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    Subject[PATCH v16 06/11] pwm: imx27: Use 64-bit division macro and function
    Date
    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 <shawnguo@kernel.org>
    Cc: Sascha Hauer <s.hauer@pengutronix.de>
    Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
    Cc: Fabio Estevam <festevam@gmail.com>
    Cc: NXP Linux Team <linux-imx@nxp.com>
    Signed-off-by: Guru Das Srinagesh <gurus@codeaurora.org>
    ---
    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
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