Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit e5ca4245 authored by Dan O'Donovan's avatar Dan O'Donovan Committed by Thierry Reding
Browse files

pwm: lpss: Fix base_unit calculation for PWM frequency 



The base_unit calculation applies an offset of 0x2 which adds
significant error for lower frequencies and doesn't appear to be
warranted - rounding the division result gives a correct value.

Also, the upper limit check for base_unit is off-by-one; the upper
nibble of base_unit is invalid if >=128 according to the Table 88
in the Z8000 Processor Series Datasheet Volume 1 (Rev. 2).

Verified on UP Board (Cherry Trail) and Minnowboard Max (Bay Trail).

Signed-off-by: default avatarDan O'Donovan <dan@emutex.com>
Acked-by: default avatarMika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent cc37655e

drivers/pwm/pwm-lpss.c

+3 −5
Original line number Diff line number Diff line
@@ -27,7 +27,6 @@ 
#define PWM_SW_UPDATE			BIT(30)

#define PWM_BASE_UNIT_SHIFT		8

#define PWM_ON_TIME_DIV_MASK		0x000000ff

#define PWM_DIVISION_CORRECTION		0x2



/* Size of each PWM register space if multiple */

#define PWM_SIZE			0x400
@@ -101,17 +100,16 @@ static int pwm_lpss_config(struct pwm_chip *chip, struct pwm_device *pwm, 


	/*

	 * The equation is:

	 * base_unit = ((freq / c) * base_unit_range) + correction

	 * base_unit = round(base_unit_range * freq / c)

	 */

	base_unit_range = BIT(lpwm->info->base_unit_bits);

	base_unit = freq * base_unit_range;

	freq *= base_unit_range;



	c = lpwm->info->clk_rate;

	if (!c)

		return -EINVAL;



	do_div(base_unit, c);

	base_unit += PWM_DIVISION_CORRECTION;

	base_unit = DIV_ROUND_CLOSEST_ULL(freq, c);



	if (duty_ns <= 0)

		duty_ns = 1;