1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * DRM driver for Solomon SSD130X OLED displays (SPI bus)
4  *
5  * Copyright 2022 Red Hat Inc.
6  * Authors: Javier Martinez Canillas <javierm@redhat.com>
7  */
8 #include <linux/spi/spi.h>
9 #include <linux/module.h>
10 
11 #include "ssd130x.h"
12 
13 #define DRIVER_NAME	"ssd130x-spi"
14 #define DRIVER_DESC	"DRM driver for Solomon SSD130X OLED displays (SPI)"
15 
16 struct ssd130x_spi_transport {
17 	struct spi_device *spi;
18 	struct gpio_desc *dc;
19 };
20 
21 static const struct regmap_config ssd130x_spi_regmap_config = {
22 	.reg_bits = 8,
23 	.val_bits = 8,
24 };
25 
26 /*
27  * The regmap bus .write handler, it is just a wrapper around spi_write()
28  * but toggling the Data/Command control pin (D/C#). Since for 4-wire SPI
29  * a D/C# pin is used, in contrast with I2C where a control byte is sent,
30  * prior to every data byte, that contains a bit with the D/C# value.
31  *
32  * These control bytes are considered registers by the ssd130x core driver
33  * and can be used by the ssd130x SPI driver to determine if the data sent
34  * is for a command register or for the Graphic Display Data RAM (GDDRAM).
35  */
36 static int ssd130x_spi_write(void *context, const void *data, size_t count)
37 {
38 	struct ssd130x_spi_transport *t = context;
39 	struct spi_device *spi = t->spi;
40 	const u8 *reg = data;
41 
42 	if (*reg == SSD130X_COMMAND)
43 		gpiod_set_value_cansleep(t->dc, 0);
44 
45 	if (*reg == SSD130X_DATA)
46 		gpiod_set_value_cansleep(t->dc, 1);
47 
48 	/* Remove control byte since is not used in a 4-wire SPI interface */
49 	return spi_write(spi, reg + 1, count - 1);
50 }
51 
52 /* The ssd130x driver does not read registers but regmap expects a .read */
53 static int ssd130x_spi_read(void *context, const void *reg, size_t reg_size,
54 			    void *val, size_t val_size)
55 {
56 	return -EOPNOTSUPP;
57 }
58 
59 /*
60  * A custom bus is needed due the special write that toggles a D/C# pin,
61  * another option could be to just have a .reg_write() callback but that
62  * will prevent to do data writes in bulk.
63  *
64  * Once the regmap API is extended to support defining a bulk write handler
65  * in the struct regmap_config, this can be simplified and the bus dropped.
66  */
67 static struct regmap_bus regmap_ssd130x_spi_bus = {
68 	.write = ssd130x_spi_write,
69 	.read = ssd130x_spi_read,
70 };
71 
72 static int ssd130x_spi_probe(struct spi_device *spi)
73 {
74 	struct ssd130x_spi_transport *t;
75 	struct ssd130x_device *ssd130x;
76 	struct regmap *regmap;
77 	struct gpio_desc *dc;
78 	struct device *dev = &spi->dev;
79 
80 	dc = devm_gpiod_get(dev, "dc", GPIOD_OUT_LOW);
81 	if (IS_ERR(dc))
82 		return dev_err_probe(dev, PTR_ERR(dc),
83 				     "Failed to get dc gpio\n");
84 
85 	t = devm_kzalloc(dev, sizeof(*t), GFP_KERNEL);
86 	if (!t)
87 		return dev_err_probe(dev, -ENOMEM,
88 				     "Failed to allocate SPI transport data\n");
89 
90 	t->spi = spi;
91 	t->dc = dc;
92 
93 	regmap = devm_regmap_init(dev, &regmap_ssd130x_spi_bus, t,
94 				  &ssd130x_spi_regmap_config);
95 	if (IS_ERR(regmap))
96 		return PTR_ERR(regmap);
97 
98 	ssd130x = ssd130x_probe(dev, regmap);
99 	if (IS_ERR(ssd130x))
100 		return PTR_ERR(ssd130x);
101 
102 	spi_set_drvdata(spi, ssd130x);
103 
104 	return 0;
105 }
106 
107 static void ssd130x_spi_remove(struct spi_device *spi)
108 {
109 	struct ssd130x_device *ssd130x = spi_get_drvdata(spi);
110 
111 	ssd130x_remove(ssd130x);
112 }
113 
114 static void ssd130x_spi_shutdown(struct spi_device *spi)
115 {
116 	struct ssd130x_device *ssd130x = spi_get_drvdata(spi);
117 
118 	ssd130x_shutdown(ssd130x);
119 }
120 
121 static const struct of_device_id ssd130x_of_match[] = {
122 	{
123 		.compatible = "sinowealth,sh1106",
124 		.data = &ssd130x_variants[SH1106_ID],
125 	},
126 	{
127 		.compatible = "solomon,ssd1305",
128 		.data = &ssd130x_variants[SSD1305_ID],
129 	},
130 	{
131 		.compatible = "solomon,ssd1306",
132 		.data = &ssd130x_variants[SSD1306_ID],
133 	},
134 	{
135 		.compatible = "solomon,ssd1307",
136 		.data = &ssd130x_variants[SSD1307_ID],
137 	},
138 	{
139 		.compatible = "solomon,ssd1309",
140 		.data = &ssd130x_variants[SSD1309_ID],
141 	},
142 	{ /* sentinel */ }
143 };
144 MODULE_DEVICE_TABLE(of, ssd130x_of_match);
145 
146 /*
147  * The SPI core always reports a MODALIAS uevent of the form "spi:<dev>", even
148  * if the device was registered via OF. This means that the module will not be
149  * auto loaded, unless it contains an alias that matches the MODALIAS reported.
150  *
151  * To workaround this issue, add a SPI device ID table. Even when this should
152  * not be needed for this driver to match the registered SPI devices.
153  */
154 static const struct spi_device_id ssd130x_spi_table[] = {
155 	{ "sh1106",  SH1106_ID },
156 	{ "ssd1305", SSD1305_ID },
157 	{ "ssd1306", SSD1306_ID },
158 	{ "ssd1307", SSD1307_ID },
159 	{ "ssd1309", SSD1309_ID },
160 	{ /* sentinel */ }
161 };
162 MODULE_DEVICE_TABLE(spi, ssd130x_spi_table);
163 
164 static struct spi_driver ssd130x_spi_driver = {
165 	.driver = {
166 		.name = DRIVER_NAME,
167 		.of_match_table = ssd130x_of_match,
168 	},
169 	.probe = ssd130x_spi_probe,
170 	.remove = ssd130x_spi_remove,
171 	.shutdown = ssd130x_spi_shutdown,
172 };
173 module_spi_driver(ssd130x_spi_driver);
174 
175 MODULE_DESCRIPTION(DRIVER_DESC);
176 MODULE_AUTHOR("Javier Martinez Canillas <javierm@redhat.com>");
177 MODULE_LICENSE("GPL");
178 MODULE_IMPORT_NS(DRM_SSD130X);
179