From:   Nylon Chen <nylon.chen@sifive.com>
To:     aou@eecs.berkeley.edu, conor@kernel.org,
        emil.renner.berthing@canonical.com, geert+renesas@glider.be,
        heiko@sntech.de, krzysztof.kozlowski+dt@linaro.org,
        palmer@dabbelt.com, paul.walmsley@sifive.com, robh+dt@kernel.org,
        thierry.reding@gmail.com, u.kleine-koenig@pengutronix.de,
        devicetree@vger.kernel.org, linux-pwm@vger.kernel.org,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Cc:     nylon.chen@sifive.com, nylon7717@gmail.com, zong.li@sifive.com,
        greentime.hu@sifive.com, vincent.chen@sifive.com
Subject: [PATCH v2 2/2] pwm: sifive: change the PWM controlled LED algorithm
Date:   Mon, 30 Jan 2023 17:32:29 +0800
Message-Id: <20230130093229.27489-3-nylon.chen@sifive.com>
In-Reply-To: <20230130093229.27489-1-nylon.chen@sifive.com>
References: <20230130093229.27489-1-nylon.chen@sifive.com>
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The `frac` variable represents the pulse inactive time, and the result of
this algorithm is the pulse active time. Therefore, we must reverse the
result.

The reference is SiFive FU740-C000 Manual[0].

[0]: https://sifive.cdn.prismic.io/sifive/1a82e600-1f93-4f41-b2d8-86ed8b16acba_fu740-c000-manual-v1p6.pdf

Signed-off-by: Nylon Chen <nylon.chen@sifive.com>
---
 drivers/pwm/pwm-sifive.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/pwm/pwm-sifive.c b/drivers/pwm/pwm-sifive.c
index 62b6acc6373d..a5eda165d071 100644
--- a/drivers/pwm/pwm-sifive.c
+++ b/drivers/pwm/pwm-sifive.c
@@ -158,6 +158,7 @@ static int pwm_sifive_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 	frac = DIV64_U64_ROUND_CLOSEST(num, state->period);
 	/* The hardware cannot generate a 100% duty cycle */
 	frac = min(frac, (1U << PWM_SIFIVE_CMPWIDTH) - 1);
+	frac = (1U << PWM_SIFIVE_CMPWIDTH) - 1 - frac;
 
 	mutex_lock(&ddata->lock);
 	if (state->period != ddata->approx_period) {
-- 
2.36.1