From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guru Das Srinagesh Subject: [PATCH v16 06/11] pwm: imx27: Use 64-bit division macro and function Date: Tue, 2 Jun 2020 15:31:10 -0700 Message-ID: References: Return-path: In-Reply-To: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org To: linux-pwm@vger.kernel.org, Thierry Reding , =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?= Cc: Subbaraman Narayanamurthy , David Collins , linux-kernel@vger.kernel.org, Joe Perches , Stephen Boyd , Lee Jones , Arnd Bergmann , Geert Uytterhoeven , Guenter Roeck , Daniel Thompson , Dan Carpenter , linux-arm-kernel@lists.infradead.org, Guru Das Srinagesh , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , NXP Linux Team List-Id: linux-pwm@vger.kernel.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. Cc: Shawn Guo Cc: Sascha Hauer Cc: Pengutronix Kernel Team Cc: Fabio Estevam Cc: NXP Linux Team Signed-off-by: Guru Das Srinagesh --- drivers/pwm/pwm-imx27.c | 48 +++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 43 insertions(+), 5 deletions(-) diff --git a/drivers/pwm/pwm-imx27.c b/drivers/pwm/pwm-imx27.c index 732a6f3..147729d 100644 --- a/drivers/pwm/pwm-imx27.c +++ b/drivers/pwm/pwm-imx27.c @@ -202,7 +202,7 @@ 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); @@ -212,6 +212,45 @@ 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) { @@ -226,10 +265,9 @@ static int pwm_imx27_apply(struct pwm_chip *chip, struct pwm_device *pwm, pwm_get_state(pwm, &cstate); clkrate = clk_get_rate(imx->clk_per); - c = clkrate * state->period; - - do_div(c, NSEC_PER_SEC); - period_cycles = c; + ret = pwm_imx27_calc_period_cycles(state, clkrate, &period_cycles); + if (ret) + return ret; prescale = period_cycles / 0x10000 + 1; -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project