 1 +
.../nvme/feature-and-quirk-policy.rst | 77 +++++++++++++++++++
MAINTAINERS | 1 +
3 files changed, 79 insertions(+)
create mode 100644 Documentation/nvme/feature-and-quirk-policy.rst
diff --git a/Documentation/maintainer/maintainer-entry-profile.rst b/Documentation/maintainer/maintainer-entry-profile.rst
index 93b2ae6c34a99b..cfd37f31077f6c 100644
--- a/Documentation/maintainer/maintainer-entry-profile.rst
+++ b/Documentation/maintainer/maintainer-entry-profile.rst
@@ -104,3 +104,4 @@ to do something different in the near future.
../riscv/patch-acceptance
../driver-api/media/maintainer-entry-profile
../driver-api/vfio-pci-device-specific-driver-acceptance
+ ../nvme/feature-and-quirk-policy
diff --git a/Documentation/nvme/feature-and-quirk-policy.rst b/Documentation/nvme/feature-and-quirk-policy.rst
new file mode 100644
index 00000000000000..c01d836d8e4151
--- /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.
diff --git a/MAINTAINERS b/MAINTAINERS
index bb77a3ed9d5423..d53b3a6cdc67d2 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14827,6 +14827,7 @@ L: linux-nvme@xxxxxxxxxxxxxxxxxxx
S: Supported
W: http://git.infradead.org/nvme.git
T: git://git.infradead.org/nvme.git
+F: Documentation/nvme/
F: drivers/nvme/host/
F: drivers/nvme/common/
F: include/linux/nvme*
--
2.35.1
