diff options
Diffstat (limited to 'drivers/pwm/pwm-omap-dmtimer.c')
| -rw-r--r-- | drivers/pwm/pwm-omap-dmtimer.c | 74 |
1 files changed, 58 insertions, 16 deletions
diff --git a/drivers/pwm/pwm-omap-dmtimer.c b/drivers/pwm/pwm-omap-dmtimer.c index 826634ec0d5c..b7e6ecba7d5c 100644 --- a/drivers/pwm/pwm-omap-dmtimer.c +++ b/drivers/pwm/pwm-omap-dmtimer.c @@ -31,6 +31,7 @@ #include <linux/time.h> #define DM_TIMER_LOAD_MIN 0xfffffffe +#define DM_TIMER_MAX 0xffffffff struct pwm_omap_dmtimer_chip { struct pwm_chip chip; @@ -46,13 +47,9 @@ to_pwm_omap_dmtimer_chip(struct pwm_chip *chip) return container_of(chip, struct pwm_omap_dmtimer_chip, chip); } -static int pwm_omap_dmtimer_calc_value(unsigned long clk_rate, int ns) +static u32 pwm_omap_dmtimer_get_clock_cycles(unsigned long clk_rate, int ns) { - u64 c = (u64)clk_rate * ns; - - do_div(c, NSEC_PER_SEC); - - return DM_TIMER_LOAD_MIN - c; + return DIV_ROUND_CLOSEST_ULL((u64)clk_rate * ns, NSEC_PER_SEC); } static void pwm_omap_dmtimer_start(struct pwm_omap_dmtimer_chip *omap) @@ -99,12 +96,14 @@ static int pwm_omap_dmtimer_config(struct pwm_chip *chip, int duty_ns, int period_ns) { struct pwm_omap_dmtimer_chip *omap = to_pwm_omap_dmtimer_chip(chip); - int load_value, match_value; + u32 period_cycles, duty_cycles; + u32 load_value, match_value; struct clk *fclk; unsigned long clk_rate; bool timer_active; - dev_dbg(chip->dev, "duty cycle: %d, period %d\n", duty_ns, period_ns); + dev_dbg(chip->dev, "requested duty cycle: %d ns, period: %d ns\n", + duty_ns, period_ns); mutex_lock(&omap->mutex); if (duty_ns == pwm_get_duty_cycle(pwm) && @@ -117,15 +116,13 @@ static int pwm_omap_dmtimer_config(struct pwm_chip *chip, fclk = omap->pdata->get_fclk(omap->dm_timer); if (!fclk) { dev_err(chip->dev, "invalid pmtimer fclk\n"); - mutex_unlock(&omap->mutex); - return -EINVAL; + goto err_einval; } clk_rate = clk_get_rate(fclk); if (!clk_rate) { dev_err(chip->dev, "invalid pmtimer fclk rate\n"); - mutex_unlock(&omap->mutex); - return -EINVAL; + goto err_einval; } dev_dbg(chip->dev, "clk rate: %luHz\n", clk_rate); @@ -133,11 +130,51 @@ static int pwm_omap_dmtimer_config(struct pwm_chip *chip, /* * Calculate the appropriate load and match values based on the * specified period and duty cycle. The load value determines the - * cycle time and the match value determines the duty cycle. + * period time and the match value determines the duty time. + * + * The period lasts for (DM_TIMER_MAX-load_value+1) clock cycles. + * Similarly, the active time lasts (match_value-load_value+1) cycles. + * The non-active time is the remainder: (DM_TIMER_MAX-match_value) + * clock cycles. + * + * NOTE: It is required that: load_value <= match_value < DM_TIMER_MAX + * + * References: + * OMAP4430/60/70 TRM sections 22.2.4.10 and 22.2.4.11 + * AM335x Sitara TRM sections 20.1.3.5 and 20.1.3.6 */ - load_value = pwm_omap_dmtimer_calc_value(clk_rate, period_ns); - match_value = pwm_omap_dmtimer_calc_value(clk_rate, - period_ns - duty_ns); + period_cycles = pwm_omap_dmtimer_get_clock_cycles(clk_rate, period_ns); + duty_cycles = pwm_omap_dmtimer_get_clock_cycles(clk_rate, duty_ns); + + if (period_cycles < 2) { + dev_info(chip->dev, + "period %d ns too short for clock rate %lu Hz\n", + period_ns, clk_rate); + goto err_einval; + } + + if (duty_cycles < 1) { + dev_dbg(chip->dev, + "duty cycle %d ns is too short for clock rate %lu Hz\n", + duty_ns, clk_rate); + dev_dbg(chip->dev, "using minimum of 1 clock cycle\n"); + duty_cycles = 1; + } else if (duty_cycles >= period_cycles) { + dev_dbg(chip->dev, + "duty cycle %d ns is too long for period %d ns at clock rate %lu Hz\n", + duty_ns, period_ns, clk_rate); + dev_dbg(chip->dev, "using maximum of 1 clock cycle less than period\n"); + duty_cycles = period_cycles - 1; + } + + dev_dbg(chip->dev, "effective duty cycle: %lld ns, period: %lld ns\n", + DIV_ROUND_CLOSEST_ULL((u64)NSEC_PER_SEC * duty_cycles, + clk_rate), + DIV_ROUND_CLOSEST_ULL((u64)NSEC_PER_SEC * period_cycles, + clk_rate)); + + load_value = (DM_TIMER_MAX - period_cycles) + 1; + match_value = load_value + duty_cycles - 1; /* * We MUST stop the associated dual-mode timer before attempting to @@ -166,6 +203,11 @@ static int pwm_omap_dmtimer_config(struct pwm_chip *chip, mutex_unlock(&omap->mutex); return 0; + +err_einval: + mutex_unlock(&omap->mutex); + + return -EINVAL; } static int pwm_omap_dmtimer_set_polarity(struct pwm_chip *chip, |