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
53static 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(addr: fd->reg);
59}
60
61static 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, addr: fd->reg);
67}
68
69static 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(lock: 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
104static 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: &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
120void 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(l: *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 = 1 << fd->mwidth;
144 max_n = 1 << 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(given_numerator: rate, given_denominator: *parent_rate, max_numerator: max_m, max_denominator: max_n, best_numerator: m, best_denominator: n);
151}
152EXPORT_SYMBOL_GPL(clk_fractional_divider_general_approximation);
153
154static 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
175static 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 = 1 << fd->mwidth;
186 max_n = 1 << 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(given_numerator: rate, given_denominator: parent_rate, max_numerator: max_m, max_denominator: max_n, best_numerator: &m, best_denominator: &n);
192
193 if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
194 m--;
195 n--;
196 }
197
198 if (fd->lock)
199 spin_lock_irqsave(fd->lock, flags);
200 else
201 __acquire(fd->lock);
202
203 mmask = GENMASK(fd->mwidth - 1, 0) << fd->mshift;
204 nmask = GENMASK(fd->nwidth - 1, 0) << fd->nshift;
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(lock: fd->lock, flags);
213 else
214 __release(fd->lock);
215
216 return 0;
217}
218
219#ifdef CONFIG_DEBUG_FS
220static int clk_fd_numerator_get(void *hw, u64 *val)
221{
222 struct u32_fract fract;
223
224 clk_fd_get_div(hw, fract: &fract);
225
226 *val = fract.numerator;
227
228 return 0;
229}
230DEFINE_DEBUGFS_ATTRIBUTE(clk_fd_numerator_fops, clk_fd_numerator_get, NULL, "%llu\n");
231
232static int clk_fd_denominator_get(void *hw, u64 *val)
233{
234 struct u32_fract fract;
235
236 clk_fd_get_div(hw, fract: &fract);
237
238 *val = fract.denominator;
239
240 return 0;
241}
242DEFINE_DEBUGFS_ATTRIBUTE(clk_fd_denominator_fops, clk_fd_denominator_get, NULL, "%llu\n");
243
244static void clk_fd_debug_init(struct clk_hw *hw, struct dentry *dentry)
245{
246 debugfs_create_file(name: "numerator", mode: 0444, parent: dentry, data: hw, fops: &clk_fd_numerator_fops);
247 debugfs_create_file(name: "denominator", mode: 0444, parent: dentry, data: hw, fops: &clk_fd_denominator_fops);
248}
249#endif
250
251const 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};
259EXPORT_SYMBOL_GPL(clk_fractional_divider_ops);
260
261struct 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(size: sizeof(*fd), GFP_KERNEL);
272 if (!fd)
273 return ERR_PTR(error: -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(objp: fd);
294 hw = ERR_PTR(error: ret);
295 }
296
297 return hw;
298}
299EXPORT_SYMBOL_GPL(clk_hw_register_fractional_divider);
300
301struct 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(ptr: hw))
312 return ERR_CAST(ptr: hw);
313 return hw->clk;
314}
315EXPORT_SYMBOL_GPL(clk_register_fractional_divider);
316
317void 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(objp: fd);
325}
326

source code of linux/drivers/clk/clk-fractional-divider.c