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(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, 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(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);
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
127	/*
128	 * Get rate closer to *parent_rate to guarantee there is no overflow
129	 * for m and n. In the result it will be the nearest rate left shifted
130	 * by (scale - fd->nwidth) bits.
131	 *
132	 * For the detailed explanation see the top comment in this file.
133	 */
134	if (fd->flags & CLK_FRAC_DIVIDER_POWER_OF_TWO_PS) {
135		unsigned long scale = fls_long(*parent_rate / rate - 1);
136
137		if (scale > fd->nwidth)
138			rate <<= scale - fd->nwidth;
139	}
140
141	rational_best_approximation(rate, *parent_rate,
142			GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
143			m, n);
144}
145
146static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
147			      unsigned long *parent_rate)
148{
149	struct clk_fractional_divider *fd = to_clk_fd(hw);
150	unsigned long m, n;
151	u64 ret;
152
153	if (!rate || (!clk_hw_can_set_rate_parent(hw) && rate >= *parent_rate))
154		return *parent_rate;
155
156	if (fd->approximation)
157		fd->approximation(hw, rate, parent_rate, &m, &n);
158	else
159		clk_fractional_divider_general_approximation(hw, rate, parent_rate, &m, &n);
160
161	ret = (u64)*parent_rate * m;
162	do_div(ret, n);
163
164	return ret;
165}
166
167static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
168			   unsigned long parent_rate)
169{
170	struct clk_fractional_divider *fd = to_clk_fd(hw);
171	unsigned long flags = 0;
172	unsigned long m, n;
173	u32 mmask, nmask;
174	u32 val;
175
176	rational_best_approximation(rate, parent_rate,
177			GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
178			&m, &n);
179
180	if (fd->flags & CLK_FRAC_DIVIDER_ZERO_BASED) {
181		m--;
182		n--;
183	}
184
185	if (fd->lock)
186		spin_lock_irqsave(fd->lock, flags);
187	else
188		__acquire(fd->lock);
189
190	mmask = GENMASK(fd->mwidth - 1, 0) << fd->mshift;
191	nmask = GENMASK(fd->nwidth - 1, 0) << fd->nshift;
192
193	val = clk_fd_readl(fd);
194	val &= ~(mmask | nmask);
195	val |= (m << fd->mshift) | (n << fd->nshift);
196	clk_fd_writel(fd, val);
197
198	if (fd->lock)
199		spin_unlock_irqrestore(fd->lock, flags);
200	else
201		__release(fd->lock);
202
203	return 0;
204}
205
206#ifdef CONFIG_DEBUG_FS
207static int clk_fd_numerator_get(void *hw, u64 *val)
208{
209	struct u32_fract fract;
210
211	clk_fd_get_div(hw, &fract);
212
213	*val = fract.numerator;
214
215	return 0;
216}
217DEFINE_DEBUGFS_ATTRIBUTE(clk_fd_numerator_fops, clk_fd_numerator_get, NULL, "%llu\n");
218
219static int clk_fd_denominator_get(void *hw, u64 *val)
220{
221	struct u32_fract fract;
222
223	clk_fd_get_div(hw, &fract);
224
225	*val = fract.denominator;
226
227	return 0;
228}
229DEFINE_DEBUGFS_ATTRIBUTE(clk_fd_denominator_fops, clk_fd_denominator_get, NULL, "%llu\n");
230
231static void clk_fd_debug_init(struct clk_hw *hw, struct dentry *dentry)
232{
233	debugfs_create_file("numerator", 0444, dentry, hw, &clk_fd_numerator_fops);
234	debugfs_create_file("denominator", 0444, dentry, hw, &clk_fd_denominator_fops);
235}
236#endif
237
238const struct clk_ops clk_fractional_divider_ops = {
239	.recalc_rate = clk_fd_recalc_rate,
240	.round_rate = clk_fd_round_rate,
241	.set_rate = clk_fd_set_rate,
242#ifdef CONFIG_DEBUG_FS
243	.debug_init = clk_fd_debug_init,
244#endif
245};
246EXPORT_SYMBOL_GPL(clk_fractional_divider_ops);
247
248struct clk_hw *clk_hw_register_fractional_divider(struct device *dev,
249		const char *name, const char *parent_name, unsigned long flags,
250		void __iomem *reg, u8 mshift, u8 mwidth, u8 nshift, u8 nwidth,
251		u8 clk_divider_flags, spinlock_t *lock)
252{
253	struct clk_fractional_divider *fd;
254	struct clk_init_data init;
255	struct clk_hw *hw;
256	int ret;
257
258	fd = kzalloc(sizeof(*fd), GFP_KERNEL);
259	if (!fd)
260		return ERR_PTR(-ENOMEM);
261
262	init.name = name;
263	init.ops = &clk_fractional_divider_ops;
264	init.flags = flags;
265	init.parent_names = parent_name ? &parent_name : NULL;
266	init.num_parents = parent_name ? 1 : 0;
267
268	fd->reg = reg;
269	fd->mshift = mshift;
270	fd->mwidth = mwidth;
271	fd->nshift = nshift;
272	fd->nwidth = nwidth;
273	fd->flags = clk_divider_flags;
274	fd->lock = lock;
275	fd->hw.init = &init;
276
277	hw = &fd->hw;
278	ret = clk_hw_register(dev, hw);
279	if (ret) {
280		kfree(fd);
281		hw = ERR_PTR(ret);
282	}
283
284	return hw;
285}
286EXPORT_SYMBOL_GPL(clk_hw_register_fractional_divider);
287
288struct clk *clk_register_fractional_divider(struct device *dev,
289		const char *name, const char *parent_name, unsigned long flags,
290		void __iomem *reg, u8 mshift, u8 mwidth, u8 nshift, u8 nwidth,
291		u8 clk_divider_flags, spinlock_t *lock)
292{
293	struct clk_hw *hw;
294
295	hw = clk_hw_register_fractional_divider(dev, name, parent_name, flags,
296			reg, mshift, mwidth, nshift, nwidth, clk_divider_flags,
297			lock);
298	if (IS_ERR(hw))
299		return ERR_CAST(hw);
300	return hw->clk;
301}
302EXPORT_SYMBOL_GPL(clk_register_fractional_divider);
303
304void clk_hw_unregister_fractional_divider(struct clk_hw *hw)
305{
306	struct clk_fractional_divider *fd;
307
308	fd = to_clk_fd(hw);
309
310	clk_hw_unregister(hw);
311	kfree(fd);
312}
313