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pwm: mediatek: Improve precision in rate calculation 

Add a way that turning resolution from in nanosecond into in picosecond
to improve noticeably almost 4.5% precision.

It's necessary to hold the new resolution with type u64 and thus related
operations on u64 are applied instead in those rate calculations.

And the patch has a dependency on [1].

[1] http://lists.infradead.org/pipermail/linux-mediatek/2018-March/012225.html

Cc: stable@vger.kernel.org
Fixes: caf065f8fd ("pwm: Add MediaTek PWM support")
Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
This commit is contained in:
Sean Wang 2018-03-02 16:49:14 +08:00 committed by Thierry Reding
parent f361787636
commit 04c0a4e00d
1 changed files with 12 additions and 5 deletions
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17
drivers/pwm/pwm-mediatek.c
View File

@ -135,19 +135,25 @@ static int mtk_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
{
struct mtk_pwm_chip *pc = to_mtk_pwm_chip(chip);
struct clk *clk = pc->clks[MTK_CLK_PWM1 + pwm->hwpwm];
u32 resolution, clkdiv = 0, reg_width = PWMDWIDTH,
u32 clkdiv = 0, cnt_period, cnt_duty, reg_width = PWMDWIDTH,
reg_thres = PWMTHRES;
u64 resolution;
int ret;
ret = mtk_pwm_clk_enable(chip, pwm);
if (ret < 0)
return ret;
resolution = NSEC_PER_SEC / clk_get_rate(clk);
/* Using resolution in picosecond gets accuracy higher */
resolution = (u64)NSEC_PER_SEC * 1000;
do_div(resolution, clk_get_rate(clk));
while (period_ns / resolution > 8191) {
cnt_period = DIV_ROUND_CLOSEST_ULL((u64)period_ns * 1000, resolution);
while (cnt_period > 8191) {
resolution *= 2;
clkdiv++;
cnt_period = DIV_ROUND_CLOSEST_ULL((u64)period_ns * 1000,
resolution);
}
if (clkdiv > PWM_CLK_DIV_MAX) {
@ -165,9 +171,10 @@ static int mtk_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
reg_thres = PWM45THRES_FIXUP;
}
cnt_duty = DIV_ROUND_CLOSEST_ULL((u64)duty_ns * 1000, resolution);
mtk_pwm_writel(pc, pwm->hwpwm, PWMCON, BIT(15) | clkdiv);
mtk_pwm_writel(pc, pwm->hwpwm, reg_width, period_ns / resolution);
mtk_pwm_writel(pc, pwm->hwpwm, reg_thres, duty_ns / resolution);
mtk_pwm_writel(pc, pwm->hwpwm, reg_width, cnt_period);
mtk_pwm_writel(pc, pwm->hwpwm, reg_thres, cnt_duty);
mtk_pwm_clk_disable(chip, pwm);