leds/pwm: don't call pwm_disable when setting brightness
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Cover letter [PATCH 0/2] leds/pwm: don't call pwm_disable when setting brightness
Quoted 11 lines · Uwe Kleine-K?nig
[Cc: += akpm]
Quoted 3 lines · Uwe Kleine-K?nig
on arm/i.MX28 the leds connected to a pwm are still broken and it's more than three years ago that I came up with these patches. I still consider them to do the right thing and they fix a real bug.
I'm really frustrated here. I want to fix a real bug, made several suggestions (with patches) how to fix it and still have to include my local patches in each project that uses leds on i.MX28's pwm output.
Thierry, how can we get this resolved?
We have a couple of other drivers already solving similar issues. Look for example at the pwm-bcm-kona driver. It explicitly sets the duty cycle to 0 on ->disable() and then waits for some time before actually disabling the clock (specifically to avoid a similar than you seem to have on i.MX). See also the notes near the top of the driver source file.
Another example is pwm-samsung. It also has code specifically aimed at making sure the signal doesn't unexpectedly stay high after calling pwm_disable(). See also the commit message of:
6da89312a39b pwm: samsung: Fix output race on disabling
Both of these examples sound very similar to what you're describing, so I think it'd be best to follow these examples and fix the i.MX driver to behave as expected.
Irrespective of the behaviour of current drivers, the assumptions are already codified in the user drivers and they all assume that calling pwm_disable() means the PWM is off.
Thierry
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