On Thu, 22 Jul 2021, Daniel Thompson wrote:

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.

Reported-by: Marek Vasut <marex@denx.de>
Signed-off-by: Daniel Thompson <redacted>
Cc: stable@vger.kernel.org
Acked-by: Marek Vasut <marex@denx.de>
Tested-by: Marek Vasut <marex@denx.de>
---
 drivers/video/backlight/pwm_bl.c | 54 +++++++++++++++++---------------
 1 file changed, 28 insertions(+), 26 deletions(-)

Applied, thanks.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
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