Re: [PATCH net-next v16 6/6] net: dsa: mxl862xx: document devlink flash and info support

Re: [PATCH net-next v16 6/6] net: dsa: mxl862xx: document devlink flash and info support

[netdev-bot+sashiko]

Thank you for your contribution! Sashiko AI review found 1 potential
issue(s) to consider:

Critical: 0 · High: 0 · Medium: 1 · Low: 0

- [Medium] The new user-facing document and the in-tree driver artifacts
  disagree on the remedy for a failed rescue recovery.

--

net: dsa: mxl862xx: document devlink flash and info support

This adds Documentation/networking/devlink/mxl862xx.rst describing the
devlink info versions and the flash update flow of the mxl862xx driver,
including the MCUboot rescue mode recovery, links it from the devlink
index and adds it to the driver's MAINTAINERS entry.

> diff --git a/Documentation/networking/devlink/mxl862xx.rst b/Documentation/networking/devlink/mxl862xx.rst
> new file mode 100644
> index 0000000000000..793f3521f505f
> --- /dev/null
> +++ b/Documentation/networking/devlink/mxl862xx.rst
> @@ -0,0 +1,91 @@

[ ... ]

> +Flash Update
> +============

[ ... ]

> +If the driver gives up on the recovery, ``devlink dev flash`` returns
> +``-EIO`` and says so in its extack message. The drain runs once and is
> +never resumed, so a failed MDIO transaction ends it as well. A loader
> +that stops answering the drain needs a power cycle; a completed drain
> +whose reprobe could not be scheduled, and a drain a bus error cut
> +short, need only a driver rebind. The driver re-examines the switch
> +when it binds and at no other time, so a power cycle on a board where
> +the switch can be cycled on its own still has to be followed by an
> +unbind and rebind for the recovered switch to be recognised.

[Severity: Medium]

This new text says two of the three rescue_failed causes need only a
driver rebind, but the in-tree kernel-doc and the log message say a power
cycle is needed in all cases.  Which of the three is right?

The kernel-doc for the flag in struct mxl862xx_priv (mxl862xx.h) makes no
distinction:

 * @rescue_failed:      (rescue_mode) the self-heal gave up or cannot run; the
 *                      loader needs a power cycle and no flash can be accepted

and mxl862xx_setup_rescue() in mxl862xx.c prints the same advice for every
cause:

	if (priv->rescue_failed) {
		dev_warn(ds->dev,
			 "switch in MCUboot with an unfinishable download, power cycle it\n");
		return;
	}

mxl862xx_rescue_heal_work_fn() in mxl862xx-fw.c sets the flag both for any
drain error, which includes a plain SMDIO/bus write failure:

		dev_err(dev, "flash: download recovery failed: %pe\n",
			ERR_PTR(ret));
		WRITE_ONCE(priv->rescue_failed, true);

and after a fully successful drain when only the reprobe hand-off failed:

	if (device_schedule_reprobe(dev, MXL862XX_FW_REPROBE_DELAY_MS))
		WRITE_ONCE(priv->rescue_failed, true);

Since rescue_failed is a plain bool in the per-binding priv, an unbind and
rebind starts from false and re-runs mxl862xx_rescue_mode_detect(), which
matches what the .rst says for those two cases.  Only the unfinishable
opening handshake path in mxl862xx_rescue_mode_detect() looks like it
genuinely needs a power cycle.

Should the kernel-doc comment and the dev_warn() text be narrowed the same
way, so an operator reading dmesg is not sent to power cycle (possibly
physically reset) a switch that a rebind would recover?

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/cover.1789477568.git.daniel%40makrotopia.org

[PATCH net-next v16 6/6] net: dsa: mxl862xx: document devlink flash and info support

[Daniel Golle]

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.

Assisted-by: LLM
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
v16:
 - document that a reboot waits for a running flash and that one
   requested afterwards is refused, and that a bus error ends the
   download recovery for good
 - title-case the "Flash Update" heading, as the other devlink driver
   documents do
 - say that the ports come back down from a flash, that a reprobe which
   cannot be scheduled needs a rebind, and which of the two recovery
   failures needs a power cycle and which a rebind (found by Sashiko AI
   review)

v15:
 - asic.rev is read from the CHIP ID registers as well, not from one
   register word shared with asic.id (found by Sashiko AI review)
 - -EIO says the driver gave up on the recovery, which may need a driver
   rebind rather than a power cycle, and an interrupted opening
   handshake is reported the same way (found by Sashiko AI review)

v14: no changes

v13: no changes

v12: no changes

v11: no changes

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 | 91 +++++++++++++++++++
 MAINTAINERS                                   |  1 +
 3 files changed, 93 insertions(+)
 create mode 100644 Documentation/networking/devlink/mxl862xx.rst

diff --git a/Documentation/networking/devlink/index.rst b/Documentation/networking/devlink/index.rst
index d4a83fdcff7f..145cb8a4becf 100644
--- a/Documentation/networking/devlink/index.rst
+++ b/Documentation/networking/devlink/index.rst
@@ -95,6 +95,7 @@ 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..793f3521f505
--- /dev/null
+++ b/Documentation/networking/devlink/mxl862xx.rst
@@ -0,0 +1,91 @@
+.. 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 CHIP ID registers as well. Both
+       values are published behind the same check, 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; they
+come back registered but down, so userspace brings them up again. A
+complete flash and reprobe cycle takes about one minute. In the rare
+case that the reprobe cannot be scheduled at all, ``devlink dev
+flash`` reports that error and the driver stays bound to a switch it
+no longer tracks until it is unbound and rebound. A reboot started
+while an update is running waits for the transfer to finish, and an
+update requested after the system has begun shutting down is refused
+with ``-ENODEV``.
+
+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 driver gives up on the recovery, ``devlink dev flash`` returns
+``-EIO`` and says so in its extack message. The drain runs once and is
+never resumed, so a failed MDIO transaction ends it as well. A loader
+that stops answering the drain needs a power cycle; a completed drain
+whose reprobe could not be scheduled, and a drain a bus error cut
+short, need only a driver rebind. The driver re-examines the switch
+when it binds and at no other time, so a power cycle on a board where
+the switch can be cycled on its own still has to be followed by an
+unbind and rebind for the recovered switch to be recognised.
+
+A download interrupted during its opening handshake, before the image
+header reached the loader, is reported the same way. The loader waits
+for a header that no later session can supply, so that state needs a
+power cycle.
diff --git a/MAINTAINERS b/MAINTAINERS
index 0e04d92d1b09..43137dee4331 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -16248,6 +16248,7 @@ 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