1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * cpu-sa1100.c: clock scaling for the SA1100
4 *
5 * Copyright (C) 2000 2001, The Delft University of Technology
6 *
7 * Authors:
8 * - Johan Pouwelse (J.A.Pouwelse@its.tudelft.nl): initial version
9 * - Erik Mouw (J.A.K.Mouw@its.tudelft.nl):
10 * - major rewrite for linux-2.3.99
11 * - rewritten for the more generic power management scheme in
12 * linux-2.4.5-rmk1
13 *
14 * This software has been developed while working on the LART
15 * computing board (http://www.lartmaker.nl/), which is
16 * sponsored by the Mobile Multi-media Communications
17 * (http://www.mobimedia.org/) and Ubiquitous Communications
18 * (http://www.ubicom.tudelft.nl/) projects.
19 *
20 * The authors can be reached at:
21 *
22 * Erik Mouw
23 * Information and Communication Theory Group
24 * Faculty of Information Technology and Systems
25 * Delft University of Technology
26 * P.O. Box 5031
27 * 2600 GA Delft
28 * The Netherlands
29 *
30 * Theory of operations
31 * ====================
32 *
33 * Clock scaling can be used to lower the power consumption of the CPU
34 * core. This will give you a somewhat longer running time.
35 *
36 * The SA-1100 has a single register to change the core clock speed:
37 *
38 * PPCR 0x90020014 PLL config
39 *
40 * However, the DRAM timings are closely related to the core clock
41 * speed, so we need to change these, too. The used registers are:
42 *
43 * MDCNFG 0xA0000000 DRAM config
44 * MDCAS0 0xA0000004 Access waveform
45 * MDCAS1 0xA0000008 Access waveform
46 * MDCAS2 0xA000000C Access waveform
47 *
48 * Care must be taken to change the DRAM parameters the correct way,
49 * because otherwise the DRAM becomes unusable and the kernel will
50 * crash.
51 *
52 * The simple solution to avoid a kernel crash is to put the actual
53 * clock change in ROM and jump to that code from the kernel. The main
54 * disadvantage is that the ROM has to be modified, which is not
55 * possible on all SA-1100 platforms. Another disadvantage is that
56 * jumping to ROM makes clock switching unnecessary complicated.
57 *
58 * The idea behind this driver is that the memory configuration can be
59 * changed while running from DRAM (even with interrupts turned on!)
60 * as long as all re-configuration steps yield a valid DRAM
61 * configuration. The advantages are clear: it will run on all SA-1100
62 * platforms, and the code is very simple.
63 *
64 * If you really want to understand what is going on in
65 * sa1100_update_dram_timings(), you'll have to read sections 8.2,
66 * 9.5.7.3, and 10.2 from the "Intel StrongARM SA-1100 Microprocessor
67 * Developers Manual" (available for free from Intel).
68 */
69
70 #include <linux/kernel.h>
71 #include <linux/types.h>
72 #include <linux/init.h>
73 #include <linux/cpufreq.h>
74 #include <linux/io.h>
75
76 #include <asm/cputype.h>
77
78 #include <mach/generic.h>
79 #include <mach/hardware.h>
80
81 struct sa1100_dram_regs {
82 int speed;
83 u32 mdcnfg;
84 u32 mdcas0;
85 u32 mdcas1;
86 u32 mdcas2;
87 };
88
89
90 static struct cpufreq_driver sa1100_driver;
91
92 static struct sa1100_dram_regs sa1100_dram_settings[] = {
93 /*speed, mdcnfg, mdcas0, mdcas1, mdcas2, clock freq */
94 { 59000, 0x00dc88a3, 0xcccccccf, 0xfffffffc, 0xffffffff},/* 59.0 MHz */
95 { 73700, 0x011490a3, 0xcccccccf, 0xfffffffc, 0xffffffff},/* 73.7 MHz */
96 { 88500, 0x014e90a3, 0xcccccccf, 0xfffffffc, 0xffffffff},/* 88.5 MHz */
97 {103200, 0x01889923, 0xcccccccf, 0xfffffffc, 0xffffffff},/* 103.2 MHz */
98 {118000, 0x01c29923, 0x9999998f, 0xfffffff9, 0xffffffff},/* 118.0 MHz */
99 {132700, 0x01fb2123, 0x9999998f, 0xfffffff9, 0xffffffff},/* 132.7 MHz */
100 {147500, 0x02352123, 0x3333330f, 0xfffffff3, 0xffffffff},/* 147.5 MHz */
101 {162200, 0x026b29a3, 0x38e38e1f, 0xfff8e38e, 0xffffffff},/* 162.2 MHz */
102 {176900, 0x02a329a3, 0x71c71c1f, 0xfff1c71c, 0xffffffff},/* 176.9 MHz */
103 {191700, 0x02dd31a3, 0xe38e383f, 0xffe38e38, 0xffffffff},/* 191.7 MHz */
104 {206400, 0x03153223, 0xc71c703f, 0xffc71c71, 0xffffffff},/* 206.4 MHz */
105 {221200, 0x034fba23, 0xc71c703f, 0xffc71c71, 0xffffffff},/* 221.2 MHz */
106 {235900, 0x03853a23, 0xe1e1e07f, 0xe1e1e1e1, 0xffffffe1},/* 235.9 MHz */
107 {250700, 0x03bf3aa3, 0xc3c3c07f, 0xc3c3c3c3, 0xffffffc3},/* 250.7 MHz */
108 {265400, 0x03f7c2a3, 0xc3c3c07f, 0xc3c3c3c3, 0xffffffc3},/* 265.4 MHz */
109 {280200, 0x0431c2a3, 0x878780ff, 0x87878787, 0xffffff87},/* 280.2 MHz */
110 { 0, 0, 0, 0, 0 } /* last entry */
111 };
112
113 static void sa1100_update_dram_timings(int current_speed, int new_speed)
114 {
115 struct sa1100_dram_regs *settings = sa1100_dram_settings;
116
117 /* find speed */
118 while (settings->speed != 0) {
119 if (new_speed == settings->speed)
120 break;
121
122 settings++;
123 }
124
125 if (settings->speed == 0) {
126 panic("%s: couldn't find dram setting for speed %d\n",
127 __func__, new_speed);
128 }
129
130 /* No risk, no fun: run with interrupts on! */
131 if (new_speed > current_speed) {
132 /* We're going FASTER, so first relax the memory
133 * timings before changing the core frequency
134 */
135
136 /* Half the memory access clock */
137 MDCNFG |= MDCNFG_CDB2;
138
139 /* The order of these statements IS important, keep 8
140 * pulses!!
141 */
142 MDCAS2 = settings->mdcas2;
143 MDCAS1 = settings->mdcas1;
144 MDCAS0 = settings->mdcas0;
145 MDCNFG = settings->mdcnfg;
146 } else {
147 /* We're going SLOWER: first decrease the core
148 * frequency and then tighten the memory settings.
149 */
150
151 /* Half the memory access clock */
152 MDCNFG |= MDCNFG_CDB2;
153
154 /* The order of these statements IS important, keep 8
155 * pulses!!
156 */
157 MDCAS0 = settings->mdcas0;
158 MDCAS1 = settings->mdcas1;
159 MDCAS2 = settings->mdcas2;
160 MDCNFG = settings->mdcnfg;
161 }
162 }
163
164 static int sa1100_target(struct cpufreq_policy *policy, unsigned int ppcr)
165 {
166 unsigned int cur = sa11x0_getspeed(0);
167 unsigned int new_freq;
168
169 new_freq = sa11x0_freq_table[ppcr].frequency;
170
171 if (new_freq > cur)
172 sa1100_update_dram_timings(cur, new_freq);
173
174 PPCR = ppcr;
175
176 if (new_freq < cur)
177 sa1100_update_dram_timings(cur, new_freq);
178
179 return 0;
180 }
181
182 static int __init sa1100_cpu_init(struct cpufreq_policy *policy)
183 {
184 cpufreq_generic_init(policy, sa11x0_freq_table, 0);
185 return 0;
186 }
187
188 static struct cpufreq_driver sa1100_driver __refdata = {
189 .flags = CPUFREQ_STICKY | CPUFREQ_NEED_INITIAL_FREQ_CHECK |
190 CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING,
191 .verify = cpufreq_generic_frequency_table_verify,
192 .target_index = sa1100_target,
193 .get = sa11x0_getspeed,
194 .init = sa1100_cpu_init,
195 .name = "sa1100",
196 };
197
198 static int __init sa1100_dram_init(void)
199 {
200 if (cpu_is_sa1100())
201 return cpufreq_register_driver(&sa1100_driver);
202 else
203 return -ENODEV;
204 }
205
206 arch_initcall(sa1100_dram_init);