Messages in this thread | | | Date | Tue, 28 Apr 2015 00:14:33 +0300 | From | Stas Sergeev <> | Subject | Re: [PATCH v2 0/3] leds: blink resolution improvements |
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Hi.
27.04.2015 23:54, Pavel Machek пишет: > Hi! > >> The following patches improve the precision of led >> timer trigger and add the delay unit control. >> That allows to make PWM brightness control with timer >> trigger. > Are you sure that is good idea? Doing LED pwm with main cpu is quite harsh... Do you remember the pc-speaker driver? :) In fact I tried the maximal possible freq on armada-xp board (it doesn't go above approx 100KHz, perhaps this all the HW timers can do on that board) and I haven't measured any noticeable CPU load with htop.
> We already have "brightness" for... well... brightness level. > > Would it make sense to have an option (Kconfig?) to do PWM using timer on hardware > that does not do hardware PWM? I think it would make sense, but not for the "timer" trigger. Maybe for "none" trigger, or inventing another trigger called "pwm". For the timer trigger I would pretty much like my approach to stay. The reason is that the PWM I need to do, is not strictly a PWM - it needs the ON period in range of tens or hundreds of milliseconds, while the OFF period is in a couple of usecs (or vice-versa). No generic PWM driver can afford such distribution, so I'd like to have the "timer" trigger for the unusual things like that. As I said, your idea can still be implemented for "none" trigger or some new trigger, so its still all for good.
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