diff options
| -rw-r--r-- | drivers/pwm/pwm-berlin.c | 45 |
1 files changed, 25 insertions, 20 deletions
diff --git a/drivers/pwm/pwm-berlin.c b/drivers/pwm/pwm-berlin.c index 771859aca4be..7c8d6a168ceb 100644 --- a/drivers/pwm/pwm-berlin.c +++ b/drivers/pwm/pwm-berlin.c @@ -21,8 +21,18 @@ #define BERLIN_PWM_EN 0x0 #define BERLIN_PWM_ENABLE BIT(0) #define BERLIN_PWM_CONTROL 0x4 -#define BERLIN_PWM_PRESCALE_MASK 0x7 -#define BERLIN_PWM_PRESCALE_MAX 4096 +/* + * The prescaler claims to support 8 different moduli, configured using the + * low three bits of PWM_CONTROL. (Sequentially, they are 1, 4, 8, 16, 64, + * 256, 1024, and 4096.) However, the moduli from 4 to 1024 appear to be + * implemented by internally shifting TCNT left without adding additional + * bits. So, the max TCNT that actually works for a modulus of 4 is 0x3fff; + * for 8, 0x1fff; and so on. This means that those moduli are entirely + * useless, as we could just do the shift ourselves. The 4096 modulus is + * implemented with a real prescaler, so we do use that, but we treat it + * as a flag instead of pretending the modulus is actually configurable. + */ +#define BERLIN_PWM_PRESCALE_4096 0x7 #define BERLIN_PWM_INVERT_POLARITY BIT(3) #define BERLIN_PWM_DUTY 0x8 #define BERLIN_PWM_TCNT 0xc @@ -46,10 +56,6 @@ static inline struct berlin_pwm_chip *to_berlin_pwm_chip(struct pwm_chip *chip) return container_of(chip, struct berlin_pwm_chip, chip); } -static const u32 prescaler_table[] = { - 1, 4, 8, 16, 64, 256, 1024, 4096 -}; - static inline u32 berlin_pwm_readl(struct berlin_pwm_chip *chip, unsigned int channel, unsigned long offset) { @@ -86,33 +92,32 @@ static int berlin_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm_dev, int duty_ns, int period_ns) { struct berlin_pwm_chip *pwm = to_berlin_pwm_chip(chip); - unsigned int prescale; + bool prescale_4096 = false; u32 value, duty, period; - u64 cycles, tmp; + u64 cycles; cycles = clk_get_rate(pwm->clk); cycles *= period_ns; do_div(cycles, NSEC_PER_SEC); - for (prescale = 0; prescale < ARRAY_SIZE(prescaler_table); prescale++) { - tmp = cycles; - do_div(tmp, prescaler_table[prescale]); + if (cycles > BERLIN_PWM_MAX_TCNT) { + prescale_4096 = true; + cycles >>= 12; // Prescaled by 4096 - if (tmp <= BERLIN_PWM_MAX_TCNT) - break; + if (cycles > BERLIN_PWM_MAX_TCNT) + return -ERANGE; } - if (tmp > BERLIN_PWM_MAX_TCNT) - return -ERANGE; - - period = tmp; - cycles = tmp * duty_ns; + period = cycles; + cycles *= duty_ns; do_div(cycles, period_ns); duty = cycles; value = berlin_pwm_readl(pwm, pwm_dev->hwpwm, BERLIN_PWM_CONTROL); - value &= ~BERLIN_PWM_PRESCALE_MASK; - value |= prescale; + if (prescale_4096) + value |= BERLIN_PWM_PRESCALE_4096; + else + value &= ~BERLIN_PWM_PRESCALE_4096; berlin_pwm_writel(pwm, pwm_dev->hwpwm, value, BERLIN_PWM_CONTROL); berlin_pwm_writel(pwm, pwm_dev->hwpwm, duty, BERLIN_PWM_DUTY); |