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Date: Mon, 2 May 2011 16:58:56 +0200
From: Samuel Ortiz <sameo@...ux.intel.com>
To: Willie Ruan <wruan@...eaurora.org>
Cc: David Brown <davidb@...eaurora.org>,
Daniel Walker <dwalker@...o99.com>,
Bryan Huntsman <bryanh@...eaurora.org>,
linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH 1/2] mfd: pm8xxx-pwm: add pm8xxx PWM driver
Hi Willie,
On Thu, Apr 21, 2011 at 11:15:51PM -0700, Willie Ruan wrote:
> Qualcomm PM8xxx chips, such as PM8058 and PM8921, have 8 channels of
> PWM, also called LPG (Light Pulse Generator) in HW specs. All PWM
> channels can be used as simple PWM machine or as a more advanced PWM
> pattern generator using programmed lookup table.
>
> This patch supports all APIs listed in <linux/pwm.h> with a small
> difference. The two parameters (duty_ns and period_ns) in pwm_config()
> are used as values in microseconds instead of nanoseconds. Otherwise a
> 32-bit integer can't fit for a range of 7 us to 300+ seconds.
I can only lament the fact that we're still lacking a proper PWM API. Besides
that, I have a couple comments:
> +static void pm8xxx_pwm_calc_period(unsigned int period_us,
> + struct pm8xxx_pwm_config *pwm_conf)
> +{
> + int n, m, clk, div;
> + int best_m, best_div, best_clk;
> + int last_err, cur_err, better_err, better_m;
> + unsigned int tmp_p, last_p, min_err, period_n;
> +
> + /* PWM Period / N */
> + if (period_us < (40 * USEC_PER_SEC)) { /* ~6-bit max */
> + period_n = (period_us * NSEC_PER_USEC) >> 6;
> + n = 6;
> + } else if (period_us < (274 * USEC_PER_SEC)) { /* overflow threshold */
> + period_n = (period_us >> 6) * NSEC_PER_USEC;
> + if (period_n >= MAX_MPT) {
> + n = 9;
> + period_n >>= 3;
> + } else
> + n = 6;
> + } else {
> + period_n = (period_us >> 9) * NSEC_PER_USEC;
> + n = 9;
> + }
> +
> + min_err = MAX_MPT;
> + best_m = 0;
> + best_clk = 0;
> + best_div = 0;
> + for (clk = 0; clk < NUM_CLOCKS; clk++) {
> + for (div = 0; div < NUM_PRE_DIVIDE; div++) {
> + tmp_p = period_n;
> + last_p = tmp_p;
> + for (m = 0; m <= PM8XXX_PWM_M_MAX; m++) {
> + if (tmp_p <= pt_t[div][clk]) {
> + /* Found local best */
> + if (!m) {
> + better_err = pt_t[div][clk] -
> + tmp_p;
> + better_m = m;
> + } else {
> + last_err = last_p -
> + pt_t[div][clk];
> + cur_err = pt_t[div][clk] -
> + tmp_p;
> +
> + if (cur_err < last_err) {
> + better_err = cur_err;
> + better_m = m;
> + } else {
> + better_err = last_err;
> + better_m = m - 1;
> + }
> + }
> +
> + if (better_err < min_err) {
> + min_err = better_err;
> + best_m = better_m;
> + best_clk = clk;
> + best_div = div;
> + }
> + break;
> + } else {
> + last_p = tmp_p;
> + tmp_p >>= 1;
> + }
> + }
> + }
> + }
This loop needs to be splitted up into 2-3 different routines. Your code will
be much more readable.
> +static int pm8xxx_pwm_configure(struct pwm_device *pwm,
> + struct pm8xxx_pwm_config *pwm_conf)
> +{
> + int i, rc, len;
> + u8 reg, ramp_enabled = 0;
> +
> + reg = (pwm_conf->pwm_size > 6) ? PM8XXX_PWM_SIZE_9_BIT : 0;
> + pwm->pwm_ctl[5] = reg;
> +
> + reg = ((pwm_conf->clk + 1) << PM8XXX_PWM_CLK_SEL_SHIFT)
> + & PM8XXX_PWM_CLK_SEL_MASK;
> + reg |= (pwm_conf->pre_div << PM8XXX_PWM_PREDIVIDE_SHIFT)
> + & PM8XXX_PWM_PREDIVIDE_MASK;
> + reg |= pwm_conf->pre_div_exp & PM8XXX_PWM_M_MASK;
> + pwm->pwm_ctl[4] = reg;
> +
> + if (pwm_conf->bypass_lut) {
> + pwm->pwm_ctl[0] &= PM8XXX_PWM_PWM_START; /* keep enabled */
> + pwm->pwm_ctl[1] = PM8XXX_PWM_BYPASS_LUT;
> + pwm->pwm_ctl[2] = 0;
> +
> + if (pwm_conf->pwm_size > 6) {
> + pwm->pwm_ctl[3] = pwm_conf->pwm_value
> + & PM8XXX_PWM_VALUE_BIT7_0;
> + pwm->pwm_ctl[4] |= (pwm_conf->pwm_value >> 1)
> + & PM8XXX_PWM_VALUE_BIT8;
> + } else {
> + pwm->pwm_ctl[3] = pwm_conf->pwm_value
> + & PM8XXX_PWM_VALUE_BIT5_0;
> + }
> +
> + len = 6;
> + } else {
> + int pause_cnt, j;
> +
> + /* Linear search for duty time */
> + for (i = 0; i < PM8XXX_PWM_1KHZ_COUNT_MAX; i++) {
> + if (duty_msec[i] >= pwm_conf->lut_duty_ms)
> + break;
> + }
> +
> + ramp_enabled = pwm->pwm_ctl[0] & PM8XXX_PWM_RAMP_GEN_START;
> + pwm->pwm_ctl[0] &= PM8XXX_PWM_PWM_START; /* keep enabled */
> + pwm->pwm_ctl[0] |= (i << PM8XXX_PWM_1KHZ_COUNT_SHIFT) &
> + PM8XXX_PWM_1KHZ_COUNT_MASK;
> + pwm->pwm_ctl[1] = pwm_conf->lut_hi_index &
> + PM8XXX_PWM_HIGH_INDEX_MASK;
> + pwm->pwm_ctl[2] = pwm_conf->lut_lo_index &
> + PM8XXX_PWM_LOW_INDEX_MASK;
> +
> + if (pwm_conf->flags & PM_PWM_LUT_REVERSE)
> + pwm->pwm_ctl[1] |= PM8XXX_PWM_REVERSE_EN;
> + if (pwm_conf->flags & PM_PWM_LUT_RAMP_UP)
> + pwm->pwm_ctl[2] |= PM8XXX_PWM_RAMP_UP;
> + if (pwm_conf->flags & PM_PWM_LUT_LOOP)
> + pwm->pwm_ctl[2] |= PM8XXX_PWM_LOOP_EN;
> +
> + /* Pause time */
> + if (pwm_conf->flags & PM_PWM_LUT_PAUSE_HI_EN) {
> + /* Linear search for pause time */
> + pause_cnt = (pwm_conf->lut_pause_hi + duty_msec[i] / 2)
> + / duty_msec[i];
> + for (j = 0; j < PM8XXX_PWM_PAUSE_COUNT_MAX; j++) {
> + if (pause_count[j] >= pause_cnt)
> + break;
> + }
> + pwm->pwm_ctl[5] = (j <<
> + PM8XXX_PWM_PAUSE_COUNT_HI_SHIFT) &
> + PM8XXX_PWM_PAUSE_COUNT_HI_MASK;
> + pwm->pwm_ctl[5] |= PM8XXX_PWM_PAUSE_ENABLE_HIGH;
> + } else
> + pwm->pwm_ctl[5] = 0;
> +
> + if (pwm_conf->flags & PM_PWM_LUT_PAUSE_LO_EN) {
> + /* Linear search for pause time */
> + pause_cnt = (pwm_conf->lut_pause_lo + duty_msec[i] / 2)
> + / duty_msec[i];
> + for (j = 0; j < PM8XXX_PWM_PAUSE_COUNT_MAX; j++) {
> + if (pause_count[j] >= pause_cnt)
> + break;
> + }
> + pwm->pwm_ctl[6] = (j <<
> + PM8XXX_PWM_PAUSE_COUNT_LO_SHIFT) &
> + PM8XXX_PWM_PAUSE_COUNT_LO_MASK;
> + pwm->pwm_ctl[6] |= PM8XXX_PWM_PAUSE_ENABLE_LOW;
> + } else
> + pwm->pwm_ctl[6] = 0;
> +
> + len = 7;
> + }
> +
> + pm8xxx_pwm_bank_sel(pwm);
> +
> + for (i = 0; i < len; i++) {
> + rc = pm8xxx_writeb(pwm->chip->dev->parent,
> + SSBI_REG_ADDR_LPG_CTL(i),
> + pwm->pwm_ctl[i]);
> + if (rc) {
> + pr_err("pm8xxx_write(): rc=%d (PWM Ctl[%d])\n", rc, i);
> + break;
> + }
> + }
> +
> + if (ramp_enabled) {
> + pwm->pwm_ctl[0] |= ramp_enabled;
> + pm8xxx_writeb(pwm->chip->dev->parent,
> + SSBI_REG_ADDR_LPG_CTL(0),
> + pwm->pwm_ctl[0]);
> + }
> +
> + return rc;
> +}
I would also appreciate if this routine could be made smaller by having it
calling sub routines.
Cheers,
Samuel.
--
Intel Open Source Technology Centre
http://oss.intel.com/
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