Pull backlight updates from Lee Jones:
 "Core Frameworks
   - Obtain scale type through sysfs

  New Functionality:
   - Provide Device Tree functionality in rave-sp-backlight
   - Calculate if scale type is (non-)linear in pwm_bl

  Fix-ups:
   - Simplify code in lm3630a_bl
   - Trivial rename/whitespace/typo fixes in lms283gf05
   - Remove superfluous NULL check in tosa_lcd
   - Fix power state initialisation in gpio_backlight
   - List supported file in MAINTAINERS

  Bug Fixes:
   - Kconfig - default to not building unless requested in
     {LED,BACKLIGHT}_CLASS_DEVICE"

* tag 'backlight-next-5.4' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/backlight:
  backlight: pwm_bl: Set scale type for brightness curves specified in the DT
  backlight: pwm_bl: Set scale type for CIE 1931 curves
  backlight: Expose brightness curve type through sysfs
  MAINTAINERS: Add entry for stable backlight sysfs ABI documentation
  backlight: gpio-backlight: Correct initial power state handling
  video: backlight: tosa_lcd: drop check because i2c_unregister_device() is NULL safe
  video: backlight: Drop default m for {LCD,BACKLIGHT_CLASS_DEVICE}
  backlight: lms283gf05: Fix a typo in the description passed to 'devm_gpio_request_one()'
  backlight: lm3630a: Switch to use fwnode_property_count_uXX()
  backlight: rave-sp: Leave initial state and register with correct device

Check if a brightness curve specified in the device tree is linear or
not and set the corresponding property accordingly. This makes the
scale type available to userspace via the 'scale' sysfs attribute.

To determine if a curve is linear it is compared to a interpolated linear
curve between min and max brightness. The curve is considered linear if
no value deviates more than +/-5% of ${brightness_range} from their
interpolated value.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

For backlight curves calculated with the CIE 1931 algorithm set
the brightness scale type to non-linear. This makes the scale type
available to userspace via the 'scale' sysfs attribute.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Tested-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Backlight brightness curves can have different shapes. The two main
types are linear and non-linear curves. The human eye doesn't
perceive linearly increasing/decreasing brightness as linear (see
also 88ba95bedb79 "backlight: pwm_bl: Compute brightness of LED
linearly to human eye"), hence many backlights use non-linear (often
logarithmic) brightness curves. The type of curve currently is opaque
to userspace, so userspace often uses more or less reliable heuristics
(like the number of brightness levels) to decide whether to treat a
backlight device as linear or non-linear.

Export the type of the brightness curve via the new sysfs attribute
'scale'. The value of the attribute can be 'linear', 'non-linear' or
'unknown'. For devices that don't provide information about the scale
of their brightness curve the value of the 'scale' attribute is 'unknown'.

Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

The default-on property - or the def_value via legacy pdata) should be
handled as:
if it is 1, the backlight must be enabled (kept enabled)
if it is 0, the backlight must be disabled (kept disabled)

This only works for the case when default-on is set. If it is not set then
the brightness of the backlight is set to 0. Now if the backlight is
enabled by external driver (graphics) the backlight will stay disabled since
the brightness is configured as 0. The backlight will not turn on.

In order to minimize screen flickering during device boot:

The initial brightness should be set to 1.

If booted in non DT mode or no phandle link to the backlight node:
follow the def_value/default-on to select UNBLANK or POWERDOWN

If in DT boot we have phandle link then leave the GPIO in a state which the
bootloader left it and let the user of the backlight to configure it
further.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

No need to check the argument of i2c_unregister_device() because the
function itself does it.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

When running "make oldconfig" on a .config where
CONFIG_BACKLIGHT_LCD_SUPPORT is not set, two new config options
("Lowlevel LCD controls" and "Lowlevel Backlight controls") appear, both
defaulting to "m".

Drop the "default m", as options should default to disabled, and because
several driver config options already select LCD_CLASS_DEVICE or
BACKLIGHT_CLASS_DEVICE when needed.

Fixes: 8c5dc8d9f19c7992 ("video: backlight: Remove useless BACKLIGHT_LCD_SUPPORT kernel symbol")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

The description passed to 'devm_gpio_request_one()' should be related to
LMS283GF05, not LMS285GF05.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Use use fwnode_property_count_uXX() directly, that makes code neater.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

This way the backlight can be referenced through its device node and
enabling/disabling can be managed through the panel driver.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>