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