[PATCH 0/2] leds: lp8864: Expose a backlight via led_bl helper

From: Alexander Sverdlin <[email protected]>

This series lets the TI LP8864/LP8866 LED driver expose a standard
backlight class device in addition to its LED class device, so it can
be consumed by display/panel stacks that expect a backlight.

This is a replacement for the earlier series "Convert LP8864 LED driver
to backlight class" [1], which took a much more invasive route: it moved
the driver from drivers/leds/ to drivers/video/backlight/ and added
backlight class registration on top.

Feedback on that approach was that a working LED driver should not be
relocated and re-typed just to gain a backlight interface.

The new approach keeps the LP8864 a plain LED driver and instead teaches
the existing generic led-backlight code to register a backlight on behalf
of a self-contained LED provider:

 * Patch 1 factors the backlight registration out of led_bl's probe path
   into a shared helper and exports devm_led_backlight_register(). This
   registers a backlight class device driven by a single LED, without a
   device-tree node, bound to the caller's device lifetime. The registration
   is now fully devres-managed, so the explicit .remove callback goes away.
   The exported symbol is a no-op when led-backlight support is not
   reachable (IS_REACHABLE(CONFIG_BACKLIGHT_LED)), so callers need no
   Kconfig plumbing and are not force-selected to build led_bl.

 * Patch 2 calls that helper from the LP8864 driver, spawning a backlight
   tied to the I2C device lifetime.

Compared to [1] this means:

 * The driver stays in drivers/leds/ and remains an ordinary LED driver.
 * The generic led_bl helper becomes reusable by other self-contained LED
   providers.

The motivating use case is unchanged: an LP8864 on a hot-pluggable segment
of an I2C bus. The generic led-backlight platform driver cannot react to a
dynamically (dis)appearing I2C device; letting the I2C driver register the
backlight directly makes it a self-contained, hot-plug-safe driver.

[1] https://lore.kernel.org/all/[email protected]/

Alexander Sverdlin (2):
  backlight: led_bl: Add devm_led_backlight_register() helper
  leds: lp8864: Register a backlight device

 drivers/leds/leds-lp8864.c       |   5 +-
 drivers/video/backlight/led_bl.c | 130 ++++++++++++++++++++-----------
 include/linux/led_bl.h           |  20 +++++
 3 files changed, 109 insertions(+), 46 deletions(-)
 create mode 100644 include/linux/led_bl.h

-- 
2.55.0