Re: [v13 2/2] pwm: Add Aspeed ast2600 PWM support - Uwe Kleine-König

From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Billy Tsai <billy_tsai@aspeedtech.com>
Cc: jdelvare@suse.com, linux@roeck-us.net, robh+dt@kernel.org,
	joel@jms.id.au, andrew@aj.id.au, lee.jones@linaro.org,
	thierry.reding@gmail.com, p.zabel@pengutronix.de,
	linux-hwmon@vger.kernel.org, devicetree@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-aspeed@lists.ozlabs.org, linux-kernel@vger.kernel.org,
	linux-pwm@vger.kernel.org, BMC-SW@aspeedtech.com
Subject: Re: [v13 2/2] pwm: Add Aspeed ast2600 PWM support
Date: Mon, 29 Nov 2021 21:51:54 +0100	[thread overview]
Message-ID: <20211129205154.jtm4ehvvfo52toth@pengutronix.de> (raw)
In-Reply-To: <20211129064329.27006-3-billy_tsai@aspeedtech.com>

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Hello Billy,

just two minor thing left to criticise:

On Mon, Nov 29, 2021 at 02:43:29PM +0800, Billy Tsai wrote:
> +	if (clk_en && duty_pt) {
> +		dividend = (u64)NSEC_PER_SEC * (div_l + 1) * duty_pt
> +				 << div_h;
> +		state->duty_cycle = DIV_ROUND_UP_ULL(dividend, rate);
> +	} else
> +		state->duty_cycle = clk_en ? state->period : 0;

I wonder about checkpatch not criticising this construct. See
Documentation/process/coding-style.rst:

	Do not unnecessarily use braces where a single statement will
	do. [...] This does not apply if only one branch of a
	conditional statement is a single statement; in the latter case
	use braces in both branches

> [...]
> +static int aspeed_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			    const struct pwm_state *state)
> +{
> +	struct device *dev = chip->dev;
> +	struct aspeed_pwm_data *priv = aspeed_pwm_chip_to_data(chip);
> +	u32 hwpwm = pwm->hwpwm, duty_pt;
> +	unsigned long rate;
> +	u64 div_h, div_l, divisor, expect_period;
> +	bool clk_en;
> +
> +	expect_period = state->period;
> +	dev_dbg(dev, "expect period: %lldns, duty_cycle: %lldns", expect_period,
> +		state->duty_cycle);
> +
> +	rate = clk_get_rate(priv->clk);
> +	if (expect_period > div64_u64(ULLONG_MAX, (u64)rate))
> +		expect_period = div64_u64(ULLONG_MAX, (u64)rate);

If you write that as

	expect_period = min(div64_u64(ULLONG_MAX, (u64)rate), expect_period);

you make sure that the division is only calculated once.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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