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/init.h>
11#include <linux/interrupt.h>
12#include <linux/platform_device.h>
13#include <linux/of.h>
14#include <linux/completion.h>
15#include <linux/delay.h>
16#include <linux/io.h>
17#include <linux/slab.h>
18#include <linux/workqueue.h>
19#include <generated/utsrelease.h>
20
21#define DRIVERNAME "arm-charlcd"
22#define CHARLCD_TIMEOUT (msecs_to_jiffies(1000))
23
24/* Offsets to registers */
25#define CHAR_COM	0x00U
26#define CHAR_DAT	0x04U
27#define CHAR_RD		0x08U
28#define CHAR_RAW	0x0CU
29#define CHAR_MASK	0x10U
30#define CHAR_STAT	0x14U
31
32#define CHAR_RAW_CLEAR	0x00000000U
33#define CHAR_RAW_VALID	0x00000100U
34
35/* Hitachi HD44780 display commands */
36#define HD_CLEAR			0x01U
37#define HD_HOME				0x02U
38#define HD_ENTRYMODE			0x04U
39#define HD_ENTRYMODE_INCREMENT		0x02U
40#define HD_ENTRYMODE_SHIFT		0x01U
41#define HD_DISPCTRL			0x08U
42#define HD_DISPCTRL_ON			0x04U
43#define HD_DISPCTRL_CURSOR_ON		0x02U
44#define HD_DISPCTRL_CURSOR_BLINK	0x01U
45#define HD_CRSR_SHIFT			0x10U
46#define HD_CRSR_SHIFT_DISPLAY		0x08U
47#define HD_CRSR_SHIFT_DISPLAY_RIGHT	0x04U
48#define HD_FUNCSET			0x20U
49#define HD_FUNCSET_8BIT			0x10U
50#define HD_FUNCSET_2_LINES		0x08U
51#define HD_FUNCSET_FONT_5X10		0x04U
52#define HD_SET_CGRAM			0x40U
53#define HD_SET_DDRAM			0x80U
54#define HD_BUSY_FLAG			0x80U
55
56/**
57 * struct charlcd - Private data structure
58 * @dev: a pointer back to containing device
59 * @phybase: the offset to the controller in physical memory
60 * @physize: the size of the physical page
61 * @virtbase: the offset to the controller in virtual memory
62 * @irq: reserved interrupt number
63 * @complete: completion structure for the last LCD command
64 * @init_work: delayed work structure to initialize the display on boot
65 */
66struct charlcd {
67	struct device *dev;
68	u32 phybase;
69	u32 physize;
70	void __iomem *virtbase;
71	int irq;
72	struct completion complete;
73	struct delayed_work init_work;
74};
75
76static irqreturn_t charlcd_interrupt(int irq, void *data)
77{
78	struct charlcd *lcd = data;
79	u8 status;
80
81	status = readl(lcd->virtbase + CHAR_STAT) & 0x01;
82	/* Clear IRQ */
83	writel(CHAR_RAW_CLEAR, lcd->virtbase + CHAR_RAW);
84	if (status)
85		complete(&lcd->complete);
86	else
87		dev_info(lcd->dev, "Spurious IRQ (%02x)\n", status);
88	return IRQ_HANDLED;
89}
90
91
92static void charlcd_wait_complete_irq(struct charlcd *lcd)
93{
94	int ret;
95
96	ret = wait_for_completion_interruptible_timeout(&lcd->complete,
97							CHARLCD_TIMEOUT);
98	/* Disable IRQ after completion */
99	writel(0x00, lcd->virtbase + CHAR_MASK);
100
101	if (ret < 0) {
102		dev_err(lcd->dev,
103			"wait_for_completion_interruptible_timeout() "
104			"returned %d waiting for ready\n", ret);
105		return;
106	}
107
108	if (ret == 0) {
109		dev_err(lcd->dev, "charlcd controller timed out "
110			"waiting for ready\n");
111		return;
112	}
113}
114
115static u8 charlcd_4bit_read_char(struct charlcd *lcd)
116{
117	u8 data;
118	u32 val;
119	int i;
120
121	/* If we can, use an IRQ to wait for the data, else poll */
122	if (lcd->irq >= 0)
123		charlcd_wait_complete_irq(lcd);
124	else {
125		i = 0;
126		val = 0;
127		while (!(val & CHAR_RAW_VALID) && i < 10) {
128			udelay(100);
129			val = readl(lcd->virtbase + CHAR_RAW);
130			i++;
131		}
132
133		writel(CHAR_RAW_CLEAR, lcd->virtbase + CHAR_RAW);
134	}
135	msleep(1);
136
137	/* Read the 4 high bits of the data */
138	data = readl(lcd->virtbase + CHAR_RD) & 0xf0;
139
140	/*
141	 * The second read for the low bits does not trigger an IRQ
142	 * so in this case we have to poll for the 4 lower bits
143	 */
144	i = 0;
145	val = 0;
146	while (!(val & CHAR_RAW_VALID) && i < 10) {
147		udelay(100);
148		val = readl(lcd->virtbase + CHAR_RAW);
149		i++;
150	}
151	writel(CHAR_RAW_CLEAR, lcd->virtbase + CHAR_RAW);
152	msleep(1);
153
154	/* Read the 4 low bits of the data */
155	data |= (readl(lcd->virtbase + CHAR_RD) >> 4) & 0x0f;
156
157	return data;
158}
159
160static bool charlcd_4bit_read_bf(struct charlcd *lcd)
161{
162	if (lcd->irq >= 0) {
163		/*
164		 * If we'll use IRQs to wait for the busyflag, clear any
165		 * pending flag and enable IRQ
166		 */
167		writel(CHAR_RAW_CLEAR, lcd->virtbase + CHAR_RAW);
168		init_completion(&lcd->complete);
169		writel(0x01, lcd->virtbase + CHAR_MASK);
170	}
171	readl(lcd->virtbase + CHAR_COM);
172	return charlcd_4bit_read_char(lcd) & HD_BUSY_FLAG ? true : false;
173}
174
175static void charlcd_4bit_wait_busy(struct charlcd *lcd)
176{
177	int retries = 50;
178
179	udelay(100);
180	while (charlcd_4bit_read_bf(lcd) && retries)
181		retries--;
182	if (!retries)
183		dev_err(lcd->dev, "timeout waiting for busyflag\n");
184}
185
186static void charlcd_4bit_command(struct charlcd *lcd, u8 cmd)
187{
188	u32 cmdlo = (cmd << 4) & 0xf0;
189	u32 cmdhi = (cmd & 0xf0);
190
191	writel(cmdhi, lcd->virtbase + CHAR_COM);
192	udelay(10);
193	writel(cmdlo, lcd->virtbase + CHAR_COM);
194	charlcd_4bit_wait_busy(lcd);
195}
196
197static void charlcd_4bit_char(struct charlcd *lcd, u8 ch)
198{
199	u32 chlo = (ch << 4) & 0xf0;
200	u32 chhi = (ch & 0xf0);
201
202	writel(chhi, lcd->virtbase + CHAR_DAT);
203	udelay(10);
204	writel(chlo, lcd->virtbase + CHAR_DAT);
205	charlcd_4bit_wait_busy(lcd);
206}
207
208static void charlcd_4bit_print(struct charlcd *lcd, int line, const char *str)
209{
210	u8 offset;
211	int i;
212
213	/*
214	 * We support line 0, 1
215	 * Line 1 runs from 0x00..0x27
216	 * Line 2 runs from 0x28..0x4f
217	 */
218	if (line == 0)
219		offset = 0;
220	else if (line == 1)
221		offset = 0x28;
222	else
223		return;
224
225	/* Set offset */
226	charlcd_4bit_command(lcd, HD_SET_DDRAM | offset);
227
228	/* Send string */
229	for (i = 0; i < strlen(str) && i < 0x28; i++)
230		charlcd_4bit_char(lcd, str[i]);
231}
232
233static void charlcd_4bit_init(struct charlcd *lcd)
234{
235	/* These commands cannot be checked with the busy flag */
236	writel(HD_FUNCSET | HD_FUNCSET_8BIT, lcd->virtbase + CHAR_COM);
237	msleep(5);
238	writel(HD_FUNCSET | HD_FUNCSET_8BIT, lcd->virtbase + CHAR_COM);
239	udelay(100);
240	writel(HD_FUNCSET | HD_FUNCSET_8BIT, lcd->virtbase + CHAR_COM);
241	udelay(100);
242	/* Go to 4bit mode */
243	writel(HD_FUNCSET, lcd->virtbase + CHAR_COM);
244	udelay(100);
245	/*
246	 * 4bit mode, 2 lines, 5x8 font, after this the number of lines
247	 * and the font cannot be changed until the next initialization sequence
248	 */
249	charlcd_4bit_command(lcd, HD_FUNCSET | HD_FUNCSET_2_LINES);
250	charlcd_4bit_command(lcd, HD_DISPCTRL | HD_DISPCTRL_ON);
251	charlcd_4bit_command(lcd, HD_ENTRYMODE | HD_ENTRYMODE_INCREMENT);
252	charlcd_4bit_command(lcd, HD_CLEAR);
253	charlcd_4bit_command(lcd, HD_HOME);
254	/* Put something useful in the display */
255	charlcd_4bit_print(lcd, 0, "ARM Linux");
256	charlcd_4bit_print(lcd, 1, UTS_RELEASE);
257}
258
259static void charlcd_init_work(struct work_struct *work)
260{
261	struct charlcd *lcd =
262		container_of(work, struct charlcd, init_work.work);
263
264	charlcd_4bit_init(lcd);
265}
266
267static int __init charlcd_probe(struct platform_device *pdev)
268{
269	int ret;
270	struct charlcd *lcd;
271	struct resource *res;
272
273	lcd = kzalloc(sizeof(struct charlcd), GFP_KERNEL);
274	if (!lcd)
275		return -ENOMEM;
276
277	lcd->dev = &pdev->dev;
278
279	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
280	if (!res) {
281		ret = -ENOENT;
282		goto out_no_resource;
283	}
284	lcd->phybase = res->start;
285	lcd->physize = resource_size(res);
286
287	if (request_mem_region(lcd->phybase, lcd->physize,
288			       DRIVERNAME) == NULL) {
289		ret = -EBUSY;
290		goto out_no_memregion;
291	}
292
293	lcd->virtbase = ioremap(lcd->phybase, lcd->physize);
294	if (!lcd->virtbase) {
295		ret = -ENOMEM;
296		goto out_no_memregion;
297	}
298
299	lcd->irq = platform_get_irq(pdev, 0);
300	/* If no IRQ is supplied, we'll survive without it */
301	if (lcd->irq >= 0) {
302		if (request_irq(lcd->irq, charlcd_interrupt, 0,
303				DRIVERNAME, lcd)) {
304			ret = -EIO;
305			goto out_no_irq;
306		}
307	}
308
309	platform_set_drvdata(pdev, lcd);
310
311	/*
312	 * Initialize the display in a delayed work, because
313	 * it is VERY slow and would slow down the boot of the system.
314	 */
315	INIT_DELAYED_WORK(&lcd->init_work, charlcd_init_work);
316	schedule_delayed_work(&lcd->init_work, 0);
317
318	dev_info(&pdev->dev, "initialized ARM character LCD at %08x\n",
319		lcd->phybase);
320
321	return 0;
322
323out_no_irq:
324	iounmap(lcd->virtbase);
325out_no_memregion:
326	release_mem_region(lcd->phybase, SZ_4K);
327out_no_resource:
328	kfree(lcd);
329	return ret;
330}
331
332static int charlcd_suspend(struct device *dev)
333{
334	struct charlcd *lcd = dev_get_drvdata(dev);
335
336	/* Power the display off */
337	charlcd_4bit_command(lcd, HD_DISPCTRL);
338	return 0;
339}
340
341static int charlcd_resume(struct device *dev)
342{
343	struct charlcd *lcd = dev_get_drvdata(dev);
344
345	/* Turn the display back on */
346	charlcd_4bit_command(lcd, HD_DISPCTRL | HD_DISPCTRL_ON);
347	return 0;
348}
349
350static const struct dev_pm_ops charlcd_pm_ops = {
351	.suspend = charlcd_suspend,
352	.resume = charlcd_resume,
353};
354
355static const struct of_device_id charlcd_match[] = {
356	{ .compatible = "arm,versatile-lcd", },
357	{}
358};
359
360static struct platform_driver charlcd_driver = {
361	.driver = {
362		.name = DRIVERNAME,
363		.pm = &charlcd_pm_ops,
364		.suppress_bind_attrs = true,
365		.of_match_table = of_match_ptr(charlcd_match),
366	},
367};
368builtin_platform_driver_probe(charlcd_driver, charlcd_probe);
369