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authorHans de Goede <hdegoede@redhat.com>2020-09-03 14:23:29 +0300
committerHans de Goede <hdegoede@redhat.com>2020-09-06 16:38:02 +0300
commita05af71f0dd3a31c4036f34e3e85fbcc56e80050 (patch)
treeb3b1bed0b3c5bd3ee3dc02ff97e0d8b506914317 /drivers/pwm
parent79e0899275e527ac187693528ba7a39a645e2832 (diff)
downloadlinux-a05af71f0dd3a31c4036f34e3e85fbcc56e80050.tar.xz
pwm: crc: Fix off-by-one error in the clock-divider calculations
The CRC PWM controller has a clock-divider which divides the clock with a value between 1-128. But as can seen from the PWM_DIV_CLK_xxx defines, this range maps to a register value of 0-127. So after calculating the clock-divider we must subtract 1 to get the register value, unless the requested frequency was so high that the calculation has already resulted in a (rounded) divider value of 0. Note that before this fix, setting a period of PWM_MAX_PERIOD_NS which corresponds to the max. divider value of 128 could have resulted in a bug where the code would use 128 as divider-register value which would have resulted in an actual divider value of 0 (and the enable bit being set). A rounding error stopped this bug from actually happen. This same rounding error means that after the subtraction of 1 it is impossible to set the divider to 128. Also bump PWM_MAX_PERIOD_NS by 1 ns to allow setting a divider of 128 (register-value 127). Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Acked-by: Thierry Reding <thierry.reding@gmail.com> Signed-off-by: Hans de Goede <hdegoede@redhat.com> Link: https://patchwork.freedesktop.org/patch/msgid/20200903112337.4113-10-hdegoede@redhat.com
Diffstat (limited to 'drivers/pwm')
-rw-r--r--drivers/pwm/pwm-crc.c17
1 files changed, 14 insertions, 3 deletions
diff --git a/drivers/pwm/pwm-crc.c b/drivers/pwm/pwm-crc.c
index c056eb9b858c..44ec7d5b63e1 100644
--- a/drivers/pwm/pwm-crc.c
+++ b/drivers/pwm/pwm-crc.c
@@ -22,7 +22,7 @@
#define PWM_MAX_LEVEL 0xFF
#define PWM_BASE_CLK_MHZ 6 /* 6 MHz */
-#define PWM_MAX_PERIOD_NS 5461333 /* 183 Hz */
+#define PWM_MAX_PERIOD_NS 5461334 /* 183 Hz */
/**
* struct crystalcove_pwm - Crystal Cove PWM controller
@@ -39,6 +39,18 @@ static inline struct crystalcove_pwm *to_crc_pwm(struct pwm_chip *pc)
return container_of(pc, struct crystalcove_pwm, chip);
}
+static int crc_pwm_calc_clk_div(int period_ns)
+{
+ int clk_div;
+
+ clk_div = PWM_BASE_CLK_MHZ * period_ns / (256 * NSEC_PER_USEC);
+ /* clk_div 1 - 128, maps to register values 0-127 */
+ if (clk_div > 0)
+ clk_div--;
+
+ return clk_div;
+}
+
static int crc_pwm_enable(struct pwm_chip *c, struct pwm_device *pwm)
{
struct crystalcove_pwm *crc_pwm = to_crc_pwm(c);
@@ -68,11 +80,10 @@ static int crc_pwm_config(struct pwm_chip *c, struct pwm_device *pwm,
}
if (pwm_get_period(pwm) != period_ns) {
- int clk_div;
+ int clk_div = crc_pwm_calc_clk_div(period_ns);
/* changing the clk divisor, need to disable fisrt */
crc_pwm_disable(c, pwm);
- clk_div = PWM_BASE_CLK_MHZ * period_ns / (256 * NSEC_PER_USEC);
regmap_write(crc_pwm->regmap, PWM0_CLK_DIV,
clk_div | PWM_OUTPUT_ENABLE);