The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 04c0a4e00dc11fedc0b0a8593adcf0f4310505d4 Mon Sep 17 00:00:00 2001

From: Sean Wang sean.wang@mediatek.com Date: Fri, 2 Mar 2018 16:49:14 +0800 Subject: [PATCH] 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: caf065f8fd58 ("pwm: Add MediaTek PWM support") Signed-off-by: Sean Wang sean.wang@mediatek.com Signed-off-by: Thierry Reding thierry.reding@gmail.com

diff --git a/drivers/pwm/pwm-mediatek.c b/drivers/pwm/pwm-mediatek.c index 502c366c7d7c..328c124773b2 100644 --- a/drivers/pwm/pwm-mediatek.c +++ b/drivers/pwm/pwm-mediatek.c @@ -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);