1 /*
2  *  Copyright (C) 2013 Google, Inc
3  *
4  *  This program is free software; you can redistribute it and/or modify
5  *  it under the terms of the GNU General Public License as published by
6  *  the Free Software Foundation; either version 2 of the License, or
7  *  (at your option) any later version.
8  *
9  * Expose an I2C passthrough to the ChromeOS EC.
10  */
11 
12 #include <linux/module.h>
13 #include <linux/i2c.h>
14 #include <linux/mfd/cros_ec.h>
15 #include <linux/mfd/cros_ec_commands.h>
16 #include <linux/platform_device.h>
17 #include <linux/slab.h>
18 
19 #define I2C_MAX_RETRIES 3
20 
21 /**
22  * struct ec_i2c_device - Driver data for I2C tunnel
23  *
24  * @dev: Device node
25  * @adap: I2C adapter
26  * @ec: Pointer to EC device
27  * @remote_bus: The EC bus number we tunnel to on the other side.
28  * @request_buf: Buffer for transmitting data; we expect most transfers to fit.
29  * @response_buf: Buffer for receiving data; we expect most transfers to fit.
30  */
31 
32 struct ec_i2c_device {
33 	struct device *dev;
34 	struct i2c_adapter adap;
35 	struct cros_ec_device *ec;
36 
37 	u16 remote_bus;
38 
39 	u8 request_buf[256];
40 	u8 response_buf[256];
41 };
42 
43 /**
44  * ec_i2c_count_message - Count bytes needed for ec_i2c_construct_message
45  *
46  * @i2c_msgs: The i2c messages to read
47  * @num: The number of i2c messages.
48  *
49  * Returns the number of bytes the messages will take up.
50  */
51 static int ec_i2c_count_message(const struct i2c_msg i2c_msgs[], int num)
52 {
53 	int i;
54 	int size;
55 
56 	size = sizeof(struct ec_params_i2c_passthru);
57 	size += num * sizeof(struct ec_params_i2c_passthru_msg);
58 	for (i = 0; i < num; i++)
59 		if (!(i2c_msgs[i].flags & I2C_M_RD))
60 			size += i2c_msgs[i].len;
61 
62 	return size;
63 }
64 
65 /**
66  * ec_i2c_construct_message - construct a message to go to the EC
67  *
68  * This function effectively stuffs the standard i2c_msg format of Linux into
69  * a format that the EC understands.
70  *
71  * @buf: The buffer to fill.  We assume that the buffer is big enough.
72  * @i2c_msgs: The i2c messages to read.
73  * @num: The number of i2c messages.
74  * @bus_num: The remote bus number we want to talk to.
75  *
76  * Returns 0 or a negative error number.
77  */
78 static int ec_i2c_construct_message(u8 *buf, const struct i2c_msg i2c_msgs[],
79 				    int num, u16 bus_num)
80 {
81 	struct ec_params_i2c_passthru *params;
82 	u8 *out_data;
83 	int i;
84 
85 	out_data = buf + sizeof(struct ec_params_i2c_passthru) +
86 		   num * sizeof(struct ec_params_i2c_passthru_msg);
87 
88 	params = (struct ec_params_i2c_passthru *)buf;
89 	params->port = bus_num;
90 	params->num_msgs = num;
91 	for (i = 0; i < num; i++) {
92 		const struct i2c_msg *i2c_msg = &i2c_msgs[i];
93 		struct ec_params_i2c_passthru_msg *msg = &params->msg[i];
94 
95 		msg->len = i2c_msg->len;
96 		msg->addr_flags = i2c_msg->addr;
97 
98 		if (i2c_msg->flags & I2C_M_TEN)
99 			return -EINVAL;
100 
101 		if (i2c_msg->flags & I2C_M_RD) {
102 			msg->addr_flags |= EC_I2C_FLAG_READ;
103 		} else {
104 			memcpy(out_data, i2c_msg->buf, msg->len);
105 			out_data += msg->len;
106 		}
107 	}
108 
109 	return 0;
110 }
111 
112 /**
113  * ec_i2c_count_response - Count bytes needed for ec_i2c_parse_response
114  *
115  * @i2c_msgs: The i2c messages to to fill up.
116  * @num: The number of i2c messages expected.
117  *
118  * Returns the number of response bytes expeced.
119  */
120 static int ec_i2c_count_response(struct i2c_msg i2c_msgs[], int num)
121 {
122 	int size;
123 	int i;
124 
125 	size = sizeof(struct ec_response_i2c_passthru);
126 	for (i = 0; i < num; i++)
127 		if (i2c_msgs[i].flags & I2C_M_RD)
128 			size += i2c_msgs[i].len;
129 
130 	return size;
131 }
132 
133 /**
134  * ec_i2c_parse_response - Parse a response from the EC
135  *
136  * We'll take the EC's response and copy it back into msgs.
137  *
138  * @buf: The buffer to parse.
139  * @i2c_msgs: The i2c messages to to fill up.
140  * @num: The number of i2c messages; will be modified to include the actual
141  *	 number received.
142  *
143  * Returns 0 or a negative error number.
144  */
145 static int ec_i2c_parse_response(const u8 *buf, struct i2c_msg i2c_msgs[],
146 				 int *num)
147 {
148 	const struct ec_response_i2c_passthru *resp;
149 	const u8 *in_data;
150 	int i;
151 
152 	in_data = buf + sizeof(struct ec_response_i2c_passthru);
153 
154 	resp = (const struct ec_response_i2c_passthru *)buf;
155 	if (resp->i2c_status & EC_I2C_STATUS_TIMEOUT)
156 		return -ETIMEDOUT;
157 	else if (resp->i2c_status & EC_I2C_STATUS_ERROR)
158 		return -EREMOTEIO;
159 
160 	/* Other side could send us back fewer messages, but not more */
161 	if (resp->num_msgs > *num)
162 		return -EPROTO;
163 	*num = resp->num_msgs;
164 
165 	for (i = 0; i < *num; i++) {
166 		struct i2c_msg *i2c_msg = &i2c_msgs[i];
167 
168 		if (i2c_msgs[i].flags & I2C_M_RD) {
169 			memcpy(i2c_msg->buf, in_data, i2c_msg->len);
170 			in_data += i2c_msg->len;
171 		}
172 	}
173 
174 	return 0;
175 }
176 
177 static int ec_i2c_xfer(struct i2c_adapter *adap, struct i2c_msg i2c_msgs[],
178 		       int num)
179 {
180 	struct ec_i2c_device *bus = adap->algo_data;
181 	struct device *dev = bus->dev;
182 	const u16 bus_num = bus->remote_bus;
183 	int request_len;
184 	int response_len;
185 	int alloc_size;
186 	int result;
187 	struct cros_ec_command *msg;
188 
189 	request_len = ec_i2c_count_message(i2c_msgs, num);
190 	if (request_len < 0) {
191 		dev_warn(dev, "Error constructing message %d\n", request_len);
192 		return request_len;
193 	}
194 
195 	response_len = ec_i2c_count_response(i2c_msgs, num);
196 	if (response_len < 0) {
197 		/* Unexpected; no errors should come when NULL response */
198 		dev_warn(dev, "Error preparing response %d\n", response_len);
199 		return response_len;
200 	}
201 
202 	alloc_size = max(request_len, response_len);
203 	msg = kmalloc(sizeof(*msg) + alloc_size, GFP_KERNEL);
204 	if (!msg)
205 		return -ENOMEM;
206 
207 	result = ec_i2c_construct_message(msg->data, i2c_msgs, num, bus_num);
208 	if (result) {
209 		dev_err(dev, "Error constructing EC i2c message %d\n", result);
210 		goto exit;
211 	}
212 
213 	msg->version = 0;
214 	msg->command = EC_CMD_I2C_PASSTHRU;
215 	msg->outsize = request_len;
216 	msg->insize = response_len;
217 
218 	result = cros_ec_cmd_xfer(bus->ec, msg);
219 	if (result < 0) {
220 		dev_err(dev, "Error transferring EC i2c message %d\n", result);
221 		goto exit;
222 	}
223 
224 	result = ec_i2c_parse_response(msg->data, i2c_msgs, &num);
225 	if (result < 0) {
226 		dev_err(dev, "Error parsing EC i2c message %d\n", result);
227 		goto exit;
228 	}
229 
230 	/* Indicate success by saying how many messages were sent */
231 	result = num;
232 exit:
233 	kfree(msg);
234 	return result;
235 }
236 
237 static u32 ec_i2c_functionality(struct i2c_adapter *adap)
238 {
239 	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
240 }
241 
242 static const struct i2c_algorithm ec_i2c_algorithm = {
243 	.master_xfer	= ec_i2c_xfer,
244 	.functionality	= ec_i2c_functionality,
245 };
246 
247 static int ec_i2c_probe(struct platform_device *pdev)
248 {
249 	struct device_node *np = pdev->dev.of_node;
250 	struct cros_ec_device *ec = dev_get_drvdata(pdev->dev.parent);
251 	struct device *dev = &pdev->dev;
252 	struct ec_i2c_device *bus = NULL;
253 	u32 remote_bus;
254 	int err;
255 
256 	if (!ec->cmd_xfer) {
257 		dev_err(dev, "Missing sendrecv\n");
258 		return -EINVAL;
259 	}
260 
261 	bus = devm_kzalloc(dev, sizeof(*bus), GFP_KERNEL);
262 	if (bus == NULL)
263 		return -ENOMEM;
264 
265 	err = of_property_read_u32(np, "google,remote-bus", &remote_bus);
266 	if (err) {
267 		dev_err(dev, "Couldn't read remote-bus property\n");
268 		return err;
269 	}
270 	bus->remote_bus = remote_bus;
271 
272 	bus->ec = ec;
273 	bus->dev = dev;
274 
275 	bus->adap.owner = THIS_MODULE;
276 	strlcpy(bus->adap.name, "cros-ec-i2c-tunnel", sizeof(bus->adap.name));
277 	bus->adap.algo = &ec_i2c_algorithm;
278 	bus->adap.algo_data = bus;
279 	bus->adap.dev.parent = &pdev->dev;
280 	bus->adap.dev.of_node = np;
281 	bus->adap.retries = I2C_MAX_RETRIES;
282 
283 	err = i2c_add_adapter(&bus->adap);
284 	if (err) {
285 		dev_err(dev, "cannot register i2c adapter\n");
286 		return err;
287 	}
288 	platform_set_drvdata(pdev, bus);
289 
290 	return err;
291 }
292 
293 static int ec_i2c_remove(struct platform_device *dev)
294 {
295 	struct ec_i2c_device *bus = platform_get_drvdata(dev);
296 
297 	i2c_del_adapter(&bus->adap);
298 
299 	return 0;
300 }
301 
302 #ifdef CONFIG_OF
303 static const struct of_device_id cros_ec_i2c_of_match[] = {
304 	{ .compatible = "google,cros-ec-i2c-tunnel" },
305 	{},
306 };
307 MODULE_DEVICE_TABLE(of, cros_ec_i2c_of_match);
308 #endif
309 
310 static struct platform_driver ec_i2c_tunnel_driver = {
311 	.probe = ec_i2c_probe,
312 	.remove = ec_i2c_remove,
313 	.driver = {
314 		.name = "cros-ec-i2c-tunnel",
315 		.of_match_table = of_match_ptr(cros_ec_i2c_of_match),
316 	},
317 };
318 
319 module_platform_driver(ec_i2c_tunnel_driver);
320 
321 MODULE_LICENSE("GPL");
322 MODULE_DESCRIPTION("EC I2C tunnel driver");
323 MODULE_ALIAS("platform:cros-ec-i2c-tunnel");
324