From mboxrd@z Thu Jan 1 00:00:00 1970 From: shawn.guo@freescale.com (Shawn Guo) Date: Sun, 13 Apr 2014 15:46:45 +0800 Subject: [PATCH v2] pwm: i.MX: Avoid sample fifo overflow for i.MX pwm version2 In-Reply-To: <1397121829-19331-1-git-send-email-Ying.Liu@freescale.com> References: <1397121829-19331-1-git-send-email-Ying.Liu@freescale.com> Message-ID: <20140413074643.GD24180@dragon> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Apr 10, 2014 at 05:23:49PM +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 fifo > 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 > does software reset to clear all the sample fifos in the > very beginning of the pwm configuration function. > > 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. > > Cc: Sascha Hauer > Cc: Shawn Guo Acked-by: Shawn Guo > Cc: Lothar Wa?mann > Cc: linux-pwm at vger.kernel.org > Cc: linux-arm-kernel at lists.infradead.org > Signed-off-by: Liu Ying