Messages in this thread | | | Date | Mon, 25 Aug 2014 19:59:01 +0800 | From | Shawn Guo <> | Subject | Re: [PATCH v5 3/3] pwm: i.MX: Avoid sample FIFO overflow for i.MX PWM version2 |
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On Wed, May 28, 2014 at 06:50:13PM +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 is a 4-word(16bit) > sample FIFO in this IP. Each FIFO slot 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 FIFO will become full and triggers 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 FIFO by doing software reset > in the configuration hook when the controller is disabled > or waits for a full PWM cycle to get a relinquished FIFO > slot when the controller is enabled and the FIFO is fully > loaded. > > 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. > > Another way to reproduce the FIFO overflow issue is to run > this script: > while true; > do echo 255 > /sys/class/leds/user/brightness; > done > > Cc: Thierry Reding <thierry.reding@gmail.com> > Cc: Sascha Hauer <s.hauer@pengutronix.de> > Cc: Shawn Guo <shawn.guo@freescale.com> > Cc: Lothar Waßmann <LW@KARO-electronics.de> > Cc: linux-pwm@vger.kernel.org > Cc: linux-arm-kernel@lists.infradead.org > Signed-off-by: Liu Ying <Ying.Liu@freescale.com>
The whole series,
Acked-by: Shawn Guo <shawn.guo@freescale.com>
Thierry,
Can you pick them up if they look good to you?
Shawn -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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