1 // SPDX-License-Identifier: GPL-2.0
2 //
3 // General Purpose SPI multiplexer
4
5 #include <linux/err.h>
6 #include <linux/kernel.h>
7 #include <linux/module.h>
8 #include <linux/mux/consumer.h>
9 #include <linux/slab.h>
10 #include <linux/spi/spi.h>
11
12 #define SPI_MUX_NO_CS ((unsigned int)-1)
13
14 /**
15 * DOC: Driver description
16 *
17 * This driver supports a MUX on an SPI bus. This can be useful when you need
18 * more chip selects than the hardware peripherals support, or than are
19 * available in a particular board setup.
20 *
21 * The driver will create an additional SPI controller. Devices added under the
22 * mux will be handled as 'chip selects' on this controller.
23 */
24
25 /**
26 * struct spi_mux_priv - the basic spi_mux structure
27 * @spi: pointer to the device struct attached to the parent
28 * spi controller
29 * @current_cs: The current chip select set in the mux
30 * @child_msg_complete: The mux replaces the complete callback in the child's
31 * message to its own callback; this field is used by the
32 * driver to store the child's callback during a transfer
33 * @child_msg_context: Used to store the child's context to the callback
34 * @child_msg_dev: Used to store the spi_device pointer to the child
35 * @mux: mux_control structure used to provide chip selects for
36 * downstream spi devices
37 */
38 struct spi_mux_priv {
39 struct spi_device *spi;
40 unsigned int current_cs;
41
42 void (*child_msg_complete)(void *context);
43 void *child_msg_context;
44 struct spi_device *child_msg_dev;
45 struct mux_control *mux;
46 };
47
48 /* should not get called when the parent controller is doing a transfer */
spi_mux_select(struct spi_device * spi)49 static int spi_mux_select(struct spi_device *spi)
50 {
51 struct spi_mux_priv *priv = spi_controller_get_devdata(spi->controller);
52 int ret;
53
54 ret = mux_control_select(priv->mux, spi->chip_select);
55 if (ret)
56 return ret;
57
58 if (priv->current_cs == spi->chip_select)
59 return 0;
60
61 dev_dbg(&priv->spi->dev, "setting up the mux for cs %d\n",
62 spi->chip_select);
63
64 /* copy the child device's settings except for the cs */
65 priv->spi->max_speed_hz = spi->max_speed_hz;
66 priv->spi->mode = spi->mode;
67 priv->spi->bits_per_word = spi->bits_per_word;
68
69 priv->current_cs = spi->chip_select;
70
71 return 0;
72 }
73
spi_mux_setup(struct spi_device * spi)74 static int spi_mux_setup(struct spi_device *spi)
75 {
76 struct spi_mux_priv *priv = spi_controller_get_devdata(spi->controller);
77
78 /*
79 * can be called multiple times, won't do a valid setup now but we will
80 * change the settings when we do a transfer (necessary because we
81 * can't predict from which device it will be anyway)
82 */
83 return spi_setup(priv->spi);
84 }
85
spi_mux_complete_cb(void * context)86 static void spi_mux_complete_cb(void *context)
87 {
88 struct spi_mux_priv *priv = (struct spi_mux_priv *)context;
89 struct spi_controller *ctlr = spi_get_drvdata(priv->spi);
90 struct spi_message *m = ctlr->cur_msg;
91
92 m->complete = priv->child_msg_complete;
93 m->context = priv->child_msg_context;
94 m->spi = priv->child_msg_dev;
95 spi_finalize_current_message(ctlr);
96 mux_control_deselect(priv->mux);
97 }
98
spi_mux_transfer_one_message(struct spi_controller * ctlr,struct spi_message * m)99 static int spi_mux_transfer_one_message(struct spi_controller *ctlr,
100 struct spi_message *m)
101 {
102 struct spi_mux_priv *priv = spi_controller_get_devdata(ctlr);
103 struct spi_device *spi = m->spi;
104 int ret;
105
106 ret = spi_mux_select(spi);
107 if (ret)
108 return ret;
109
110 /*
111 * Replace the complete callback, context and spi_device with our own
112 * pointers. Save originals
113 */
114 priv->child_msg_complete = m->complete;
115 priv->child_msg_context = m->context;
116 priv->child_msg_dev = m->spi;
117
118 m->complete = spi_mux_complete_cb;
119 m->context = priv;
120 m->spi = priv->spi;
121
122 /* do the transfer */
123 return spi_async(priv->spi, m);
124 }
125
spi_mux_probe(struct spi_device * spi)126 static int spi_mux_probe(struct spi_device *spi)
127 {
128 struct spi_controller *ctlr;
129 struct spi_mux_priv *priv;
130 int ret;
131
132 ctlr = spi_alloc_master(&spi->dev, sizeof(*priv));
133 if (!ctlr)
134 return -ENOMEM;
135
136 spi_set_drvdata(spi, ctlr);
137 priv = spi_controller_get_devdata(ctlr);
138 priv->spi = spi;
139
140 /*
141 * Increase lockdep class as these lock are taken while the parent bus
142 * already holds their instance's lock.
143 */
144 lockdep_set_subclass(&ctlr->io_mutex, 1);
145 lockdep_set_subclass(&ctlr->add_lock, 1);
146
147 priv->mux = devm_mux_control_get(&spi->dev, NULL);
148 if (IS_ERR(priv->mux)) {
149 ret = dev_err_probe(&spi->dev, PTR_ERR(priv->mux),
150 "failed to get control-mux\n");
151 goto err_put_ctlr;
152 }
153
154 priv->current_cs = SPI_MUX_NO_CS;
155
156 /* supported modes are the same as our parent's */
157 ctlr->mode_bits = spi->controller->mode_bits;
158 ctlr->flags = spi->controller->flags;
159 ctlr->transfer_one_message = spi_mux_transfer_one_message;
160 ctlr->setup = spi_mux_setup;
161 ctlr->num_chipselect = mux_control_states(priv->mux);
162 ctlr->bus_num = -1;
163 ctlr->dev.of_node = spi->dev.of_node;
164 ctlr->must_async = true;
165
166 ret = devm_spi_register_controller(&spi->dev, ctlr);
167 if (ret)
168 goto err_put_ctlr;
169
170 return 0;
171
172 err_put_ctlr:
173 spi_controller_put(ctlr);
174
175 return ret;
176 }
177
178 static const struct spi_device_id spi_mux_id[] = {
179 { "spi-mux" },
180 { }
181 };
182 MODULE_DEVICE_TABLE(spi, spi_mux_id);
183
184 static const struct of_device_id spi_mux_of_match[] = {
185 { .compatible = "spi-mux" },
186 { }
187 };
188 MODULE_DEVICE_TABLE(of, spi_mux_of_match);
189
190 static struct spi_driver spi_mux_driver = {
191 .probe = spi_mux_probe,
192 .driver = {
193 .name = "spi-mux",
194 .of_match_table = spi_mux_of_match,
195 },
196 .id_table = spi_mux_id,
197 };
198
199 module_spi_driver(spi_mux_driver);
200
201 MODULE_DESCRIPTION("SPI multiplexer");
202 MODULE_LICENSE("GPL");
203
