[U-Boot] [PATCH 3/9 v2] Exynos: pwm: Fix two bugs in the exynos pwm configuration code
Akshay Saraswat
akshay.s at samsung.com
Thu Feb 28 11:59:18 CET 2013
First, the "div" value was being used incorrectly to compute the frequency of
the PWM timer. The value passed in is a constant which reflects the value
that would be found in a configuration register, 0 to 4. That should
correspond to a scaling factor of 1, 2, 4, 8, or 16, 1 << div, but div + 1 was
being used instead.
Second, the reset value of the timers were being calculated to give an overall
frequency, thrown out, and set to a maximum value. This was done so that PWM 4
could be used as the system clock by counting down from a high value, but it
was applied indiscriminantly. It should at most be applied only to PWM 4.
This change also takes the opportunity to tidy up the pwm_init function.
Test with command "sf probe 1:0; time sf read 40008000 0 1000".
Try with different numbers of bytes and see that sane values are obtained
Build and boot U-boot with this patch, backlight works properly.
Signed-off-by: Gabe Black <gabeblack at google.com>
Signed-off-by: Akshay Saraswat <akshay.s at samsung.com>
Acked-by: Simon Glass <sjg at chromium.org>
---
Changes since v1:
- Added "Acked-by: Simon Glass".
arch/arm/cpu/armv7/s5p-common/pwm.c | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)
diff --git a/arch/arm/cpu/armv7/s5p-common/pwm.c b/arch/arm/cpu/armv7/s5p-common/pwm.c
index 3147f59..02156d1 100644
--- a/arch/arm/cpu/armv7/s5p-common/pwm.c
+++ b/arch/arm/cpu/armv7/s5p-common/pwm.c
@@ -143,7 +143,7 @@ int pwm_init(int pwm_id, int div, int invert)
u32 val;
const struct s5p_timer *pwm =
(struct s5p_timer *)samsung_get_base_timer();
- unsigned long timer_rate_hz;
+ unsigned long ticks_per_period;
unsigned int offset, prescaler;
/*
@@ -167,20 +167,24 @@ int pwm_init(int pwm_id, int div, int invert)
val |= (div & 0xf) << MUX_DIV_SHIFT(pwm_id);
writel(val, &pwm->tcfg1);
- timer_rate_hz = get_pwm_clk() / ((prescaler + 1) *
- (div + 1));
+ if (pwm_id == 4) {
+ /*
+ * TODO(sjg): Use this as a countdown timer for now. We count
+ * down from the maximum value to 0, then reset.
+ */
+ ticks_per_period = -1UL;
+ } else {
+ const unsigned long pwm_hz = 1000;
+ unsigned long timer_rate_hz = get_pwm_clk() /
+ ((prescaler + 1) * (1 << div));
- timer_rate_hz = timer_rate_hz / CONFIG_SYS_HZ;
+ ticks_per_period = timer_rate_hz / pwm_hz;
+ }
/* set count value */
offset = pwm_id * 3;
- /*
- * TODO(sjg): Use this as a countdown timer for now. We count down
- * from the maximum value to 0, then reset.
- */
- timer_rate_hz = -1;
- writel(timer_rate_hz, &pwm->tcntb0 + offset);
+ writel(ticks_per_period, &pwm->tcntb0 + offset);
val = readl(&pwm->tcon) & ~(0xf << TCON_OFFSET(pwm_id));
if (invert && (pwm_id < 4))
--
1.8.0
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