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);