diff options
author | David Woodhouse <David.Woodhouse@intel.com> | 2008-07-25 10:40:14 -0400 |
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committer | David Woodhouse <David.Woodhouse@intel.com> | 2008-07-25 10:40:14 -0400 |
commit | ff877ea80efa2015b6263766f78ee42c2a1b32f9 (patch) | |
tree | 85205005c611ab774702148558321c6fb92f1ccd /arch/arm/mach-omap2/clock.c | |
parent | 30821fee4f0cb3e6d241d9f7ddc37742212e3eb7 (diff) | |
parent | d37e6bf68fc1eb34a4ad21d9ae8890ed37ea80e7 (diff) |
Merge branch 'linux-next' of git://git.infradead.org/~dedekind/ubi-2.6
Diffstat (limited to 'arch/arm/mach-omap2/clock.c')
-rw-r--r-- | arch/arm/mach-omap2/clock.c | 201 |
1 files changed, 199 insertions, 2 deletions
diff --git a/arch/arm/mach-omap2/clock.c b/arch/arm/mach-omap2/clock.c index ab9fc57d25f..15675bce801 100644 --- a/arch/arm/mach-omap2/clock.c +++ b/arch/arm/mach-omap2/clock.c @@ -41,6 +41,24 @@ #define MAX_CLOCK_ENABLE_WAIT 100000 +/* DPLL rate rounding: minimum DPLL multiplier, divider values */ +#define DPLL_MIN_MULTIPLIER 1 +#define DPLL_MIN_DIVIDER 1 + +/* Possible error results from _dpll_test_mult */ +#define DPLL_MULT_UNDERFLOW (1 << 0) + +/* + * 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)) + u8 cpu_mask; /*------------------------------------------------------------------------- @@ -95,7 +113,7 @@ u32 omap2_get_dpll_rate(struct clk *clk) { long long dpll_clk; u32 dpll_mult, dpll_div, dpll; - const struct dpll_data *dd; + struct dpll_data *dd; dd = clk->dpll_data; /* REVISIT: What do we return on error? */ @@ -603,7 +621,8 @@ int omap2_clksel_set_rate(struct clk *clk, unsigned long rate) clk->rate = clk->parent->rate / new_div; if (clk->flags & DELAYED_APP && cpu_is_omap24xx()) { - __raw_writel(OMAP24XX_VALID_CONFIG, OMAP24XX_PRCM_CLKCFG_CTRL); + prm_write_mod_reg(OMAP24XX_VALID_CONFIG, + OMAP24XX_GR_MOD, OMAP24XX_PRCM_CLKCFG_CTRL_OFFSET); wmb(); } @@ -723,6 +742,184 @@ int omap2_clk_set_parent(struct clk *clk, struct clk *new_parent) return 0; } +/* 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; +} + +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 flags = 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; + flags = DPLL_MULT_UNDERFLOW; + } + + if (*new_rate == 0) + *new_rate = _dpll_compute_new_rate(parent_rate, *m, n); + + return flags; +} + +/** + * 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; + + if (!clk || !clk->dpll_data) + return ~0; + + pr_debug("clock: starting DPLL round_rate for clock %s, target rate " + "%ld\n", clk->name, target_rate); + + scaled_rt_rp = target_rate / (clk->parent->rate / DPLL_SCALE_FACTOR); + scaled_max_m = clk->dpll_data->max_multiplier * DPLL_SCALE_FACTOR; + + clk->dpll_data->last_rounded_rate = 0; + + for (n = clk->dpll_data->max_divider; n >= DPLL_MIN_DIVIDER; n--) { + + /* Compute the scaled DPLL multiplier, based on the divider */ + m = scaled_rt_rp * n; + + /* + * Since we're counting n down, a m overflow means we can + * can immediately skip to the next n + */ + if (m > scaled_max_m) + continue; + + r = _dpll_test_mult(&m, n, &new_rate, target_rate, + clk->parent->rate); + + 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) - clk->dpll_data->rate_tolerance)) { + min_e = e; + min_e_m = m; + min_e_n = n; + + pr_debug("clock: found new least error %d\n", min_e); + } + + /* + * Since we're counting n down, a m underflow means we + * can bail out completely (since as n decreases in + * the next iteration, there's no way that m can + * increase beyond the current m) + */ + if (r & DPLL_MULT_UNDERFLOW) + break; + } + + if (min_e < 0) { + pr_debug("clock: error: target rate or tolerance too low\n"); + return ~0; + } + + clk->dpll_data->last_rounded_m = min_e_m; + clk->dpll_data->last_rounded_n = min_e_n; + clk->dpll_data->last_rounded_rate = + _dpll_compute_new_rate(clk->parent->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", + clk->dpll_data->last_rounded_rate, target_rate); + + return clk->dpll_data->last_rounded_rate; +} + /*------------------------------------------------------------------------- * Omap2 clock reset and init functions *-------------------------------------------------------------------------*/ |