drivers/clk/clk-fractional-divider.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Copyright (C) 2014 Intel Corporation
   4  *
   5  * Adjustable fractional divider clock implementation.
   6  * Uses rational best approximation algorithm.
   7  *
   8  * Output is calculated as
   9  *
  10  *      rate = (m / n) * parent_rate                            (1)
  11  *
  12  * This is useful when we have a prescaler block which asks for
  13  * m (numerator) and n (denominator) values to be provided to satisfy
  14  * the (1) as much as possible.
  15  *
  16  * Since m and n have the limitation by a range, e.g.
  17  *
  18  *      n >= 1, n < N_width, where N_width = 2^nwidth           (2)
  19  *
  20  * for some cases the output may be saturated. Hence, from (1) and (2),
  21  * assuming the worst case when m = 1, the inequality
  22  *
  23  *      floor(log2(parent_rate / rate)) <= nwidth               (3)
  24  *
  25  * may be derived. Thus, in cases when
  26  *
  27  *      (parent_rate / rate) >> N_width                         (4)
  28  *
  29  * we might scale up the rate by 2^scale (see the description of
  30  * CLK_FRAC_DIVIDER_POWER_OF_TWO_PS for additional information), where
  31  *
  32  *      scale = floor(log2(parent_rate / rate)) - nwidth        (5)
  33  *
  34  * and assume that the IP, that needs m and n, has also its own
  35  * prescaler, which is capable to divide by 2^scale. In this way
  36  * we get the denominator to satisfy the desired range (2) and
  37  * at the same time a much better result of m and n than simple
  38  * saturated values.
  39  */
  40
  41 #include <linux/debugfs.h>
  42 #include <linux/device.h>
  43 #include <linux/io.h>
  44 #include <linux/math.h>
  45 #include <linux/module.h>
  46 #include <linux/rational.h>
  47 #include <linux/slab.h>
  48
  49 #include <linux/clk-provider.h>
  50
  51 #include "clk-fractional-divider.h"
  52
  53 static inline u32 clk_fd_readl(struct clk_fractional_divider *fd)
  54 {
  55         if (fd->flags & CLK_FRAC_DIVIDER_BIG_ENDIAN)
  56                 return ioread32be(fd->reg);
  57
  58         return readl(fd->reg);
  59 }
  60
  61 static inline void clk_fd_writel(struct clk_fractional_divider *fd, u32 val)
  62 {
  63         if (fd->flags & CLK_FRAC_DIVIDER_BIG_ENDIAN)
  64                 iowrite32be(val, fd->reg);
  65         else
  66                 writel(val, fd->reg);
  67 }
  68
  69 static void clk_fd_get_div(struct clk_hw *hw, struct u32_fract *fract)
  70 {
  71         struct clk_fractional_divider *fd = to_clk_fd(hw);
  72         unsigned long flags = 0;
  73         unsigned long m, n;
  74         u32 mmask, nmask;
  75         u32 val;
  76
  77         if (fd->lock)
  78                 spin_lock_irqsave(fd->lock, flags);
  79         else
  80                 __acquire(fd->lock);
  81
  82         val = clk_fd_readl(fd);
  83
  84         if (fd->lock)
  85                 spin_unlock_irqrestore(fd->lock, flags);
  86         else
  87                 __release(fd->lock);
  88
  89         mmask = GENMASK(fd->mwidth - 1, 0) << fd->mshift;
  90         nmask = GENMASK(fd->nwidth - 1, 0) << fd->nshift;
  91
  92         m = (val & mmask) >> fd->mshift;
  93         n = (val & nmask) >> fd->nshift;
  94
  95         if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
  96                 m++;
  97                 n++;
  98         }
  99
 100         fract->numerator = m;
 101         fract->denominator = n;
 102 }
 103
 104 static unsigned long clk_fd_recalc_rate(struct clk_hw *hw, unsigned long parent_rate)
 105 {
 106         struct u32_fract fract;
 107         u64 ret;
 108
 109         clk_fd_get_div(hw, &fract);
 110
 111         if (!fract.numerator || !fract.denominator)
 112                 return parent_rate;
 113
 114         ret = (u64)parent_rate * fract.numerator;
 115         do_div(ret, fract.denominator);
 116
 117         return ret;
 118 }
 119
 120 void clk_fractional_divider_general_approximation(struct clk_hw *hw,
 121                                                   unsigned long rate,
 122                                                   unsigned long *parent_rate,
 123                                                   unsigned long *m, unsigned long *n)
 124 {
 125         struct clk_fractional_divider *fd = to_clk_fd(hw);
 126         unsigned long max_m, max_n;
 127
 128         /*
 129          * Get rate closer to *parent_rate to guarantee there is no overflow
 130          * for m and n. In the result it will be the nearest rate left shifted
 131          * by (scale - fd->nwidth) bits.
 132          *
 133          * For the detailed explanation see the top comment in this file.
 134          */
 135         if (fd->flags & CLK_FRAC_DIVIDER_POWER_OF_TWO_PS) {
 136                 unsigned long scale = fls_long(*parent_rate / rate - 1);
 137
 138                 if (scale > fd->nwidth)
 139                         rate <<= scale - fd->nwidth;
 140         }
 141
 142         if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
 143                 max_m = BIT(fd->mwidth);
 144                 max_n = BIT(fd->nwidth);
 145         } else {
 146                 max_m = GENMASK(fd->mwidth - 1, 0);
 147                 max_n = GENMASK(fd->nwidth - 1, 0);
 148         }
 149
 150         rational_best_approximation(rate, *parent_rate, max_m, max_n, m, n);
 151 }
 152 EXPORT_SYMBOL_GPL(clk_fractional_divider_general_approximation);
 153
 154 static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
 155                               unsigned long *parent_rate)
 156 {
 157         struct clk_fractional_divider *fd = to_clk_fd(hw);
 158         unsigned long m, n;
 159         u64 ret;
 160
 161         if (!rate || (!clk_hw_can_set_rate_parent(hw) && rate >= *parent_rate))
 162                 return *parent_rate;
 163
 164         if (fd->approximation)
 165                 fd->approximation(hw, rate, parent_rate, &m, &n);
 166         else
 167                 clk_fractional_divider_general_approximation(hw, rate, parent_rate, &m, &n);
 168
 169         ret = (u64)*parent_rate * m;
 170         do_div(ret, n);
 171
 172         return ret;
 173 }
 174
 175 static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
 176                            unsigned long parent_rate)
 177 {
 178         struct clk_fractional_divider *fd = to_clk_fd(hw);
 179         unsigned long flags = 0;
 180         unsigned long m, n, max_m, max_n;
 181         u32 mmask, nmask;
 182         u32 val;
 183
 184         if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
 185                 max_m = BIT(fd->mwidth);
 186                 max_n = BIT(fd->nwidth);
 187         } else {
 188                 max_m = GENMASK(fd->mwidth - 1, 0);
 189                 max_n = GENMASK(fd->nwidth - 1, 0);
 190         }
 191         rational_best_approximation(rate, parent_rate, max_m, max_n, &m, &n);
 192
 193         if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
 194                 m--;
 195                 n--;
 196         }
 197
 198         mmask = GENMASK(fd->mwidth - 1, 0) << fd->mshift;
 199         nmask = GENMASK(fd->nwidth - 1, 0) << fd->nshift;
 200
 201         if (fd->lock)
 202                 spin_lock_irqsave(fd->lock, flags);
 203         else
 204                 __acquire(fd->lock);
 205
 206         val = clk_fd_readl(fd);
 207         val &= ~(mmask | nmask);
 208         val |= (m << fd->mshift) | (n << fd->nshift);
 209         clk_fd_writel(fd, val);
 210
 211         if (fd->lock)
 212                 spin_unlock_irqrestore(fd->lock, flags);
 213         else
 214                 __release(fd->lock);
 215
 216         return 0;
 217 }
 218
 219 #ifdef CONFIG_DEBUG_FS
 220 static int clk_fd_numerator_get(void *hw, u64 *val)
 221 {
 222         struct u32_fract fract;
 223
 224         clk_fd_get_div(hw, &fract);
 225
 226         *val = fract.numerator;
 227
 228         return 0;
 229 }
 230 DEFINE_DEBUGFS_ATTRIBUTE(clk_fd_numerator_fops, clk_fd_numerator_get, NULL, "%llu\n");
 231
 232 static int clk_fd_denominator_get(void *hw, u64 *val)
 233 {
 234         struct u32_fract fract;
 235
 236         clk_fd_get_div(hw, &fract);
 237
 238         *val = fract.denominator;
 239
 240         return 0;
 241 }
 242 DEFINE_DEBUGFS_ATTRIBUTE(clk_fd_denominator_fops, clk_fd_denominator_get, NULL, "%llu\n");
 243
 244 static void clk_fd_debug_init(struct clk_hw *hw, struct dentry *dentry)
 245 {
 246         debugfs_create_file("numerator", 0444, dentry, hw, &clk_fd_numerator_fops);
 247         debugfs_create_file("denominator", 0444, dentry, hw, &clk_fd_denominator_fops);
 248 }
 249 #endif
 250
 251 const struct clk_ops clk_fractional_divider_ops = {
 252         .recalc_rate = clk_fd_recalc_rate,
 253         .round_rate = clk_fd_round_rate,
 254         .set_rate = clk_fd_set_rate,
 255 #ifdef CONFIG_DEBUG_FS
 256         .debug_init = clk_fd_debug_init,
 257 #endif
 258 };
 259 EXPORT_SYMBOL_GPL(clk_fractional_divider_ops);
 260
 261 struct clk_hw *clk_hw_register_fractional_divider(struct device *dev,
 262                 const char *name, const char *parent_name, unsigned long flags,
 263                 void __iomem *reg, u8 mshift, u8 mwidth, u8 nshift, u8 nwidth,
 264                 u8 clk_divider_flags, spinlock_t *lock)
 265 {
 266         struct clk_fractional_divider *fd;
 267         struct clk_init_data init;
 268         struct clk_hw *hw;
 269         int ret;
 270
 271         fd = kzalloc(sizeof(*fd), GFP_KERNEL);
 272         if (!fd)
 273                 return ERR_PTR(-ENOMEM);
 274
 275         init.name = name;
 276         init.ops = &clk_fractional_divider_ops;
 277         init.flags = flags;
 278         init.parent_names = parent_name ? &parent_name : NULL;
 279         init.num_parents = parent_name ? 1 : 0;
 280
 281         fd->reg = reg;
 282         fd->mshift = mshift;
 283         fd->mwidth = mwidth;
 284         fd->nshift = nshift;
 285         fd->nwidth = nwidth;
 286         fd->flags = clk_divider_flags;
 287         fd->lock = lock;
 288         fd->hw.init = &init;
 289
 290         hw = &fd->hw;
 291         ret = clk_hw_register(dev, hw);
 292         if (ret) {
 293                 kfree(fd);
 294                 hw = ERR_PTR(ret);
 295         }
 296
 297         return hw;
 298 }
 299 EXPORT_SYMBOL_GPL(clk_hw_register_fractional_divider);
 300
 301 struct clk *clk_register_fractional_divider(struct device *dev,
 302                 const char *name, const char *parent_name, unsigned long flags,
 303                 void __iomem *reg, u8 mshift, u8 mwidth, u8 nshift, u8 nwidth,
 304                 u8 clk_divider_flags, spinlock_t *lock)
 305 {
 306         struct clk_hw *hw;
 307
 308         hw = clk_hw_register_fractional_divider(dev, name, parent_name, flags,
 309                         reg, mshift, mwidth, nshift, nwidth, clk_divider_flags,
 310                         lock);
 311         if (IS_ERR(hw))
 312                 return ERR_CAST(hw);
 313         return hw->clk;
 314 }
 315 EXPORT_SYMBOL_GPL(clk_register_fractional_divider);
 316
 317 void clk_hw_unregister_fractional_divider(struct clk_hw *hw)
 318 {
 319         struct clk_fractional_divider *fd;
 320
 321         fd = to_clk_fd(hw);
 322
 323         clk_hw_unregister(hw);
 324         kfree(fd);
 325 }