Messages in this thread | | | Date | Mon, 19 May 2014 09:11:05 +0200 | From | Sascha Hauer <> | Subject | Re: [PATCH v3] pwm: i.MX: Avoid sample FIFO overflow for i.MX PWM version2 |
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On Fri, May 16, 2014 at 01:11:08PM +0800, Liu Ying wrote: > The i.MX PWM version2 is embedded in several i.MX SoCs, > such as i.MX27, i.MX51 and i.MX6SL. There are four 16bit > sample FIFOs in this IP, each of which determines the duty > period of a PWM waveform in one full cycle. The IP spec > mentions that we should not write a fourth sample because > the FIFOs will become full and trigger a FIFO write error > (FWE) which will prevent the PWM from starting once it is > enabled. In order to avoid any sample FIFO overflow issue, > this patch clears all sample FIFOs or waits for a rollover > event to consume a FIFO slot when necessary. In this way, > only the first FIFO slot will be loaded at most. > > Note that the PWM controller will not generate any rollover > event if the duty period is zero. This makes the logic a > bit complicated to determine if we clear the sample FIFOs > or wait for a rollover event. > > The FIFO overflow issue can be reproduced by the following > commands on the i.MX6SL EVK platform, assuming we use PWM2 > for the debug LED which is driven by the pin HSIC_STROBE > and the maximal brightness is 255. > echo 0 > /sys/class/leds/user/brightness > echo 0 > /sys/class/leds/user/brightness > echo 0 > /sys/class/leds/user/brightness > echo 0 > /sys/class/leds/user/brightness > echo 255 > /sys/class/leds/user/brightness > Here, FWE happens(PWMSR register reads 0x58) and the LED > can not be lighten.
I find this overly complicated. It adds 89 lines to a 300 lines driver for a single workaround. Wouldn't it be sufficient to add a delay of period_ns in imx_pwm_config_v2 when the FIFO is full?
Sascha
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