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); + c = clk_get_rate(imx->clk_per); c = c * period_ns; do_div(c, 1000000000); -- 1.7.9.5 -- 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
