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clkt_dpll.c

/*
 * OMAP2/3/4 DPLL clock functions
 *
 * Copyright (C) 2005-2008 Texas Instruments, Inc.
 * Copyright (C) 2004-2010 Nokia Corporation
 *
 * Contacts:
 * Richard Woodruff <r-woodruff2@ti.com>
 * Paul Walmsley
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#undef DEBUG

#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/clk.h>
#include <linux/io.h>

#include <asm/div64.h>

#include <plat/clock.h>

#include "clock.h"
#include "cm-regbits-24xx.h"
#include "cm-regbits-34xx.h"

/* DPLL rate rounding: minimum DPLL multiplier, divider values */
#define DPLL_MIN_MULTIPLIER         2
#define DPLL_MIN_DIVIDER            1

/* Possible error results from _dpll_test_mult */
#define DPLL_MULT_UNDERFLOW         -1

/*
 * Scale factor to mitigate roundoff errors in DPLL rate rounding.
 * The higher the scale factor, the greater the risk of arithmetic overflow,
 * but the closer the rounded rate to the target rate.  DPLL_SCALE_FACTOR
 * must be a power of DPLL_SCALE_BASE.
 */
#define DPLL_SCALE_FACTOR           64
#define DPLL_SCALE_BASE             2
#define DPLL_ROUNDING_VAL           ((DPLL_SCALE_BASE / 2) * \
                               (DPLL_SCALE_FACTOR / DPLL_SCALE_BASE))

/* DPLL valid Fint frequency band limits - from 34xx TRM Section 4.7.6.2 */
#define DPLL_FINT_BAND1_MIN         750000
#define DPLL_FINT_BAND1_MAX         2100000
#define DPLL_FINT_BAND2_MIN         7500000
#define DPLL_FINT_BAND2_MAX         21000000

/* _dpll_test_fint() return codes */
#define DPLL_FINT_UNDERFLOW         -1
#define DPLL_FINT_INVALID           -2

/* Private functions */

/*
 * _dpll_test_fint - test whether an Fint value is valid for the DPLL
 * @clk: DPLL struct clk to test
 * @n: divider value (N) to test
 *
 * Tests whether a particular divider @n will result in a valid DPLL
 * internal clock frequency Fint. See the 34xx TRM 4.7.6.2 "DPLL Jitter
 * Correction".  Returns 0 if OK, -1 if the enclosing loop can terminate
 * (assuming that it is counting N upwards), or -2 if the enclosing loop
 * should skip to the next iteration (again assuming N is increasing).
 */
static int _dpll_test_fint(struct clk *clk, u8 n)
{
      struct dpll_data *dd;
      long fint;
      int ret = 0;

      dd = clk->dpll_data;

      /* DPLL divider must result in a valid jitter correction val */
      fint = clk->parent->rate / (n + 1);
      if (fint < DPLL_FINT_BAND1_MIN) {

            pr_debug("rejecting n=%d due to Fint failure, "
                   "lowering max_divider\n", n);
            dd->max_divider = n;
            ret = DPLL_FINT_UNDERFLOW;

      } else if (fint > DPLL_FINT_BAND1_MAX &&
               fint < DPLL_FINT_BAND2_MIN) {

            pr_debug("rejecting n=%d due to Fint failure\n", n);
            ret = DPLL_FINT_INVALID;

      } else if (fint > DPLL_FINT_BAND2_MAX) {

            pr_debug("rejecting n=%d due to Fint failure, "
                   "boosting min_divider\n", n);
            dd->min_divider = n;
            ret = DPLL_FINT_INVALID;

      }

      return ret;
}

static unsigned long _dpll_compute_new_rate(unsigned long parent_rate,
                                  unsigned int m, unsigned int n)
{
      unsigned long long num;

      num = (unsigned long long)parent_rate * m;
      do_div(num, n);
      return num;
}

/*
 * _dpll_test_mult - test a DPLL multiplier value
 * @m: pointer to the DPLL m (multiplier) value under test
 * @n: current DPLL n (divider) value under test
 * @new_rate: pointer to storage for the resulting rounded rate
 * @target_rate: the desired DPLL rate
 * @parent_rate: the DPLL's parent clock rate
 *
 * This code tests a DPLL multiplier value, ensuring that the
 * resulting rate will not be higher than the target_rate, and that
 * the multiplier value itself is valid for the DPLL.  Initially, the
 * integer pointed to by the m argument should be prescaled by
 * multiplying by DPLL_SCALE_FACTOR.  The code will replace this with
 * a non-scaled m upon return.  This non-scaled m will result in a
 * new_rate as close as possible to target_rate (but not greater than
 * target_rate) given the current (parent_rate, n, prescaled m)
 * triple. Returns DPLL_MULT_UNDERFLOW in the event that the
 * non-scaled m attempted to underflow, which can allow the calling
 * function to bail out early; or 0 upon success.
 */
static int _dpll_test_mult(int *m, int n, unsigned long *new_rate,
                     unsigned long target_rate,
                     unsigned long parent_rate)
{
      int r = 0, carry = 0;

      /* Unscale m and round if necessary */
      if (*m % DPLL_SCALE_FACTOR >= DPLL_ROUNDING_VAL)
            carry = 1;
      *m = (*m / DPLL_SCALE_FACTOR) + carry;

      /*
       * The new rate must be <= the target rate to avoid programming
       * a rate that is impossible for the hardware to handle
       */
      *new_rate = _dpll_compute_new_rate(parent_rate, *m, n);
      if (*new_rate > target_rate) {
            (*m)--;
            *new_rate = 0;
      }

      /* Guard against m underflow */
      if (*m < DPLL_MIN_MULTIPLIER) {
            *m = DPLL_MIN_MULTIPLIER;
            *new_rate = 0;
            r = DPLL_MULT_UNDERFLOW;
      }

      if (*new_rate == 0)
            *new_rate = _dpll_compute_new_rate(parent_rate, *m, n);

      return r;
}

/* Public functions */

void omap2_init_dpll_parent(struct clk *clk)
{
      u32 v;
      struct dpll_data *dd;

      dd = clk->dpll_data;
      if (!dd)
            return;

      /* Return bypass rate if DPLL is bypassed */
      v = __raw_readl(dd->control_reg);
      v &= dd->enable_mask;
      v >>= __ffs(dd->enable_mask);

      /* Reparent in case the dpll is in bypass */
      if (cpu_is_omap24xx()) {
            if (v == OMAP2XXX_EN_DPLL_LPBYPASS ||
                v == OMAP2XXX_EN_DPLL_FRBYPASS)
                  clk_reparent(clk, dd->clk_bypass);
      } else if (cpu_is_omap34xx()) {
            if (v == OMAP3XXX_EN_DPLL_LPBYPASS ||
                v == OMAP3XXX_EN_DPLL_FRBYPASS)
                  clk_reparent(clk, dd->clk_bypass);
      } else if (cpu_is_omap44xx()) {
            if (v == OMAP4XXX_EN_DPLL_LPBYPASS ||
                v == OMAP4XXX_EN_DPLL_FRBYPASS ||
                v == OMAP4XXX_EN_DPLL_MNBYPASS)
                  clk_reparent(clk, dd->clk_bypass);
      }
      return;
}

/**
 * omap2_get_dpll_rate - returns the current DPLL CLKOUT rate
 * @clk: struct clk * of a DPLL
 *
 * DPLLs can be locked or bypassed - basically, enabled or disabled.
 * When locked, the DPLL output depends on the M and N values.  When
 * bypassed, on OMAP2xxx, the output rate is either the 32KiHz clock
 * or sys_clk.  Bypass rates on OMAP3 depend on the DPLL: DPLLs 1 and
 * 2 are bypassed with dpll1_fclk and dpll2_fclk respectively
 * (generated by DPLL3), while DPLL 3, 4, and 5 bypass rates are sys_clk.
 * Returns the current DPLL CLKOUT rate (*not* CLKOUTX2) if the DPLL is
 * locked, or the appropriate bypass rate if the DPLL is bypassed, or 0
 * if the clock @clk is not a DPLL.
 */
u32 omap2_get_dpll_rate(struct clk *clk)
{
      long long dpll_clk;
      u32 dpll_mult, dpll_div, v;
      struct dpll_data *dd;

      dd = clk->dpll_data;
      if (!dd)
            return 0;

      /* Return bypass rate if DPLL is bypassed */
      v = __raw_readl(dd->control_reg);
      v &= dd->enable_mask;
      v >>= __ffs(dd->enable_mask);

      if (cpu_is_omap24xx()) {
            if (v == OMAP2XXX_EN_DPLL_LPBYPASS ||
                v == OMAP2XXX_EN_DPLL_FRBYPASS)
                  return dd->clk_bypass->rate;
      } else if (cpu_is_omap34xx()) {
            if (v == OMAP3XXX_EN_DPLL_LPBYPASS ||
                v == OMAP3XXX_EN_DPLL_FRBYPASS)
                  return dd->clk_bypass->rate;
      } else if (cpu_is_omap44xx()) {
            if (v == OMAP4XXX_EN_DPLL_LPBYPASS ||
                v == OMAP4XXX_EN_DPLL_FRBYPASS ||
                v == OMAP4XXX_EN_DPLL_MNBYPASS)
                  return dd->clk_bypass->rate;
      }

      v = __raw_readl(dd->mult_div1_reg);
      dpll_mult = v & dd->mult_mask;
      dpll_mult >>= __ffs(dd->mult_mask);
      dpll_div = v & dd->div1_mask;
      dpll_div >>= __ffs(dd->div1_mask);

      dpll_clk = (long long)dd->clk_ref->rate * dpll_mult;
      do_div(dpll_clk, dpll_div + 1);

      return dpll_clk;
}

/* DPLL rate rounding code */

/**
 * omap2_dpll_set_rate_tolerance: set the error tolerance during rate rounding
 * @clk: struct clk * of the DPLL
 * @tolerance: maximum rate error tolerance
 *
 * Set the maximum DPLL rate error tolerance for the rate rounding
 * algorithm.  The rate tolerance is an attempt to balance DPLL power
 * saving (the least divider value "n") vs. rate fidelity (the least
 * difference between the desired DPLL target rate and the rounded
 * rate out of the algorithm).  So, increasing the tolerance is likely
 * to decrease DPLL power consumption and increase DPLL rate error.
 * Returns -EINVAL if provided a null clock ptr or a clk that is not a
 * DPLL; or 0 upon success.
 */
int omap2_dpll_set_rate_tolerance(struct clk *clk, unsigned int tolerance)
{
      if (!clk || !clk->dpll_data)
            return -EINVAL;

      clk->dpll_data->rate_tolerance = tolerance;

      return 0;
}

/**
 * omap2_dpll_round_rate - round a target rate for an OMAP DPLL
 * @clk: struct clk * for a DPLL
 * @target_rate: desired DPLL clock rate
 *
 * Given a DPLL, a desired target rate, and a rate tolerance, round
 * the target rate to a possible, programmable rate for this DPLL.
 * Rate tolerance is assumed to be set by the caller before this
 * function is called.  Attempts to select the minimum possible n
 * within the tolerance to reduce power consumption.  Stores the
 * computed (m, n) in the DPLL's dpll_data structure so set_rate()
 * will not need to call this (expensive) function again.  Returns ~0
 * if the target rate cannot be rounded, either because the rate is
 * too low or because the rate tolerance is set too tightly; or the
 * rounded rate upon success.
 */
long omap2_dpll_round_rate(struct clk *clk, unsigned long target_rate)
{
      int m, n, r, e, scaled_max_m;
      unsigned long scaled_rt_rp, new_rate;
      int min_e = -1, min_e_m = -1, min_e_n = -1;
      struct dpll_data *dd;

      if (!clk || !clk->dpll_data)
            return ~0;

      dd = clk->dpll_data;

      pr_debug("clock: starting DPLL round_rate for clock %s, target rate "
             "%ld\n", clk->name, target_rate);

      scaled_rt_rp = target_rate / (dd->clk_ref->rate / DPLL_SCALE_FACTOR);
      scaled_max_m = dd->max_multiplier * DPLL_SCALE_FACTOR;

      dd->last_rounded_rate = 0;

      for (n = dd->min_divider; n <= dd->max_divider; n++) {

            /* Is the (input clk, divider) pair valid for the DPLL? */
            r = _dpll_test_fint(clk, n);
            if (r == DPLL_FINT_UNDERFLOW)
                  break;
            else if (r == DPLL_FINT_INVALID)
                  continue;

            /* Compute the scaled DPLL multiplier, based on the divider */
            m = scaled_rt_rp * n;

            /*
             * Since we're counting n up, a m overflow means we
             * can bail out completely (since as n increases in
             * the next iteration, there's no way that m can
             * increase beyond the current m)
             */
            if (m > scaled_max_m)
                  break;

            r = _dpll_test_mult(&m, n, &new_rate, target_rate,
                            dd->clk_ref->rate);

            /* m can't be set low enough for this n - try with a larger n */
            if (r == DPLL_MULT_UNDERFLOW)
                  continue;

            e = target_rate - new_rate;
            pr_debug("clock: n = %d: m = %d: rate error is %d "
                   "(new_rate = %ld)\n", n, m, e, new_rate);

            if (min_e == -1 ||
                min_e >= (int)(abs(e) - dd->rate_tolerance)) {
                  min_e = e;
                  min_e_m = m;
                  min_e_n = n;

                  pr_debug("clock: found new least error %d\n", min_e);

                  /* We found good settings -- bail out now */
                  if (min_e <= dd->rate_tolerance)
                        break;
            }
      }

      if (min_e < 0) {
            pr_debug("clock: error: target rate or tolerance too low\n");
            return ~0;
      }

      dd->last_rounded_m = min_e_m;
      dd->last_rounded_n = min_e_n;
      dd->last_rounded_rate = _dpll_compute_new_rate(dd->clk_ref->rate,
                                           min_e_m,  min_e_n);

      pr_debug("clock: final least error: e = %d, m = %d, n = %d\n",
             min_e, min_e_m, min_e_n);
      pr_debug("clock: final rate: %ld  (target rate: %ld)\n",
             dd->last_rounded_rate, target_rate);

      return dd->last_rounded_rate;
}


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