4.5-stable review patch. If anyone has any objections, please let me know.
------------------
From: David Rivshin <drivshin@xxxxxxxxxxx>
commit f8caa792261c0edded20eba2b8fcc899a1b91819 upstream.
Fix the calculation of load_value and match_value. Currently they
are slightly too low, which produces a noticeably wrong PWM rate with
sufficiently short periods (i.e. when 1/period approaches clk_rate/2).
Example:
clk_rate=32768Hz, period=122070ns, duty_cycle=61035ns (8192Hz/50% PWM)
Correct values: load = 0xfffffffc, match = 0xfffffffd
Current values: load = 0xfffffffa, match = 0xfffffffc
effective PWM: period=183105ns, duty_cycle=91553ns (5461Hz/50% PWM)
Fixes: 6604c6556db9 ("pwm: Add PWM driver for OMAP using dual-mode timers")
Signed-off-by: David Rivshin <drivshin@xxxxxxxxxxx>
Acked-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>
Tested-by: Adam Ford <aford173@xxxxxxxxx>
Signed-off-by: Thierry Reding <thierry.reding@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/pwm/pwm-omap-dmtimer.c | 27 ++++++++++++++++++++-------
1 file changed, 20 insertions(+), 7 deletions(-)
--- 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 +47,13 @@ to_pwm_omap_dmtimer_chip(struct pwm_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 c;
}
static void pwm_omap_dmtimer_start(struct pwm_omap_dmtimer_chip *omap)
@@ -99,7 +100,8 @@ static int pwm_omap_dmtimer_config(struc
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;
@@ -133,11 +135,22 @@ static int pwm_omap_dmtimer_config(struc
/*
* 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.
+ *
+ * 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);
+
+ 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
--
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