xref: /openbmc/linux/drivers/clk/clk-apple-nco.c (revision 236541ac)
1 // SPDX-License-Identifier: GPL-2.0-only OR MIT
2 /*
3  * Driver for an SoC block (Numerically Controlled Oscillator)
4  * found on t8103 (M1) and other Apple chips
5  *
6  * Copyright (C) The Asahi Linux Contributors
7  */
8 
9 #include <linux/bits.h>
10 #include <linux/bitfield.h>
11 #include <linux/clk-provider.h>
12 #include <linux/io.h>
13 #include <linux/kernel.h>
14 #include <linux/math64.h>
15 #include <linux/module.h>
16 #include <linux/of.h>
17 #include <linux/platform_device.h>
18 #include <linux/spinlock.h>
19 
20 #define NCO_CHANNEL_STRIDE	0x4000
21 #define NCO_CHANNEL_REGSIZE	20
22 
23 #define REG_CTRL	0
24 #define CTRL_ENABLE	BIT(31)
25 #define REG_DIV		4
26 #define DIV_FINE	GENMASK(1, 0)
27 #define DIV_COARSE	GENMASK(12, 2)
28 #define REG_INC1	8
29 #define REG_INC2	12
30 #define REG_ACCINIT	16
31 
32 /*
33  * Theory of operation (postulated)
34  *
35  * The REG_DIV register indirectly expresses a base integer divisor, roughly
36  * corresponding to twice the desired ratio of input to output clock. This
37  * base divisor is adjusted on a cycle-by-cycle basis based on the state of a
38  * 32-bit phase accumulator to achieve a desired precise clock ratio over the
39  * long term.
40  *
41  * Specifically an output clock cycle is produced after (REG_DIV divisor)/2
42  * or (REG_DIV divisor + 1)/2 input cycles, the latter taking effect when top
43  * bit of the 32-bit accumulator is set. The accumulator is incremented each
44  * produced output cycle, by the value from either REG_INC1 or REG_INC2, which
45  * of the two is selected depending again on the accumulator's current top bit.
46  *
47  * Because the NCO hardware implements counting of input clock cycles in part
48  * in a Galois linear-feedback shift register, the higher bits of divisor
49  * are programmed into REG_DIV by picking an appropriate LFSR state. See
50  * applnco_compute_tables/applnco_div_translate for details on this.
51  */
52 
53 #define LFSR_POLY	0xa01
54 #define LFSR_INIT	0x7ff
55 #define LFSR_LEN	11
56 #define LFSR_PERIOD	((1 << LFSR_LEN) - 1)
57 #define LFSR_TBLSIZE	(1 << LFSR_LEN)
58 
59 /* The minimal attainable coarse divisor (first value in table) */
60 #define COARSE_DIV_OFFSET 2
61 
62 struct applnco_tables {
63 	u16 fwd[LFSR_TBLSIZE];
64 	u16 inv[LFSR_TBLSIZE];
65 };
66 
67 struct applnco_channel {
68 	void __iomem *base;
69 	struct applnco_tables *tbl;
70 	struct clk_hw hw;
71 
72 	spinlock_t lock;
73 };
74 
75 #define to_applnco_channel(_hw) container_of(_hw, struct applnco_channel, hw)
76 
applnco_enable_nolock(struct clk_hw * hw)77 static void applnco_enable_nolock(struct clk_hw *hw)
78 {
79 	struct applnco_channel *chan = to_applnco_channel(hw);
80 	u32 val;
81 
82 	val = readl_relaxed(chan->base + REG_CTRL);
83 	writel_relaxed(val | CTRL_ENABLE, chan->base + REG_CTRL);
84 }
85 
applnco_disable_nolock(struct clk_hw * hw)86 static void applnco_disable_nolock(struct clk_hw *hw)
87 {
88 	struct applnco_channel *chan = to_applnco_channel(hw);
89 	u32 val;
90 
91 	val = readl_relaxed(chan->base + REG_CTRL);
92 	writel_relaxed(val & ~CTRL_ENABLE, chan->base + REG_CTRL);
93 }
94 
applnco_is_enabled(struct clk_hw * hw)95 static int applnco_is_enabled(struct clk_hw *hw)
96 {
97 	struct applnco_channel *chan = to_applnco_channel(hw);
98 
99 	return (readl_relaxed(chan->base + REG_CTRL) & CTRL_ENABLE) != 0;
100 }
101 
applnco_compute_tables(struct applnco_tables * tbl)102 static void applnco_compute_tables(struct applnco_tables *tbl)
103 {
104 	int i;
105 	u32 state = LFSR_INIT;
106 
107 	/*
108 	 * Go through the states of a Galois LFSR and build
109 	 * a coarse divisor translation table.
110 	 */
111 	for (i = LFSR_PERIOD; i > 0; i--) {
112 		if (state & 1)
113 			state = (state >> 1) ^ (LFSR_POLY >> 1);
114 		else
115 			state = (state >> 1);
116 		tbl->fwd[i] = state;
117 		tbl->inv[state] = i;
118 	}
119 
120 	/* Zero value is special-cased */
121 	tbl->fwd[0] = 0;
122 	tbl->inv[0] = 0;
123 }
124 
applnco_div_out_of_range(unsigned int div)125 static bool applnco_div_out_of_range(unsigned int div)
126 {
127 	unsigned int coarse = div / 4;
128 
129 	return coarse < COARSE_DIV_OFFSET ||
130 		coarse >= COARSE_DIV_OFFSET + LFSR_TBLSIZE;
131 }
132 
applnco_div_translate(struct applnco_tables * tbl,unsigned int div)133 static u32 applnco_div_translate(struct applnco_tables *tbl, unsigned int div)
134 {
135 	unsigned int coarse = div / 4;
136 
137 	if (WARN_ON(applnco_div_out_of_range(div)))
138 		return 0;
139 
140 	return FIELD_PREP(DIV_COARSE, tbl->fwd[coarse - COARSE_DIV_OFFSET]) |
141 			FIELD_PREP(DIV_FINE, div % 4);
142 }
143 
applnco_div_translate_inv(struct applnco_tables * tbl,u32 regval)144 static unsigned int applnco_div_translate_inv(struct applnco_tables *tbl, u32 regval)
145 {
146 	unsigned int coarse, fine;
147 
148 	coarse = tbl->inv[FIELD_GET(DIV_COARSE, regval)] + COARSE_DIV_OFFSET;
149 	fine = FIELD_GET(DIV_FINE, regval);
150 
151 	return coarse * 4 + fine;
152 }
153 
applnco_set_rate(struct clk_hw * hw,unsigned long rate,unsigned long parent_rate)154 static int applnco_set_rate(struct clk_hw *hw, unsigned long rate,
155 				unsigned long parent_rate)
156 {
157 	struct applnco_channel *chan = to_applnco_channel(hw);
158 	unsigned long flags;
159 	u32 div, inc1, inc2;
160 	bool was_enabled;
161 
162 	div = 2 * parent_rate / rate;
163 	inc1 = 2 * parent_rate - div * rate;
164 	inc2 = inc1 - rate;
165 
166 	if (applnco_div_out_of_range(div))
167 		return -EINVAL;
168 
169 	div = applnco_div_translate(chan->tbl, div);
170 
171 	spin_lock_irqsave(&chan->lock, flags);
172 	was_enabled = applnco_is_enabled(hw);
173 	applnco_disable_nolock(hw);
174 
175 	writel_relaxed(div,  chan->base + REG_DIV);
176 	writel_relaxed(inc1, chan->base + REG_INC1);
177 	writel_relaxed(inc2, chan->base + REG_INC2);
178 
179 	/* Presumably a neutral initial value for accumulator */
180 	writel_relaxed(1 << 31, chan->base + REG_ACCINIT);
181 
182 	if (was_enabled)
183 		applnco_enable_nolock(hw);
184 	spin_unlock_irqrestore(&chan->lock, flags);
185 
186 	return 0;
187 }
188 
applnco_recalc_rate(struct clk_hw * hw,unsigned long parent_rate)189 static unsigned long applnco_recalc_rate(struct clk_hw *hw,
190 				unsigned long parent_rate)
191 {
192 	struct applnco_channel *chan = to_applnco_channel(hw);
193 	u32 div, inc1, inc2, incbase;
194 
195 	div = applnco_div_translate_inv(chan->tbl,
196 			readl_relaxed(chan->base + REG_DIV));
197 
198 	inc1 = readl_relaxed(chan->base + REG_INC1);
199 	inc2 = readl_relaxed(chan->base + REG_INC2);
200 
201 	/*
202 	 * We don't support wraparound of accumulator
203 	 * nor the edge case of both increments being zero
204 	 */
205 	if (inc1 >= (1 << 31) || inc2 < (1 << 31) || (inc1 == 0 && inc2 == 0))
206 		return 0;
207 
208 	/* Scale both sides of division by incbase to maintain precision */
209 	incbase = inc1 - inc2;
210 
211 	return div64_u64(((u64) parent_rate) * 2 * incbase,
212 			((u64) div) * incbase + inc1);
213 }
214 
applnco_round_rate(struct clk_hw * hw,unsigned long rate,unsigned long * parent_rate)215 static long applnco_round_rate(struct clk_hw *hw, unsigned long rate,
216 				unsigned long *parent_rate)
217 {
218 	unsigned long lo = *parent_rate / (COARSE_DIV_OFFSET + LFSR_TBLSIZE) + 1;
219 	unsigned long hi = *parent_rate / COARSE_DIV_OFFSET;
220 
221 	return clamp(rate, lo, hi);
222 }
223 
applnco_enable(struct clk_hw * hw)224 static int applnco_enable(struct clk_hw *hw)
225 {
226 	struct applnco_channel *chan = to_applnco_channel(hw);
227 	unsigned long flags;
228 
229 	spin_lock_irqsave(&chan->lock, flags);
230 	applnco_enable_nolock(hw);
231 	spin_unlock_irqrestore(&chan->lock, flags);
232 
233 	return 0;
234 }
235 
applnco_disable(struct clk_hw * hw)236 static void applnco_disable(struct clk_hw *hw)
237 {
238 	struct applnco_channel *chan = to_applnco_channel(hw);
239 	unsigned long flags;
240 
241 	spin_lock_irqsave(&chan->lock, flags);
242 	applnco_disable_nolock(hw);
243 	spin_unlock_irqrestore(&chan->lock, flags);
244 }
245 
246 static const struct clk_ops applnco_ops = {
247 	.set_rate = applnco_set_rate,
248 	.recalc_rate = applnco_recalc_rate,
249 	.round_rate = applnco_round_rate,
250 	.enable = applnco_enable,
251 	.disable = applnco_disable,
252 	.is_enabled = applnco_is_enabled,
253 };
254 
applnco_probe(struct platform_device * pdev)255 static int applnco_probe(struct platform_device *pdev)
256 {
257 	struct device_node *np = pdev->dev.of_node;
258 	struct clk_parent_data pdata = { .index = 0 };
259 	struct clk_init_data init;
260 	struct clk_hw_onecell_data *onecell_data;
261 	void __iomem *base;
262 	struct resource *res;
263 	struct applnco_tables *tbl;
264 	unsigned int nchannels;
265 	int ret, i;
266 
267 	base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
268 	if (IS_ERR(base))
269 		return PTR_ERR(base);
270 
271 	if (resource_size(res) < NCO_CHANNEL_REGSIZE)
272 		return -EINVAL;
273 	nchannels = (resource_size(res) - NCO_CHANNEL_REGSIZE)
274 			/ NCO_CHANNEL_STRIDE + 1;
275 
276 	onecell_data = devm_kzalloc(&pdev->dev, struct_size(onecell_data, hws,
277 							nchannels), GFP_KERNEL);
278 	if (!onecell_data)
279 		return -ENOMEM;
280 	onecell_data->num = nchannels;
281 
282 	tbl = devm_kzalloc(&pdev->dev, sizeof(*tbl), GFP_KERNEL);
283 	if (!tbl)
284 		return -ENOMEM;
285 	applnco_compute_tables(tbl);
286 
287 	for (i = 0; i < nchannels; i++) {
288 		struct applnco_channel *chan;
289 
290 		chan = devm_kzalloc(&pdev->dev, sizeof(*chan), GFP_KERNEL);
291 		if (!chan)
292 			return -ENOMEM;
293 		chan->base = base + NCO_CHANNEL_STRIDE * i;
294 		chan->tbl = tbl;
295 		spin_lock_init(&chan->lock);
296 
297 		memset(&init, 0, sizeof(init));
298 		init.name = devm_kasprintf(&pdev->dev, GFP_KERNEL,
299 						"%s-%d", np->name, i);
300 		init.ops = &applnco_ops;
301 		init.parent_data = &pdata;
302 		init.num_parents = 1;
303 		init.flags = 0;
304 
305 		chan->hw.init = &init;
306 		ret = devm_clk_hw_register(&pdev->dev, &chan->hw);
307 		if (ret)
308 			return ret;
309 
310 		onecell_data->hws[i] = &chan->hw;
311 	}
312 
313 	return devm_of_clk_add_hw_provider(&pdev->dev, of_clk_hw_onecell_get,
314 							onecell_data);
315 }
316 
317 static const struct of_device_id applnco_ids[] = {
318 	{ .compatible = "apple,nco" },
319 	{ }
320 };
321 MODULE_DEVICE_TABLE(of, applnco_ids);
322 
323 static struct platform_driver applnco_driver = {
324 	.driver = {
325 		.name = "apple-nco",
326 		.of_match_table = applnco_ids,
327 	},
328 	.probe = applnco_probe,
329 };
330 module_platform_driver(applnco_driver);
331 
332 MODULE_AUTHOR("Martin Povišer <povik+lin@cutebit.org>");
333 MODULE_DESCRIPTION("Clock driver for NCO blocks on Apple SoCs");
334 MODULE_LICENSE("GPL");
335