xref: /linux/arch/mips/ath79/clock.c (revision 42249094f79422fbf5ed4b54eeb48ff096809b8f)
1 /*
2  *  Atheros AR71XX/AR724X/AR913X common routines
3  *
4  *  Copyright (C) 2010-2011 Jaiganesh Narayanan <jnarayanan@atheros.com>
5  *  Copyright (C) 2011 Gabor Juhos <juhosg@openwrt.org>
6  *
7  *  Parts of this file are based on Atheros' 2.6.15/2.6.31 BSP
8  *
9  *  This program is free software; you can redistribute it and/or modify it
10  *  under the terms of the GNU General Public License version 2 as published
11  *  by the Free Software Foundation.
12  */
13 
14 #include <linux/kernel.h>
15 #include <linux/module.h>
16 #include <linux/init.h>
17 #include <linux/err.h>
18 #include <linux/clk.h>
19 #include <linux/clkdev.h>
20 
21 #include <asm/div64.h>
22 
23 #include <asm/mach-ath79/ath79.h>
24 #include <asm/mach-ath79/ar71xx_regs.h>
25 #include "common.h"
26 
27 #define AR71XX_BASE_FREQ	40000000
28 #define AR724X_BASE_FREQ	5000000
29 #define AR913X_BASE_FREQ	5000000
30 
31 struct clk {
32 	unsigned long rate;
33 };
34 
35 static void __init ath79_add_sys_clkdev(const char *id, unsigned long rate)
36 {
37 	struct clk *clk;
38 	int err;
39 
40 	clk = kzalloc(sizeof(*clk), GFP_KERNEL);
41 	if (!clk)
42 		panic("failed to allocate %s clock structure", id);
43 
44 	clk->rate = rate;
45 
46 	err = clk_register_clkdev(clk, id, NULL);
47 	if (err)
48 		panic("unable to register %s clock device", id);
49 }
50 
51 static void __init ar71xx_clocks_init(void)
52 {
53 	unsigned long ref_rate;
54 	unsigned long cpu_rate;
55 	unsigned long ddr_rate;
56 	unsigned long ahb_rate;
57 	u32 pll;
58 	u32 freq;
59 	u32 div;
60 
61 	ref_rate = AR71XX_BASE_FREQ;
62 
63 	pll = ath79_pll_rr(AR71XX_PLL_REG_CPU_CONFIG);
64 
65 	div = ((pll >> AR71XX_PLL_DIV_SHIFT) & AR71XX_PLL_DIV_MASK) + 1;
66 	freq = div * ref_rate;
67 
68 	div = ((pll >> AR71XX_CPU_DIV_SHIFT) & AR71XX_CPU_DIV_MASK) + 1;
69 	cpu_rate = freq / div;
70 
71 	div = ((pll >> AR71XX_DDR_DIV_SHIFT) & AR71XX_DDR_DIV_MASK) + 1;
72 	ddr_rate = freq / div;
73 
74 	div = (((pll >> AR71XX_AHB_DIV_SHIFT) & AR71XX_AHB_DIV_MASK) + 1) * 2;
75 	ahb_rate = cpu_rate / div;
76 
77 	ath79_add_sys_clkdev("ref", ref_rate);
78 	ath79_add_sys_clkdev("cpu", cpu_rate);
79 	ath79_add_sys_clkdev("ddr", ddr_rate);
80 	ath79_add_sys_clkdev("ahb", ahb_rate);
81 
82 	clk_add_alias("wdt", NULL, "ahb", NULL);
83 	clk_add_alias("uart", NULL, "ahb", NULL);
84 }
85 
86 static void __init ar724x_clocks_init(void)
87 {
88 	unsigned long ref_rate;
89 	unsigned long cpu_rate;
90 	unsigned long ddr_rate;
91 	unsigned long ahb_rate;
92 	u32 pll;
93 	u32 freq;
94 	u32 div;
95 
96 	ref_rate = AR724X_BASE_FREQ;
97 	pll = ath79_pll_rr(AR724X_PLL_REG_CPU_CONFIG);
98 
99 	div = ((pll >> AR724X_PLL_DIV_SHIFT) & AR724X_PLL_DIV_MASK);
100 	freq = div * ref_rate;
101 
102 	div = ((pll >> AR724X_PLL_REF_DIV_SHIFT) & AR724X_PLL_REF_DIV_MASK);
103 	freq *= div;
104 
105 	cpu_rate = freq;
106 
107 	div = ((pll >> AR724X_DDR_DIV_SHIFT) & AR724X_DDR_DIV_MASK) + 1;
108 	ddr_rate = freq / div;
109 
110 	div = (((pll >> AR724X_AHB_DIV_SHIFT) & AR724X_AHB_DIV_MASK) + 1) * 2;
111 	ahb_rate = cpu_rate / div;
112 
113 	ath79_add_sys_clkdev("ref", ref_rate);
114 	ath79_add_sys_clkdev("cpu", cpu_rate);
115 	ath79_add_sys_clkdev("ddr", ddr_rate);
116 	ath79_add_sys_clkdev("ahb", ahb_rate);
117 
118 	clk_add_alias("wdt", NULL, "ahb", NULL);
119 	clk_add_alias("uart", NULL, "ahb", NULL);
120 }
121 
122 static void __init ar913x_clocks_init(void)
123 {
124 	unsigned long ref_rate;
125 	unsigned long cpu_rate;
126 	unsigned long ddr_rate;
127 	unsigned long ahb_rate;
128 	u32 pll;
129 	u32 freq;
130 	u32 div;
131 
132 	ref_rate = AR913X_BASE_FREQ;
133 	pll = ath79_pll_rr(AR913X_PLL_REG_CPU_CONFIG);
134 
135 	div = ((pll >> AR913X_PLL_DIV_SHIFT) & AR913X_PLL_DIV_MASK);
136 	freq = div * ref_rate;
137 
138 	cpu_rate = freq;
139 
140 	div = ((pll >> AR913X_DDR_DIV_SHIFT) & AR913X_DDR_DIV_MASK) + 1;
141 	ddr_rate = freq / div;
142 
143 	div = (((pll >> AR913X_AHB_DIV_SHIFT) & AR913X_AHB_DIV_MASK) + 1) * 2;
144 	ahb_rate = cpu_rate / div;
145 
146 	ath79_add_sys_clkdev("ref", ref_rate);
147 	ath79_add_sys_clkdev("cpu", cpu_rate);
148 	ath79_add_sys_clkdev("ddr", ddr_rate);
149 	ath79_add_sys_clkdev("ahb", ahb_rate);
150 
151 	clk_add_alias("wdt", NULL, "ahb", NULL);
152 	clk_add_alias("uart", NULL, "ahb", NULL);
153 }
154 
155 static void __init ar933x_clocks_init(void)
156 {
157 	unsigned long ref_rate;
158 	unsigned long cpu_rate;
159 	unsigned long ddr_rate;
160 	unsigned long ahb_rate;
161 	u32 clock_ctrl;
162 	u32 cpu_config;
163 	u32 freq;
164 	u32 t;
165 
166 	t = ath79_reset_rr(AR933X_RESET_REG_BOOTSTRAP);
167 	if (t & AR933X_BOOTSTRAP_REF_CLK_40)
168 		ref_rate = (40 * 1000 * 1000);
169 	else
170 		ref_rate = (25 * 1000 * 1000);
171 
172 	clock_ctrl = ath79_pll_rr(AR933X_PLL_CLOCK_CTRL_REG);
173 	if (clock_ctrl & AR933X_PLL_CLOCK_CTRL_BYPASS) {
174 		cpu_rate = ref_rate;
175 		ahb_rate = ref_rate;
176 		ddr_rate = ref_rate;
177 	} else {
178 		cpu_config = ath79_pll_rr(AR933X_PLL_CPU_CONFIG_REG);
179 
180 		t = (cpu_config >> AR933X_PLL_CPU_CONFIG_REFDIV_SHIFT) &
181 		    AR933X_PLL_CPU_CONFIG_REFDIV_MASK;
182 		freq = ref_rate / t;
183 
184 		t = (cpu_config >> AR933X_PLL_CPU_CONFIG_NINT_SHIFT) &
185 		    AR933X_PLL_CPU_CONFIG_NINT_MASK;
186 		freq *= t;
187 
188 		t = (cpu_config >> AR933X_PLL_CPU_CONFIG_OUTDIV_SHIFT) &
189 		    AR933X_PLL_CPU_CONFIG_OUTDIV_MASK;
190 		if (t == 0)
191 			t = 1;
192 
193 		freq >>= t;
194 
195 		t = ((clock_ctrl >> AR933X_PLL_CLOCK_CTRL_CPU_DIV_SHIFT) &
196 		     AR933X_PLL_CLOCK_CTRL_CPU_DIV_MASK) + 1;
197 		cpu_rate = freq / t;
198 
199 		t = ((clock_ctrl >> AR933X_PLL_CLOCK_CTRL_DDR_DIV_SHIFT) &
200 		      AR933X_PLL_CLOCK_CTRL_DDR_DIV_MASK) + 1;
201 		ddr_rate = freq / t;
202 
203 		t = ((clock_ctrl >> AR933X_PLL_CLOCK_CTRL_AHB_DIV_SHIFT) &
204 		     AR933X_PLL_CLOCK_CTRL_AHB_DIV_MASK) + 1;
205 		ahb_rate = freq / t;
206 	}
207 
208 	ath79_add_sys_clkdev("ref", ref_rate);
209 	ath79_add_sys_clkdev("cpu", cpu_rate);
210 	ath79_add_sys_clkdev("ddr", ddr_rate);
211 	ath79_add_sys_clkdev("ahb", ahb_rate);
212 
213 	clk_add_alias("wdt", NULL, "ahb", NULL);
214 	clk_add_alias("uart", NULL, "ref", NULL);
215 }
216 
217 static u32 __init ar934x_get_pll_freq(u32 ref, u32 ref_div, u32 nint, u32 nfrac,
218 				      u32 frac, u32 out_div)
219 {
220 	u64 t;
221 	u32 ret;
222 
223 	t = ref;
224 	t *= nint;
225 	do_div(t, ref_div);
226 	ret = t;
227 
228 	t = ref;
229 	t *= nfrac;
230 	do_div(t, ref_div * frac);
231 	ret += t;
232 
233 	ret /= (1 << out_div);
234 	return ret;
235 }
236 
237 static void __init ar934x_clocks_init(void)
238 {
239 	unsigned long ref_rate;
240 	unsigned long cpu_rate;
241 	unsigned long ddr_rate;
242 	unsigned long ahb_rate;
243 	u32 pll, out_div, ref_div, nint, nfrac, frac, clk_ctrl, postdiv;
244 	u32 cpu_pll, ddr_pll;
245 	u32 bootstrap;
246 	void __iomem *dpll_base;
247 
248 	dpll_base = ioremap(AR934X_SRIF_BASE, AR934X_SRIF_SIZE);
249 
250 	bootstrap = ath79_reset_rr(AR934X_RESET_REG_BOOTSTRAP);
251 	if (bootstrap & AR934X_BOOTSTRAP_REF_CLK_40)
252 		ref_rate = 40 * 1000 * 1000;
253 	else
254 		ref_rate = 25 * 1000 * 1000;
255 
256 	pll = __raw_readl(dpll_base + AR934X_SRIF_CPU_DPLL2_REG);
257 	if (pll & AR934X_SRIF_DPLL2_LOCAL_PLL) {
258 		out_div = (pll >> AR934X_SRIF_DPLL2_OUTDIV_SHIFT) &
259 			  AR934X_SRIF_DPLL2_OUTDIV_MASK;
260 		pll = __raw_readl(dpll_base + AR934X_SRIF_CPU_DPLL1_REG);
261 		nint = (pll >> AR934X_SRIF_DPLL1_NINT_SHIFT) &
262 		       AR934X_SRIF_DPLL1_NINT_MASK;
263 		nfrac = pll & AR934X_SRIF_DPLL1_NFRAC_MASK;
264 		ref_div = (pll >> AR934X_SRIF_DPLL1_REFDIV_SHIFT) &
265 			  AR934X_SRIF_DPLL1_REFDIV_MASK;
266 		frac = 1 << 18;
267 	} else {
268 		pll = ath79_pll_rr(AR934X_PLL_CPU_CONFIG_REG);
269 		out_div = (pll >> AR934X_PLL_CPU_CONFIG_OUTDIV_SHIFT) &
270 			AR934X_PLL_CPU_CONFIG_OUTDIV_MASK;
271 		ref_div = (pll >> AR934X_PLL_CPU_CONFIG_REFDIV_SHIFT) &
272 			  AR934X_PLL_CPU_CONFIG_REFDIV_MASK;
273 		nint = (pll >> AR934X_PLL_CPU_CONFIG_NINT_SHIFT) &
274 		       AR934X_PLL_CPU_CONFIG_NINT_MASK;
275 		nfrac = (pll >> AR934X_PLL_CPU_CONFIG_NFRAC_SHIFT) &
276 			AR934X_PLL_CPU_CONFIG_NFRAC_MASK;
277 		frac = 1 << 6;
278 	}
279 
280 	cpu_pll = ar934x_get_pll_freq(ref_rate, ref_div, nint,
281 				      nfrac, frac, out_div);
282 
283 	pll = __raw_readl(dpll_base + AR934X_SRIF_DDR_DPLL2_REG);
284 	if (pll & AR934X_SRIF_DPLL2_LOCAL_PLL) {
285 		out_div = (pll >> AR934X_SRIF_DPLL2_OUTDIV_SHIFT) &
286 			  AR934X_SRIF_DPLL2_OUTDIV_MASK;
287 		pll = __raw_readl(dpll_base + AR934X_SRIF_DDR_DPLL1_REG);
288 		nint = (pll >> AR934X_SRIF_DPLL1_NINT_SHIFT) &
289 		       AR934X_SRIF_DPLL1_NINT_MASK;
290 		nfrac = pll & AR934X_SRIF_DPLL1_NFRAC_MASK;
291 		ref_div = (pll >> AR934X_SRIF_DPLL1_REFDIV_SHIFT) &
292 			  AR934X_SRIF_DPLL1_REFDIV_MASK;
293 		frac = 1 << 18;
294 	} else {
295 		pll = ath79_pll_rr(AR934X_PLL_DDR_CONFIG_REG);
296 		out_div = (pll >> AR934X_PLL_DDR_CONFIG_OUTDIV_SHIFT) &
297 			  AR934X_PLL_DDR_CONFIG_OUTDIV_MASK;
298 		ref_div = (pll >> AR934X_PLL_DDR_CONFIG_REFDIV_SHIFT) &
299 			   AR934X_PLL_DDR_CONFIG_REFDIV_MASK;
300 		nint = (pll >> AR934X_PLL_DDR_CONFIG_NINT_SHIFT) &
301 		       AR934X_PLL_DDR_CONFIG_NINT_MASK;
302 		nfrac = (pll >> AR934X_PLL_DDR_CONFIG_NFRAC_SHIFT) &
303 			AR934X_PLL_DDR_CONFIG_NFRAC_MASK;
304 		frac = 1 << 10;
305 	}
306 
307 	ddr_pll = ar934x_get_pll_freq(ref_rate, ref_div, nint,
308 				      nfrac, frac, out_div);
309 
310 	clk_ctrl = ath79_pll_rr(AR934X_PLL_CPU_DDR_CLK_CTRL_REG);
311 
312 	postdiv = (clk_ctrl >> AR934X_PLL_CPU_DDR_CLK_CTRL_CPU_POST_DIV_SHIFT) &
313 		  AR934X_PLL_CPU_DDR_CLK_CTRL_CPU_POST_DIV_MASK;
314 
315 	if (clk_ctrl & AR934X_PLL_CPU_DDR_CLK_CTRL_CPU_PLL_BYPASS)
316 		cpu_rate = ref_rate;
317 	else if (clk_ctrl & AR934X_PLL_CPU_DDR_CLK_CTRL_CPUCLK_FROM_CPUPLL)
318 		cpu_rate = cpu_pll / (postdiv + 1);
319 	else
320 		cpu_rate = ddr_pll / (postdiv + 1);
321 
322 	postdiv = (clk_ctrl >> AR934X_PLL_CPU_DDR_CLK_CTRL_DDR_POST_DIV_SHIFT) &
323 		  AR934X_PLL_CPU_DDR_CLK_CTRL_DDR_POST_DIV_MASK;
324 
325 	if (clk_ctrl & AR934X_PLL_CPU_DDR_CLK_CTRL_DDR_PLL_BYPASS)
326 		ddr_rate = ref_rate;
327 	else if (clk_ctrl & AR934X_PLL_CPU_DDR_CLK_CTRL_DDRCLK_FROM_DDRPLL)
328 		ddr_rate = ddr_pll / (postdiv + 1);
329 	else
330 		ddr_rate = cpu_pll / (postdiv + 1);
331 
332 	postdiv = (clk_ctrl >> AR934X_PLL_CPU_DDR_CLK_CTRL_AHB_POST_DIV_SHIFT) &
333 		  AR934X_PLL_CPU_DDR_CLK_CTRL_AHB_POST_DIV_MASK;
334 
335 	if (clk_ctrl & AR934X_PLL_CPU_DDR_CLK_CTRL_AHB_PLL_BYPASS)
336 		ahb_rate = ref_rate;
337 	else if (clk_ctrl & AR934X_PLL_CPU_DDR_CLK_CTRL_AHBCLK_FROM_DDRPLL)
338 		ahb_rate = ddr_pll / (postdiv + 1);
339 	else
340 		ahb_rate = cpu_pll / (postdiv + 1);
341 
342 	ath79_add_sys_clkdev("ref", ref_rate);
343 	ath79_add_sys_clkdev("cpu", cpu_rate);
344 	ath79_add_sys_clkdev("ddr", ddr_rate);
345 	ath79_add_sys_clkdev("ahb", ahb_rate);
346 
347 	clk_add_alias("wdt", NULL, "ref", NULL);
348 	clk_add_alias("uart", NULL, "ref", NULL);
349 
350 	iounmap(dpll_base);
351 }
352 
353 static void __init qca955x_clocks_init(void)
354 {
355 	unsigned long ref_rate;
356 	unsigned long cpu_rate;
357 	unsigned long ddr_rate;
358 	unsigned long ahb_rate;
359 	u32 pll, out_div, ref_div, nint, frac, clk_ctrl, postdiv;
360 	u32 cpu_pll, ddr_pll;
361 	u32 bootstrap;
362 
363 	bootstrap = ath79_reset_rr(QCA955X_RESET_REG_BOOTSTRAP);
364 	if (bootstrap &	QCA955X_BOOTSTRAP_REF_CLK_40)
365 		ref_rate = 40 * 1000 * 1000;
366 	else
367 		ref_rate = 25 * 1000 * 1000;
368 
369 	pll = ath79_pll_rr(QCA955X_PLL_CPU_CONFIG_REG);
370 	out_div = (pll >> QCA955X_PLL_CPU_CONFIG_OUTDIV_SHIFT) &
371 		  QCA955X_PLL_CPU_CONFIG_OUTDIV_MASK;
372 	ref_div = (pll >> QCA955X_PLL_CPU_CONFIG_REFDIV_SHIFT) &
373 		  QCA955X_PLL_CPU_CONFIG_REFDIV_MASK;
374 	nint = (pll >> QCA955X_PLL_CPU_CONFIG_NINT_SHIFT) &
375 	       QCA955X_PLL_CPU_CONFIG_NINT_MASK;
376 	frac = (pll >> QCA955X_PLL_CPU_CONFIG_NFRAC_SHIFT) &
377 	       QCA955X_PLL_CPU_CONFIG_NFRAC_MASK;
378 
379 	cpu_pll = nint * ref_rate / ref_div;
380 	cpu_pll += frac * ref_rate / (ref_div * (1 << 6));
381 	cpu_pll /= (1 << out_div);
382 
383 	pll = ath79_pll_rr(QCA955X_PLL_DDR_CONFIG_REG);
384 	out_div = (pll >> QCA955X_PLL_DDR_CONFIG_OUTDIV_SHIFT) &
385 		  QCA955X_PLL_DDR_CONFIG_OUTDIV_MASK;
386 	ref_div = (pll >> QCA955X_PLL_DDR_CONFIG_REFDIV_SHIFT) &
387 		  QCA955X_PLL_DDR_CONFIG_REFDIV_MASK;
388 	nint = (pll >> QCA955X_PLL_DDR_CONFIG_NINT_SHIFT) &
389 	       QCA955X_PLL_DDR_CONFIG_NINT_MASK;
390 	frac = (pll >> QCA955X_PLL_DDR_CONFIG_NFRAC_SHIFT) &
391 	       QCA955X_PLL_DDR_CONFIG_NFRAC_MASK;
392 
393 	ddr_pll = nint * ref_rate / ref_div;
394 	ddr_pll += frac * ref_rate / (ref_div * (1 << 10));
395 	ddr_pll /= (1 << out_div);
396 
397 	clk_ctrl = ath79_pll_rr(QCA955X_PLL_CLK_CTRL_REG);
398 
399 	postdiv = (clk_ctrl >> QCA955X_PLL_CLK_CTRL_CPU_POST_DIV_SHIFT) &
400 		  QCA955X_PLL_CLK_CTRL_CPU_POST_DIV_MASK;
401 
402 	if (clk_ctrl & QCA955X_PLL_CLK_CTRL_CPU_PLL_BYPASS)
403 		cpu_rate = ref_rate;
404 	else if (clk_ctrl & QCA955X_PLL_CLK_CTRL_CPUCLK_FROM_CPUPLL)
405 		cpu_rate = ddr_pll / (postdiv + 1);
406 	else
407 		cpu_rate = cpu_pll / (postdiv + 1);
408 
409 	postdiv = (clk_ctrl >> QCA955X_PLL_CLK_CTRL_DDR_POST_DIV_SHIFT) &
410 		  QCA955X_PLL_CLK_CTRL_DDR_POST_DIV_MASK;
411 
412 	if (clk_ctrl & QCA955X_PLL_CLK_CTRL_DDR_PLL_BYPASS)
413 		ddr_rate = ref_rate;
414 	else if (clk_ctrl & QCA955X_PLL_CLK_CTRL_DDRCLK_FROM_DDRPLL)
415 		ddr_rate = cpu_pll / (postdiv + 1);
416 	else
417 		ddr_rate = ddr_pll / (postdiv + 1);
418 
419 	postdiv = (clk_ctrl >> QCA955X_PLL_CLK_CTRL_AHB_POST_DIV_SHIFT) &
420 		  QCA955X_PLL_CLK_CTRL_AHB_POST_DIV_MASK;
421 
422 	if (clk_ctrl & QCA955X_PLL_CLK_CTRL_AHB_PLL_BYPASS)
423 		ahb_rate = ref_rate;
424 	else if (clk_ctrl & QCA955X_PLL_CLK_CTRL_AHBCLK_FROM_DDRPLL)
425 		ahb_rate = ddr_pll / (postdiv + 1);
426 	else
427 		ahb_rate = cpu_pll / (postdiv + 1);
428 
429 	ath79_add_sys_clkdev("ref", ref_rate);
430 	ath79_add_sys_clkdev("cpu", cpu_rate);
431 	ath79_add_sys_clkdev("ddr", ddr_rate);
432 	ath79_add_sys_clkdev("ahb", ahb_rate);
433 
434 	clk_add_alias("wdt", NULL, "ref", NULL);
435 	clk_add_alias("uart", NULL, "ref", NULL);
436 }
437 
438 void __init ath79_clocks_init(void)
439 {
440 	if (soc_is_ar71xx())
441 		ar71xx_clocks_init();
442 	else if (soc_is_ar724x())
443 		ar724x_clocks_init();
444 	else if (soc_is_ar913x())
445 		ar913x_clocks_init();
446 	else if (soc_is_ar933x())
447 		ar933x_clocks_init();
448 	else if (soc_is_ar934x())
449 		ar934x_clocks_init();
450 	else if (soc_is_qca955x())
451 		qca955x_clocks_init();
452 	else
453 		BUG();
454 }
455 
456 unsigned long __init
457 ath79_get_sys_clk_rate(const char *id)
458 {
459 	struct clk *clk;
460 	unsigned long rate;
461 
462 	clk = clk_get(NULL, id);
463 	if (IS_ERR(clk))
464 		panic("unable to get %s clock, err=%d", id, (int) PTR_ERR(clk));
465 
466 	rate = clk_get_rate(clk);
467 	clk_put(clk);
468 
469 	return rate;
470 }
471 
472 /*
473  * Linux clock API
474  */
475 int clk_enable(struct clk *clk)
476 {
477 	return 0;
478 }
479 EXPORT_SYMBOL(clk_enable);
480 
481 void clk_disable(struct clk *clk)
482 {
483 }
484 EXPORT_SYMBOL(clk_disable);
485 
486 unsigned long clk_get_rate(struct clk *clk)
487 {
488 	return clk->rate;
489 }
490 EXPORT_SYMBOL(clk_get_rate);
491