/*
* Aptina Sensor PLL Configuration
*
* Copyright (C) 2012 Laurent Pinchart <laurent.pinchart@ideasonboard.com>
*
* 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.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA
*/
#include <linux/device.h>
#include <linux/gcd.h>
#include <linux/kernel.h>
#include <linux/lcm.h>
#include <linux/module.h>
#include "aptina-pll.h"
int aptina_pll_calculate(struct device *dev,
const struct aptina_pll_limits *limits,
struct aptina_pll *pll)
{
unsigned int mf_min;
unsigned int mf_max;
unsigned int p1_min;
unsigned int p1_max;
unsigned int p1;
unsigned int div;
dev_dbg(dev, "PLL: ext clock %u pix clock %u\n",
pll->ext_clock, pll->pix_clock);
if (pll->ext_clock < limits->ext_clock_min ||
pll->ext_clock > limits->ext_clock_max) {
dev_err(dev, "pll: invalid external clock frequency.\n");
return -EINVAL;
}
if (pll->pix_clock == 0 || pll->pix_clock > limits->pix_clock_max) {
dev_err(dev, "pll: invalid pixel clock frequency.\n");
return -EINVAL;
}
/* Compute the multiplier M and combined N*P1 divisor. */
div = gcd(pll->pix_clock, pll->ext_clock);
pll->m = pll->pix_clock / div;
div = pll->ext_clock / div;
/* We now have the smallest M and N*P1 values that will result in the
* desired pixel clock frequency, but they might be out of the valid
* range. Compute the factor by which we should multiply them given the
* following constraints:
*
* - minimum/maximum multiplier
* - minimum/maximum multiplier output clock frequency assuming the
* minimum/maximum N value
* - minimum/maximum combined N*P1 divisor
*/
mf_min = DIV_ROUND_UP(limits->m_min, pll->m);
mf_min = max(mf_min, limits->out_clock_min /
(pll->ext_clock / limits->n_min * pll->m));
mf_min = max(mf_min, limits->n_min * limits->p1_min / div);
mf_max = limits->m_max / pll->m;
mf_max = min(mf_max, limits->out_clock_max /
(pll->ext_clock / limits->n_max * pll->m));
mf_max = min(mf_max, DIV_ROUND_UP(limits->n_max * limits->p1_max, div));
dev_dbg(dev, "pll: mf min %u max %u\n", mf_min, mf_max);
if (mf_min > mf_max) {
dev_err(dev, "pll: no valid combined N*P1 divisor.\n");
return -EINVAL;
}
/*
* We're looking for the highest acceptable P1 value for which a
* multiplier factor MF exists that fulfills the following conditions:
*
* 1. p1 is in the [p1_min, p1_max] range given by the limits and is
* even
* 2. mf is in the [mf_min, mf_max] range computed above
* 3. div * mf is a multiple of p1, in order to compute
* n = div * mf / p1
* m = pll->m * mf
* 4. the internal clock frequency, given by ext_clock / n, is in the
* [int_clock_min, int_clock_max] range given by the limits
* 5. the output clock frequency, given by ext_clock / n * m, is in the
* [out_clock_min, out_clock_max] range given by the limits
*
* The first naive approach is to iterate over all p1 values acceptable
* according to (1) and all mf values acceptable according to (2), and
* stop at the first combination that fulfills (3), (4) and (5). This
* has a O(n^2) complexity.
*
* Instead of iterating over all mf values in the [mf_min, mf_max] range
* we can compute the mf increment between two acceptable values
* according to (3) with
*
* mf_inc = p1 / gcd(div, p1) (6)
*
* and round the minimum up to the nearest multiple of mf_inc. This will
* restrict the number of mf values to be checked.
*
* Furthermore, conditions (4) and (5) only restrict the range of
* acceptable p1 and mf values by modifying the minimum and maximum
* limits. (5) can be expressed as
*
* ext_clock / (div * mf / p1) * m * mf >= out_clock_min
* ext_clock / (div * mf / p1) * m * mf <= out_clock_max
*
* or
*
* p1 >= out_clock_min * div / (ext_clock * m) (7)
* p1 <= out_clock_max * div / (ext_clock * m)
*
* Similarly, (4) can be expressed as
*
* mf >= ext_clock * p1 / (int_clock_max * div) (8)
* mf <= ext_clock * p1 / (int_clock_min * div)
*
* We can thus iterate over the restricted p1 range defined by the
* combination of (1) and (7), and then compute the restricted mf range
* defined by the combination of (2), (6) and (8). If the resulting mf
* range is not empty, any value in the mf range is acceptable. We thus
* select the mf lwoer bound and the corresponding p1 value.
*/
if (limits->p1_min == 0) {
dev_err(dev, "pll: P1 minimum value must be >0.\n");
return -EINVAL;
}
p1_min = max(limits->p1_min, DIV_ROUND_UP(limits->out_clock_min * div,
pll->ext_clock * pll->m));
p1_max = min(limits->p1_max, limits->out_clock_max * div /
(pll->ext_clock * pll->m));
for (p1 = p1_max & ~1; p1 >= p1_min; p1 -= 2) {
unsigned int mf_inc = p1 / gcd(div, p1);
unsigned int mf_high;
unsigned int mf_low;
mf_low = max(roundup(mf_min, mf_inc),
DIV_ROUND_UP(pll->ext_clock * p1,
limits->int_clock_max * div));
mf_high = min(mf_max, pll->ext_clock * p1 /
(limits->int_clock_min * div));
if (mf_low > mf_high)
continue;
pll->n = div * mf_low / p1;
pll->m *= mf_low;
pll->p1 = p1;
dev_dbg(dev, "PLL: N %u M %u P1 %u\n", pll->n, pll->m, pll->p1);
return 0;
}
dev_err(dev, "pll: no valid N and P1 divisors found.\n");
return -EINVAL;
}
EXPORT_SYMBOL_GPL(aptina_pll_calculate);
MODULE_DESCRIPTION("Aptina PLL Helpers");
MODULE_AUTHOR("Laurent Pinchart <laurent.pinchart@ideasonboard.com>");
MODULE_LICENSE("GPL v2");
