From e5ca42458b6278b7d5866e08dae7c45349af2157 Mon Sep 17 00:00:00 2001 From: Dan O'Donovan Date: Wed, 1 Jun 2016 15:31:12 +0100 Subject: pwm: lpss: Fix base_unit calculation for PWM frequency The base_unit calculation applies an offset of 0x2 which adds significant error for lower frequencies and doesn't appear to be warranted - rounding the division result gives a correct value. Also, the upper limit check for base_unit is off-by-one; the upper nibble of base_unit is invalid if >=128 according to the Table 88 in the Z8000 Processor Series Datasheet Volume 1 (Rev. 2). Verified on UP Board (Cherry Trail) and Minnowboard Max (Bay Trail). Signed-off-by: Dan O'Donovan Acked-by: Mika Westerberg Signed-off-by: Thierry Reding --- drivers/pwm/pwm-lpss.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) (limited to 'drivers/pwm') diff --git a/drivers/pwm/pwm-lpss.c b/drivers/pwm/pwm-lpss.c index 295b963dbddb..98dc8b80b79d 100644 --- a/drivers/pwm/pwm-lpss.c +++ b/drivers/pwm/pwm-lpss.c @@ -27,7 +27,6 @@ #define PWM_SW_UPDATE BIT(30) #define PWM_BASE_UNIT_SHIFT 8 #define PWM_ON_TIME_DIV_MASK 0x000000ff -#define PWM_DIVISION_CORRECTION 0x2 /* Size of each PWM register space if multiple */ #define PWM_SIZE 0x400 @@ -101,17 +100,16 @@ static int pwm_lpss_config(struct pwm_chip *chip, struct pwm_device *pwm, /* * The equation is: - * base_unit = ((freq / c) * base_unit_range) + correction + * base_unit = round(base_unit_range * freq / c) */ base_unit_range = BIT(lpwm->info->base_unit_bits); - base_unit = freq * base_unit_range; + freq *= base_unit_range; c = lpwm->info->clk_rate; if (!c) return -EINVAL; - do_div(base_unit, c); - base_unit += PWM_DIVISION_CORRECTION; + base_unit = DIV_ROUND_CLOSEST_ULL(freq, c); if (duty_ns <= 0) duty_ns = 1; -- cgit v1.2.3