Commit 04c0a4e0 authored by Sean Wang's avatar Sean Wang Committed by Thierry Reding
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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: caf065f8 ("pwm: Add MediaTek PWM support")
Signed-off-by: default avatarSean Wang <sean.wang@mediatek.com>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent f3617876

drivers/pwm/pwm-mediatek.c

+12 −5
Original line number Diff line number Diff line
@@ -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);

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