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 -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
