From: Sean Wang sean.wang@mediatek.com
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 --- drivers/pwm/pwm-mediatek.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-)
diff --git a/drivers/pwm/pwm-mediatek.c b/drivers/pwm/pwm-mediatek.c index 796baea..98b0a93 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);