[PATCH net-next v10 5/5] net: dsa: mxl862xx: document devlink flash and info support

[Daniel Golle <daniel@makrotopia.org>]

Describe the devlink info versions and the flash update behaviour,
including the MCUboot rescue mode recovery, in a dedicated file under
Documentation/networking/devlink/ and link it from the index. Add the
new file to the driver's MAINTAINERS entry.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
---
v10: document that a switch power cycled on its own needs the driver
     unbound and rebound before a failed recovery is re-examined
v9: no changes, picked up Andrew's v5 Reviewed-by
v8:
 - asic.id and asic.rev are omitted whenever the part number reads
   zero, not only in MCUboot rescue mode (found by Sashiko AI review)
 - drop the claim that "0.0.0" marks a switch that never ran firmware;
   rescue mode always reports it (found by Sashiko AI review)
 - document devlink dev flash as the signal that says whether a
   recovery is still running, including the -EIO it returns once the
   recovery has failed (found by Sashiko AI review)
v7: no changes
v6: no changes
v5: new patch, splitting the devlink documentation out of the flash
    update and rescue mode recovery patches so each keeps to code
    (Jakub Kicinski asked for the documentation)

 Documentation/networking/devlink/index.rst    |  1 +
 Documentation/networking/devlink/mxl862xx.rst | 74 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 3 files changed, 76 insertions(+)
 create mode 100644 Documentation/networking/devlink/mxl862xx.rst

diff --git a/Documentation/networking/devlink/index.rst b/Documentation/networking/devlink/index.rst
index 4745148fecf4..058999d0dc56 100644
--- a/Documentation/networking/devlink/index.rst
+++ b/Documentation/networking/devlink/index.rst
@@ -94,6 +94,7 @@ parameters, info versions, and other features it supports.
    mlx5
    mlxsw
    mv88e6xxx
+   mxl862xx
    netdevsim
    nfp
    octeontx2
diff --git a/Documentation/networking/devlink/mxl862xx.rst b/Documentation/networking/devlink/mxl862xx.rst
new file mode 100644
index 000000000000..5b24d8cb57bc
--- /dev/null
+++ b/Documentation/networking/devlink/mxl862xx.rst
@@ -0,0 +1,74 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+========================
+mxl862xx devlink support
+========================
+
+This document describes the devlink features implemented by the
+``mxl862xx`` device driver.
+
+Info versions
+=============
+
+The ``mxl862xx`` driver reports the following versions
+
+.. list-table:: devlink info versions implemented
+   :widths: 5 5 5 85
+
+   * - Name
+     - Type
+     - Example
+     - Description
+   * - ``asic.id``
+     - fixed
+     - 8628
+     - The chip part number read from the CHIP ID registers. Omitted
+       when the part number reads as zero, which happens for a switch
+       sitting in MCUboot rescue mode (the registers need a running
+       firmware), for an unfused part, and after a failed flash.
+   * - ``asic.rev``
+     - fixed
+     - 0
+     - The chip version read from the same register word, so it is
+       omitted whenever ``asic.id`` is.
+   * - ``fw``
+     - running, stored
+     - 1.0.70
+     - Version of the firmware running on the switch, reported as both
+       running and stored since the switch boots it from its own flash.
+       It is omitted while no firmware version is known: after a failed
+       flash, and in MCUboot rescue mode while an interrupted download
+       is still being recovered in the background. Once the loader is
+       ready to accept a new image the version appears as "0.0.0",
+       which no released firmware reports, so version-comparing tools
+       offer any available release as an upgrade. Use ``devlink dev
+       flash`` to tell a recovering switch from a ready one, see below;
+       a missing version on its own does not say why.
+
+Flash update
+============
+
+The ``mxl862xx`` driver implements support for ``devlink dev flash``.
+The signed firmware image is transferred to the switch over the same
+MDIO bus which is also used to manage the switch, then verified and
+installed by the MCUboot bootloader running on the switch. All ports
+of the switch are closed for the duration of the update and the driver
+reprobes the switch after it has rebooted into the new firmware. A
+complete flash and reprobe cycle takes about one minute.
+
+A switch stuck in MCUboot rescue mode, e.g. after an interrupted
+update, is registered without user ports. If the previous download was
+interrupted mid-transfer the loader is wedged; the driver drains it
+back to a clean ready state in the background, one byte at a time,
+which takes tens of minutes for a large image and is reported through
+the kernel log as it progresses. During that recovery ``devlink dev
+flash`` returns ``-EBUSY`` with an extack message saying so, and
+``devlink dev info`` reports no firmware version. Once the loader is
+ready the firmware version appears and flashing a firmware image
+through the regular update flow recovers the switch.
+
+If the recovery fails, the loader needs a power cycle: ``devlink dev
+flash`` then returns ``-EIO`` and says so in its extack message. The
+driver only re-examines the switch when it binds, so on a board where
+the switch can be power cycled on its own, unbind and rebind the driver
+afterwards to have the recovered switch recognised.
diff --git a/MAINTAINERS b/MAINTAINERS
index 03bfb79fca2a..8d9b1ea3faad 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -16107,6 +16107,7 @@ M:	Daniel Golle <daniel@makrotopia.org>
 L:	netdev@vger.kernel.org
 S:	Maintained
 F:	Documentation/devicetree/bindings/net/dsa/maxlinear,mxl862xx.yaml
+F:	Documentation/networking/devlink/mxl862xx.rst
 F:	drivers/net/dsa/mxl862xx/
 F:	net/dsa/tag_mxl862xx.c
 
-- 
2.55.0