1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Driver for the on-board character LCD found on some ARM reference boards
4 * This is basically an Hitachi HD44780 LCD with a custom IP block to drive it
5 * https://en.wikipedia.org/wiki/HD44780_Character_LCD
6 * Currently it will just display the text "ARM Linux" and the linux version
7 *
8 * Author: Linus Walleij <triad@df.lth.se>
9 */
10 #include <linux/completion.h>
11 #include <linux/container_of.h>
12 #include <linux/delay.h>
13 #include <linux/err.h>
14 #include <linux/init.h>
15 #include <linux/interrupt.h>
16 #include <linux/iopoll.h>
17 #include <linux/mod_devicetable.h>
18 #include <linux/platform_device.h>
19 #include <linux/string.h>
20 #include <linux/types.h>
21 #include <linux/workqueue.h>
22 #include <generated/utsrelease.h>
23
24 #define DRIVERNAME "arm-charlcd"
25 #define CHARLCD_TIMEOUT (msecs_to_jiffies(1000))
26
27 /* Offsets to registers */
28 #define CHAR_COM 0x00U
29 #define CHAR_DAT 0x04U
30 #define CHAR_RD 0x08U
31 #define CHAR_RAW 0x0CU
32 #define CHAR_MASK 0x10U
33 #define CHAR_STAT 0x14U
34
35 #define CHAR_RAW_CLEAR 0x00000000U
36 #define CHAR_RAW_VALID 0x00000100U
37
38 /* Hitachi HD44780 display commands */
39 #define HD_CLEAR 0x01U
40 #define HD_HOME 0x02U
41 #define HD_ENTRYMODE 0x04U
42 #define HD_ENTRYMODE_INCREMENT 0x02U
43 #define HD_ENTRYMODE_SHIFT 0x01U
44 #define HD_DISPCTRL 0x08U
45 #define HD_DISPCTRL_ON 0x04U
46 #define HD_DISPCTRL_CURSOR_ON 0x02U
47 #define HD_DISPCTRL_CURSOR_BLINK 0x01U
48 #define HD_CRSR_SHIFT 0x10U
49 #define HD_CRSR_SHIFT_DISPLAY 0x08U
50 #define HD_CRSR_SHIFT_DISPLAY_RIGHT 0x04U
51 #define HD_FUNCSET 0x20U
52 #define HD_FUNCSET_8BIT 0x10U
53 #define HD_FUNCSET_2_LINES 0x08U
54 #define HD_FUNCSET_FONT_5X10 0x04U
55 #define HD_SET_CGRAM 0x40U
56 #define HD_SET_DDRAM 0x80U
57 #define HD_BUSY_FLAG 0x80U
58
59 /**
60 * struct charlcd - Private data structure
61 * @dev: a pointer back to containing device
62 * @virtbase: the offset to the controller in virtual memory
63 * @irq: reserved interrupt number
64 * @complete: completion structure for the last LCD command
65 * @init_work: delayed work structure to initialize the display on boot
66 */
67 struct charlcd {
68 struct device *dev;
69 void __iomem *virtbase;
70 int irq;
71 struct completion complete;
72 struct delayed_work init_work;
73 };
74
charlcd_interrupt(int irq,void * data)75 static irqreturn_t charlcd_interrupt(int irq, void *data)
76 {
77 struct charlcd *lcd = data;
78 u8 status;
79
80 status = readl(lcd->virtbase + CHAR_STAT) & 0x01;
81 /* Clear IRQ */
82 writel(CHAR_RAW_CLEAR, lcd->virtbase + CHAR_RAW);
83 if (status)
84 complete(&lcd->complete);
85 else
86 dev_info(lcd->dev, "Spurious IRQ (%02x)\n", status);
87 return IRQ_HANDLED;
88 }
89
90
charlcd_wait_complete_irq(struct charlcd * lcd)91 static void charlcd_wait_complete_irq(struct charlcd *lcd)
92 {
93 int ret;
94
95 ret = wait_for_completion_interruptible_timeout(&lcd->complete,
96 CHARLCD_TIMEOUT);
97 /* Disable IRQ after completion */
98 writel(0x00, lcd->virtbase + CHAR_MASK);
99
100 if (ret < 0) {
101 dev_err(lcd->dev,
102 "wait_for_completion_interruptible_timeout() returned %d waiting for ready\n",
103 ret);
104 return;
105 }
106
107 if (ret == 0) {
108 dev_err(lcd->dev, "charlcd controller timed out waiting for ready\n");
109 return;
110 }
111 }
112
charlcd_4bit_read_char(struct charlcd * lcd)113 static u8 charlcd_4bit_read_char(struct charlcd *lcd)
114 {
115 u8 data;
116 u32 val;
117
118 /* If we can, use an IRQ to wait for the data, else poll */
119 if (lcd->irq >= 0)
120 charlcd_wait_complete_irq(lcd);
121 else {
122 udelay(100);
123 readl_poll_timeout_atomic(lcd->virtbase + CHAR_RAW, val,
124 val & CHAR_RAW_VALID, 100, 1000);
125 writel(CHAR_RAW_CLEAR, lcd->virtbase + CHAR_RAW);
126 }
127 msleep(1);
128
129 /* Read the 4 high bits of the data */
130 data = readl(lcd->virtbase + CHAR_RD) & 0xf0;
131
132 /*
133 * The second read for the low bits does not trigger an IRQ
134 * so in this case we have to poll for the 4 lower bits
135 */
136 udelay(100);
137 readl_poll_timeout_atomic(lcd->virtbase + CHAR_RAW, val,
138 val & CHAR_RAW_VALID, 100, 1000);
139 writel(CHAR_RAW_CLEAR, lcd->virtbase + CHAR_RAW);
140 msleep(1);
141
142 /* Read the 4 low bits of the data */
143 data |= (readl(lcd->virtbase + CHAR_RD) >> 4) & 0x0f;
144
145 return data;
146 }
147
charlcd_4bit_read_bf(struct charlcd * lcd)148 static bool charlcd_4bit_read_bf(struct charlcd *lcd)
149 {
150 if (lcd->irq >= 0) {
151 /*
152 * If we'll use IRQs to wait for the busyflag, clear any
153 * pending flag and enable IRQ
154 */
155 writel(CHAR_RAW_CLEAR, lcd->virtbase + CHAR_RAW);
156 init_completion(&lcd->complete);
157 writel(0x01, lcd->virtbase + CHAR_MASK);
158 }
159 readl(lcd->virtbase + CHAR_COM);
160
161 return charlcd_4bit_read_char(lcd) & HD_BUSY_FLAG;
162 }
163
charlcd_4bit_wait_busy(struct charlcd * lcd)164 static void charlcd_4bit_wait_busy(struct charlcd *lcd)
165 {
166 int retries = 50;
167
168 udelay(100);
169 while (charlcd_4bit_read_bf(lcd) && retries)
170 retries--;
171 if (!retries)
172 dev_err(lcd->dev, "timeout waiting for busyflag\n");
173 }
174
charlcd_4bit_command(struct charlcd * lcd,u8 cmd)175 static void charlcd_4bit_command(struct charlcd *lcd, u8 cmd)
176 {
177 u32 cmdlo = (cmd << 4) & 0xf0;
178 u32 cmdhi = (cmd & 0xf0);
179
180 writel(cmdhi, lcd->virtbase + CHAR_COM);
181 udelay(10);
182 writel(cmdlo, lcd->virtbase + CHAR_COM);
183 charlcd_4bit_wait_busy(lcd);
184 }
185
charlcd_4bit_char(struct charlcd * lcd,u8 ch)186 static void charlcd_4bit_char(struct charlcd *lcd, u8 ch)
187 {
188 u32 chlo = (ch << 4) & 0xf0;
189 u32 chhi = (ch & 0xf0);
190
191 writel(chhi, lcd->virtbase + CHAR_DAT);
192 udelay(10);
193 writel(chlo, lcd->virtbase + CHAR_DAT);
194 charlcd_4bit_wait_busy(lcd);
195 }
196
charlcd_4bit_print(struct charlcd * lcd,int line,const char * str)197 static void charlcd_4bit_print(struct charlcd *lcd, int line, const char *str)
198 {
199 u8 offset;
200 int i;
201
202 /*
203 * We support line 0, 1
204 * Line 1 runs from 0x00..0x27
205 * Line 2 runs from 0x28..0x4f
206 */
207 if (line == 0)
208 offset = 0;
209 else if (line == 1)
210 offset = 0x28;
211 else
212 return;
213
214 /* Set offset */
215 charlcd_4bit_command(lcd, HD_SET_DDRAM | offset);
216
217 /* Send string */
218 for (i = 0; i < strlen(str) && i < 0x28; i++)
219 charlcd_4bit_char(lcd, str[i]);
220 }
221
charlcd_4bit_init(struct charlcd * lcd)222 static void charlcd_4bit_init(struct charlcd *lcd)
223 {
224 /* These commands cannot be checked with the busy flag */
225 writel(HD_FUNCSET | HD_FUNCSET_8BIT, lcd->virtbase + CHAR_COM);
226 msleep(5);
227 writel(HD_FUNCSET | HD_FUNCSET_8BIT, lcd->virtbase + CHAR_COM);
228 udelay(100);
229 writel(HD_FUNCSET | HD_FUNCSET_8BIT, lcd->virtbase + CHAR_COM);
230 udelay(100);
231 /* Go to 4bit mode */
232 writel(HD_FUNCSET, lcd->virtbase + CHAR_COM);
233 udelay(100);
234 /*
235 * 4bit mode, 2 lines, 5x8 font, after this the number of lines
236 * and the font cannot be changed until the next initialization sequence
237 */
238 charlcd_4bit_command(lcd, HD_FUNCSET | HD_FUNCSET_2_LINES);
239 charlcd_4bit_command(lcd, HD_DISPCTRL | HD_DISPCTRL_ON);
240 charlcd_4bit_command(lcd, HD_ENTRYMODE | HD_ENTRYMODE_INCREMENT);
241 charlcd_4bit_command(lcd, HD_CLEAR);
242 charlcd_4bit_command(lcd, HD_HOME);
243 /* Put something useful in the display */
244 charlcd_4bit_print(lcd, 0, "ARM Linux");
245 charlcd_4bit_print(lcd, 1, UTS_RELEASE);
246 }
247
charlcd_init_work(struct work_struct * work)248 static void charlcd_init_work(struct work_struct *work)
249 {
250 struct charlcd *lcd =
251 container_of(work, struct charlcd, init_work.work);
252
253 charlcd_4bit_init(lcd);
254 }
255
charlcd_probe(struct platform_device * pdev)256 static int __init charlcd_probe(struct platform_device *pdev)
257 {
258 struct device *dev = &pdev->dev;
259 int ret;
260 struct charlcd *lcd;
261
262 lcd = devm_kzalloc(dev, sizeof(*lcd), GFP_KERNEL);
263 if (!lcd)
264 return -ENOMEM;
265
266 lcd->dev = &pdev->dev;
267
268 lcd->virtbase = devm_platform_ioremap_resource(pdev, 0);
269 if (IS_ERR(lcd->virtbase))
270 return PTR_ERR(lcd->virtbase);
271
272 lcd->irq = platform_get_irq(pdev, 0);
273 /* If no IRQ is supplied, we'll survive without it */
274 if (lcd->irq >= 0) {
275 ret = devm_request_irq(dev, lcd->irq, charlcd_interrupt, 0, DRIVERNAME, lcd);
276 if (ret)
277 return ret;
278 }
279
280 platform_set_drvdata(pdev, lcd);
281
282 /*
283 * Initialize the display in a delayed work, because
284 * it is VERY slow and would slow down the boot of the system.
285 */
286 INIT_DELAYED_WORK(&lcd->init_work, charlcd_init_work);
287 schedule_delayed_work(&lcd->init_work, 0);
288
289 return 0;
290 }
291
charlcd_suspend(struct device * dev)292 static int charlcd_suspend(struct device *dev)
293 {
294 struct charlcd *lcd = dev_get_drvdata(dev);
295
296 /* Power the display off */
297 charlcd_4bit_command(lcd, HD_DISPCTRL);
298 return 0;
299 }
300
charlcd_resume(struct device * dev)301 static int charlcd_resume(struct device *dev)
302 {
303 struct charlcd *lcd = dev_get_drvdata(dev);
304
305 /* Turn the display back on */
306 charlcd_4bit_command(lcd, HD_DISPCTRL | HD_DISPCTRL_ON);
307 return 0;
308 }
309
310 static const struct dev_pm_ops charlcd_pm_ops = {
311 .suspend = charlcd_suspend,
312 .resume = charlcd_resume,
313 };
314
315 static const struct of_device_id charlcd_match[] = {
316 { .compatible = "arm,versatile-lcd", },
317 {}
318 };
319
320 static struct platform_driver charlcd_driver = {
321 .driver = {
322 .name = DRIVERNAME,
323 .pm = &charlcd_pm_ops,
324 .suppress_bind_attrs = true,
325 .of_match_table = charlcd_match,
326 },
327 };
328 builtin_platform_driver_probe(charlcd_driver, charlcd_probe);
329