Re: [PATCH v4] backlight: ktd253: Stabilize backlight

[Lee Jones <lee.jones@linaro.org>]

On Thu, 15 Jul 2021, Linus Walleij wrote:

> 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>
> ---
> ChangeLog v3->v4:
> - Collect Daniel's Reviewed-by.
> ChangeLog v2->v3:
> - Read my own patch and realized a bug: when we get a timeout
>   we bounce back to max period, but still count down the pwm
>   with one leading to an off-by-one error. Fix it by extending
>   some else clauses.
> ChangeLog v1->v2:
> - Alter the dimming code to check for how many ns the pulse
>   is low, and if it gets to ~100 us then redo from start.
>   This is to account for the advent that an IRQ arrives while
>   setting backlight and hits the low pulse making it way
>   too long.
> ---
>  drivers/video/backlight/ktd253-backlight.c | 75 ++++++++++++++++------
>  1 file changed, 55 insertions(+), 20 deletions(-)

Slight change of plan.

Looks like this fixes issues introduced in v5.9.  I tend to only
submit -fixes for issues added during the same merge cycle.

How loudly will you shout if I submit this for v5.15-rc1?

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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