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From: Guru Das Srinagesh <gurus@codeaurora.org>
To: linux-pwm@vger.kernel.org,
	"Thierry Reding" <thierry.reding@gmail.com>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Subbaraman Narayanamurthy <subbaram@codeaurora.org>,
	David Collins <collinsd@codeaurora.org>,
	linux-kernel@vger.kernel.org, Joe Perches <joe@perches.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Guenter Roeck <linux@roeck-us.net>,
	Daniel Thompson <daniel.thompson@linaro.org>,
	Dan Carpenter <dan.carpenter@oracle.com>,
	Guru Das Srinagesh <gurus@codeaurora.org>
Subject: [RESEND PATCH v14 06/11] pwm: imx27: Use 64-bit division macro and function
Date: Mon,  4 May 2020 11:50:12 -0700
Message-ID: <72e4dcdde37461ed7f9490a4742b65204787e687.1588616856.git.gurus@codeaurora.org> (raw)
In-Reply-To: <cover.1588616856.git.gurus@codeaurora.org>
In-Reply-To: <cover.1588616856.git.gurus@codeaurora.org>

Since the PWM framework is switching struct pwm_state.period's
datatype to u64, prepare for this transition by using
DIV_ROUND_UP_ULL to handle a 64-bit dividend, and div64_u64 to handle a
64-bit divisor.

Also handle a possible overflow in the calculation of period_cycles when
both clk_rate and period are large numbers. This logic was unit-tested
out by calculating period_cycles using both the existing logic and the
proposed one, and the results are as below.

----------------------------------------------------------------------------
 clk_rate            period           existing            proposed
----------------------------------------------------------------------------
1000000000   18446744073709551615    18446744072    18446744073000000000
                   (U64_MAX)
----------------------------------------------------------------------------
1000000000        4294967291         4294967291         4294967291
----------------------------------------------------------------------------

Overflow occurs in the first case with the existing logic, whereas the
proposed logic handles it better, sacrificing some precision in a best-effort
attempt to handle overflow. As for the second case where there are
more typical values of period, the proposed logic handles that correctly
too.

Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>
---
 drivers/pwm/pwm-imx27.c | 53 +++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 45 insertions(+), 8 deletions(-)

diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c
index a6e40d4..164cb65 100644
--- a/drivers/pwm/pwm-imx27.c
+++ b/drivers/pwm/pwm-imx27.c
@@ -203,7 +203,7 @@ static void pwm_imx27_wait_fifo_slot(struct pwm_chip *chip,
 	sr = readl(imx->mmio_base + MX3_PWMSR);
 	fifoav = FIELD_GET(MX3_PWMSR_FIFOAV, sr);
 	if (fifoav == MX3_PWMSR_FIFOAV_4WORDS) {
-		period_ms = DIV_ROUND_UP(pwm_get_period(pwm),
+		period_ms = DIV_ROUND_UP_ULL(pwm_get_period(pwm),
 					 NSEC_PER_MSEC);
 		msleep(period_ms);
 
@@ -213,6 +213,45 @@ static void pwm_imx27_wait_fifo_slot(struct pwm_chip *chip,
 	}
 }
 
+static int pwm_imx27_calc_period_cycles(const struct pwm_state *state,
+					unsigned long clk_rate,
+					unsigned long *period_cycles)
+{
+	u64 c = 0, c1, c2;
+
+	c1 = clk_rate;
+	c2 = state->period;
+	if (c2 > c1) {
+		c2 = c1;
+		c1 = state->period;
+	}
+
+	if (!c1 || !c2) {
+		pr_err("clk rate and period should be nonzero\n");
+		return -EINVAL;
+	}
+
+	if (c2 <= div64_u64(U64_MAX, c1)) {
+		c = c1 * c2;
+		do_div(c, 1000000000);
+	} else if (c2 <= div64_u64(U64_MAX, div64_u64(c1, 1000))) {
+		do_div(c1, 1000);
+		c = c1 * c2;
+		do_div(c, 1000000);
+	} else if (c2 <= div64_u64(U64_MAX, div64_u64(c1, 1000000))) {
+		do_div(c1, 1000000);
+		c = c1 * c2;
+		do_div(c, 1000);
+	} else if (c2 <= div64_u64(U64_MAX, div64_u64(c1, 1000000000))) {
+		do_div(c1, 1000000000);
+		c = c1 * c2;
+	}
+
+	*period_cycles = c;
+
+	return 0;
+}
+
 static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 			   const struct pwm_state *state)
 {
@@ -225,18 +264,16 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm,
 
 	pwm_get_state(pwm, &cstate);
 
-	c = clk_get_rate(imx->clk_per);
-	c *= state->period;
-
-	do_div(c, 1000000000);
-	period_cycles = c;
+	ret = pwm_imx27_calc_period_cycles(state, clk_get_rate(imx->clk_per),
+					   &period_cycles);
+	if (ret)
+		return ret;
 
 	prescale = period_cycles / 0x10000 + 1;
 
 	period_cycles /= prescale;
 	c = (unsigned long long)period_cycles * state->duty_cycle;
-	do_div(c, state->period);
-	duty_cycles = c;
+	duty_cycles = div64_u64(c, state->period);
 
 	/*
 	 * according to imx pwm RM, the real period value should be PERIOD
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project


  parent reply index

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-13  0:39 [RESEND PATCH v14 00/11] Convert PWM period and duty cycle to u64 Guru Das Srinagesh
2020-05-04 18:50 ` Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 01/11] drm/i915: Use 64-bit division macro Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 02/11] hwmon: pwm-fan: " Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 03/11] ir-rx51: " Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 04/11] pwm: clps711x: Cast period to u32 before use as divisor Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 05/11] pwm: pwm-imx-tpm: Use 64-bit division macro Guru Das Srinagesh
2020-05-04 18:50   ` Guru Das Srinagesh [this message]
2020-05-04 18:50   ` [RESEND PATCH v14 07/11] pwm: sifive: " Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 08/11] pwm: sun4i: Use nsecs_to_jiffies to avoid a division Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 09/11] backlight: pwm_bl: Use 64-bit division function Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 10/11] clk: pwm: " Guru Das Srinagesh
2020-05-04 18:50   ` [RESEND PATCH v14 11/11] pwm: core: Convert period and duty cycle to u64 Guru Das Srinagesh
2020-05-13  0:39   ` [RESEND PATCH v14 00/11] Convert PWM " Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 01/11] drm/i915: Use 64-bit division macro Guru Das Srinagesh
2020-05-20 22:55   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 02/11] hwmon: pwm-fan: " Guru Das Srinagesh
2020-05-20 22:55   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 03/11] ir-rx51: " Guru Das Srinagesh
2020-05-20 22:55   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 04/11] pwm: clps711x: Cast period to u32 before use as divisor Guru Das Srinagesh
2020-05-20 22:55   ` Guru Das Srinagesh
2020-05-21 10:19   ` Daniel Thompson
2020-05-21 20:25     ` Guru Das Srinagesh
2020-05-22  9:37       ` Daniel Thompson
2020-05-22 23:19         ` Guru Das Srinagesh
2020-05-23 17:08           ` Daniel Thompson
2020-05-13  0:39 ` [RESEND PATCH v14 05/11] pwm: pwm-imx-tpm: Use 64-bit division macro Guru Das Srinagesh
2020-05-20 22:55   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 06/11] pwm: imx27: Use 64-bit division macro and function Guru Das Srinagesh
2020-05-20 22:55   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 07/11] pwm: sifive: Use 64-bit division macro Guru Das Srinagesh
2020-05-20 22:56   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 08/11] pwm: sun4i: Use nsecs_to_jiffies to avoid a division Guru Das Srinagesh
2020-05-20 22:56   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 09/11] backlight: pwm_bl: Use 64-bit division function Guru Das Srinagesh
2020-05-20 22:56   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 10/11] clk: pwm: " Guru Das Srinagesh
2020-05-20 22:56   ` Guru Das Srinagesh
2020-05-13  0:39 ` [RESEND PATCH v14 11/11] pwm: core: Convert period and duty cycle to u64 Guru Das Srinagesh
2020-05-20 22:56   ` Guru Das Srinagesh
2020-05-20 22:55 ` [RESEND PATCH v14 00/11] Convert PWM " Guru Das Srinagesh

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