Hi, 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 <[email protected]> > Cc: Shawn Guo <[email protected]> > Cc: [email protected] > Cc: [email protected] > Signed-off-by: Liu Ying <[email protected]> > --- > drivers/pwm/pwm-imx.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/pwm/pwm-imx.c b/drivers/pwm/pwm-imx.c > index cc47733..efdce53 100644 > --- a/drivers/pwm/pwm-imx.c > +++ b/drivers/pwm/pwm-imx.c > @@ -38,6 +38,7 @@ > #define MX3_PWMCR_DBGEN (1 << 22) > #define MX3_PWMCR_CLKSRC_IPG_HIGH (2 << 16) > #define MX3_PWMCR_CLKSRC_IPG (1 << 16) > +#define MX3_PWMCR_SWR (1 << 3) > #define MX3_PWMCR_EN (1 << 0) > > struct imx_chip { > @@ -107,6 +108,12 @@ static int imx_pwm_config_v2(struct pwm_chip *chip, > unsigned long period_cycles, duty_cycles, prescale; > u32 cr; > > + /* do software reset in case fifo overflows */ > + writel(MX3_PWMCR_SWR, imx->mmio_base + MX3_PWMCR); > + do { > + cr = readl(imx->mmio_base + MX3_PWMCR); > + } while (cr & MX3_PWMCR_SWR); > + > An endless loop polling a hardware bit is ALWAYS a bad idea!
Lothar Waßmann -- ___________________________________________________________ Ka-Ro electronics GmbH | Pascalstraße 22 | D - 52076 Aachen Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10 Geschäftsführer: Matthias Kaussen Handelsregistereintrag: Amtsgericht Aachen, HRB 4996 www.karo-electronics.de | [email protected] ___________________________________________________________ -- To unsubscribe from this list: send the line "unsubscribe linux-pwm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
