pwm: omap-dmtimer: Do not disable PWM before changing period/duty_cycle

Only the Timer control register(TCLR) cannot be updated when the timer
is running. Registers like Counter register (TCRR), loader register
(TLDR) and match register (TMAR) can be updated while the counter is
running. Since TCLR is not updated in pwm_omap_dmtimer_config(), do not
stop the timer for period/duty_cycle update.

Tested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

diff --git a/drivers/pwm/pwm-omap-dmtimer.c b/drivers/pwm/pwm-omap-dmtimer.c
index 85b17b49980b9914eb385f8ae9b6025bec4b079f..c56e7256e923a5105f08584843abe895e7dd8ad2 100644 (file)
--- a/drivers/pwm/pwm-omap-dmtimer.c
+++ b/drivers/pwm/pwm-omap-dmtimer.c
@@ -19,6 +19,13 @@
  * Limitations:
  * - When PWM is stopped, timer counter gets stopped immediately. This
  *   doesn't allow the current PWM period to complete and stops abruptly.
+ * - When PWM is running and changing both duty cycle and period,
+ *   we cannot prevent in software that the output might produce
+ *   a period with mixed settings. Especially when period/duty_cyle
+ *   is updated while the pwm pin is high, current pwm period/duty_cycle
+ *   can get updated as below based on the current timer counter:
+ *     - period for current cycle =  current_period + new period
+ *     - duty_cycle for current period = current period + new duty_cycle.
  */
 
 #include <linux/clk.h>
@@ -111,7 +118,6 @@ static int pwm_omap_dmtimer_config(struct pwm_chip *chip,
        u32 load_value, match_value;
        struct clk *fclk;
        unsigned long clk_rate;
-       bool timer_active;
 
        dev_dbg(chip->dev, "requested duty cycle: %d ns, period: %d ns\n",
                duty_ns, period_ns);
@@ -187,25 +193,12 @@ static int pwm_omap_dmtimer_config(struct pwm_chip *chip,
        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
-        * write its registers, but calls to omap_dm_timer_start/stop must
-        * be balanced so check if timer is active before calling timer_stop.
-        */
-       timer_active = pm_runtime_active(&omap->dm_timer_pdev->dev);
-       if (timer_active)
-               omap->pdata->stop(omap->dm_timer);
-
        omap->pdata->set_load(omap->dm_timer, load_value);
        omap->pdata->set_match(omap->dm_timer, true, match_value);
 
        dev_dbg(chip->dev, "load value: %#08x (%d), match value: %#08x (%d)\n",
                load_value, load_value, match_value, match_value);
 
-       /* If config was called while timer was running it must be reenabled. */
-       if (timer_active)
-               pwm_omap_dmtimer_start(omap);
-
        mutex_unlock(&omap->mutex);
 
        return 0;