[PATCH RFC v2 0/1] leds: asus-aura-scsi: Add ASUS Aura RGB LED driver for ROG NVMe enclosures

[Liang Haowen <nbg2974@gmail.com>]

Hello,

v2 of the LED driver for ASUS Aura RGB on ROG external NVMe
enclosures. It addresses all seven points from the review v1 received
(from the sashiko AI bot; there has been no human review on v1 yet).

Changes since v1:

- Teardown order: .detach() and the attach error path now unregister
  the LED class devices first, then cancel_work_sync(), then free.
  The v1 order (cancel first) left a window where a brightness write
  could requeue the work after cancel_work_sync() returned, so the
  work would run on freed memory.

- Request allocation: ene_write() now builds the request with
  scsi_alloc_request() instead of a raw blk_mq_alloc_request().
  scsi_initialize_rq() zeroes cmnd, initializes the rcu head, sense
  length and retries; skipping that left those fields uninitialized.
  An explicit timeout and RQF_QUIET are set, matching what
  scsi_execute_cmd() does.

- Serialization of the ENE sequence: brightness_set() now only caches
  the colour and marks the LED in a per-zone dirty bitmap; a single
  work item per zone runs one sequence (MODE, colour slots, APPLY,
  SAVE) for all pending LEDs. The v1 per-LED works could interleave
  their sequences between concurrent updates. As a side effect,
  multi-LED updates now batch into one APPLY/SAVE.

- Subject line: switched to the leds subsystem prefix and
  capitalization.

- The attach success log message is gone.

Two of the reported items did not hold up against the kernel this
driver is built against (7.2.2):

- kzalloc_obj() is not an undefined macro; it lives in
  include/linux/slab.h (since v6.17).

- blk_rq_map_kern() with four arguments is the current signature
  (rq, buf, len, gfp); drivers/scsi/scsi_lib.c calls it that way from
  scsi_execute_cmd().

Everything else is unchanged from v1: the hardware (ROG external NVMe
enclosures, e.g. ROG STRIX Arion, USB 0b05:1932, no HID, ENE LED
controller behind vendor SCSI commands on the disk's LUN, 4
independently addressable LEDs), the scsi_device_handler that does
not claim the sdev, the multicolor LED interface, and the
protocol handling. v2 was re-verified on hardware.

Known caveats, unchanged:

- the handler attaches manually until a notifier lands
  (echo asus_aura > /sys/block/sdX/device/dh_state);

- SAVE (0xaa) is issued with every colour update, which writes the
  enclosure flash each time; wear has not been characterized yet;

- the LEDs are registered with a NULL parent device, because
  parenting them to the sdev creates a reference cycle that blocks
  the sdev's final release on unplug.

Comments on the interface shape and on folding this into the shared
Aura work with Denis remain very welcome.

Signed-off-by: Liang Haowen <nbg2974@gmail.com>

Liang Haowen (1):
  leds: asus-aura-scsi: Add ASUS Aura RGB LED driver for ROG NVMe enclosures

 drivers/leds/leds-asus-aura-scsi.c | 332 +++++++++++++++++++++++++++++
 1 file changed, 332 insertions(+)

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2.55.0