Currently there are (at least) two problems in the way pwm_bl starts
managing the enable_gpio pin. Both occur when the backlight is initially
off and the driver finds the pin not already in output mode and, as a
result, unconditionally switches it to output-mode and asserts the signal.

Problem 1: This could cause the backlight to flicker since, at this stage
in driver initialisation, we have no idea what the PWM and regulator are
doing (an unconfigured PWM could easily "rest" at 100% duty cycle).

Problem 2: This will cause us not to correctly honour the
post_pwm_on_delay (which also risks flickers).

Fix this by moving the code to configure the GPIO output mode until after
we have examines the handover state. That allows us to initialize
enable_gpio to off if the backlight is currently off and on if the
backlight is on.

Cc: stable@vger.kernel.org
Reported-by: Marek Vasut <marex@denx.de>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Marek Vasut <marex@denx.de>
Tested-by: Marek Vasut <marex@denx.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Remove interrupt disablement during backlight setting. It is
way to dangerous and makes platforms instable by having it
miss vblank IRQs leading to the graphics derailing.

The code is using ndelay() which is not available on
platforms such as ARM and will result in 32 * udelay(1)
which is substantial.

Add some code to detect if an interrupt occurs during the
tight loop and in that case just redo it from the top.

Fixes: 5317f37e48b9 ("backlight: Add Kinetic KTD253 backlight driver")
Cc: Stephan Gerhold <stephan@gerhold.net>
Reported-by: newbyte@disroot.org
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

The practical upside here is that this only needs a single API call to
program the hardware which (depending on the underlaying hardware) can
be more effective and prevents glitches.

Up to now the return value of the pwm functions was ignored. Fix this
and propagate the error to the caller.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

According to <linux/backlight.h> .update_status() is supposed to
return 0 on success and a negative error code otherwise. Adapt
lm3630a_bank_a_update_status() and lm3630a_bank_b_update_status() to
actually do it.

While touching that also add the error code to the failure message.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Remove leading whitespaces, replace multi spaces with tabs, and fix help
text indentation.

Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Add a compatible for PMI8994 WLED. It uses the V4 of WLED IP.

Signed-off-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Adds support for Richtek RT4831 backlight.

Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

device_for_each_child_node() bumps a reference counting of a returned variable.
We have to balance it whenever we return to the caller.

Cc: Brian Masney <masneyb@onstation.org>
Cc: Dan Murphy <dmurphy@ti.com>
Fixes: 8fbce8efe15cd ("backlight: lm3630a: Add firmware node support")
Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Brian Masney <masneyb@onstation.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

With gcc-11, we get a warning about code that looks correct
but badly indented:

drivers/video/backlight/jornada720_bl.c: In function ‘jornada_bl_update_status’:
drivers/video/backlight/jornada720_bl.c:66:11: error: this ‘else’ clause does not guard... [-Werror=misleading-indentation]
   66 |         } else  /* turn on backlight */
      |           ^~~~

Change the formatting according to our normal conventions.

Fixes: 13a7b5dc0d17 ("backlight: Adds HP Jornada 700 series backlight driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

As per the current implementation, after FSC (Full Scale Current)
and brightness update the sync bits are set-then-cleared.
But, the FSC and brightness sync takes place when the sync bits are
set (e.g. on a rising edge). So the hardware team recommends a
clear-then-set approach in order to guarantee such a transition
regardless of the previous register state.

Signed-off-by: Kiran Gunda <kgunda@codeaurora.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>