1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Mailbox interface for Wilco Embedded Controller
4 *
5 * Copyright 2018 Google LLC
6 *
7 * The Wilco EC is similar to a typical ChromeOS embedded controller.
8 * It uses the same MEC based low-level communication and a similar
9 * protocol, but with some important differences. The EC firmware does
10 * not support the same mailbox commands so it is not registered as a
11 * cros_ec device type.
12 *
13 * Most messages follow a standard format, but there are some exceptions
14 * and an interface is provided to do direct/raw transactions that do not
15 * make assumptions about byte placement.
16 */
17
18 #include <linux/delay.h>
19 #include <linux/device.h>
20 #include <linux/io.h>
21 #include <linux/platform_data/wilco-ec.h>
22 #include <linux/platform_device.h>
23
24 #include "../cros_ec_lpc_mec.h"
25
26 /* Version of mailbox interface */
27 #define EC_MAILBOX_VERSION 0
28
29 /* Command to start mailbox transaction */
30 #define EC_MAILBOX_START_COMMAND 0xda
31
32 /* Version of EC protocol */
33 #define EC_MAILBOX_PROTO_VERSION 3
34
35 /* Number of header bytes to be counted as data bytes */
36 #define EC_MAILBOX_DATA_EXTRA 2
37
38 /* Maximum timeout */
39 #define EC_MAILBOX_TIMEOUT HZ
40
41 /* EC response flags */
42 #define EC_CMDR_DATA BIT(0) /* Data ready for host to read */
43 #define EC_CMDR_PENDING BIT(1) /* Write pending to EC */
44 #define EC_CMDR_BUSY BIT(2) /* EC is busy processing a command */
45 #define EC_CMDR_CMD BIT(3) /* Last host write was a command */
46
47 /**
48 * wilco_ec_response_timed_out() - Wait for EC response.
49 * @ec: EC device.
50 *
51 * Return: true if EC timed out, false if EC did not time out.
52 */
wilco_ec_response_timed_out(struct wilco_ec_device * ec)53 static bool wilco_ec_response_timed_out(struct wilco_ec_device *ec)
54 {
55 unsigned long timeout = jiffies + EC_MAILBOX_TIMEOUT;
56
57 do {
58 if (!(inb(ec->io_command->start) &
59 (EC_CMDR_PENDING | EC_CMDR_BUSY)))
60 return false;
61 usleep_range(100, 200);
62 } while (time_before(jiffies, timeout));
63
64 return true;
65 }
66
67 /**
68 * wilco_ec_checksum() - Compute 8-bit checksum over data range.
69 * @data: Data to checksum.
70 * @size: Number of bytes to checksum.
71 *
72 * Return: 8-bit checksum of provided data.
73 */
wilco_ec_checksum(const void * data,size_t size)74 static u8 wilco_ec_checksum(const void *data, size_t size)
75 {
76 u8 *data_bytes = (u8 *)data;
77 u8 checksum = 0;
78 size_t i;
79
80 for (i = 0; i < size; i++)
81 checksum += data_bytes[i];
82
83 return checksum;
84 }
85
86 /**
87 * wilco_ec_prepare() - Prepare the request structure for the EC.
88 * @msg: EC message with request information.
89 * @rq: EC request structure to fill.
90 */
wilco_ec_prepare(struct wilco_ec_message * msg,struct wilco_ec_request * rq)91 static void wilco_ec_prepare(struct wilco_ec_message *msg,
92 struct wilco_ec_request *rq)
93 {
94 memset(rq, 0, sizeof(*rq));
95 rq->struct_version = EC_MAILBOX_PROTO_VERSION;
96 rq->mailbox_id = msg->type;
97 rq->mailbox_version = EC_MAILBOX_VERSION;
98 rq->data_size = msg->request_size;
99
100 /* Checksum header and data */
101 rq->checksum = wilco_ec_checksum(rq, sizeof(*rq));
102 rq->checksum += wilco_ec_checksum(msg->request_data, msg->request_size);
103 rq->checksum = -rq->checksum;
104 }
105
106 /**
107 * wilco_ec_transfer() - Perform actual data transfer.
108 * @ec: EC device.
109 * @msg: EC message data for request and response.
110 * @rq: Filled in request structure
111 *
112 * Context: ec->mailbox_lock should be held while using this function.
113 * Return: number of bytes received or negative error code on failure.
114 */
wilco_ec_transfer(struct wilco_ec_device * ec,struct wilco_ec_message * msg,struct wilco_ec_request * rq)115 static int wilco_ec_transfer(struct wilco_ec_device *ec,
116 struct wilco_ec_message *msg,
117 struct wilco_ec_request *rq)
118 {
119 struct wilco_ec_response *rs;
120 u8 checksum;
121 u8 flag;
122
123 /* Write request header, then data */
124 cros_ec_lpc_io_bytes_mec(MEC_IO_WRITE, 0, sizeof(*rq), (u8 *)rq);
125 cros_ec_lpc_io_bytes_mec(MEC_IO_WRITE, sizeof(*rq), msg->request_size,
126 msg->request_data);
127
128 /* Start the command */
129 outb(EC_MAILBOX_START_COMMAND, ec->io_command->start);
130
131 /* For some commands (eg shutdown) the EC will not respond, that's OK */
132 if (msg->flags & WILCO_EC_FLAG_NO_RESPONSE) {
133 dev_dbg(ec->dev, "EC does not respond to this command\n");
134 return 0;
135 }
136
137 /* Wait for it to complete */
138 if (wilco_ec_response_timed_out(ec)) {
139 dev_dbg(ec->dev, "response timed out\n");
140 return -ETIMEDOUT;
141 }
142
143 /* Check result */
144 flag = inb(ec->io_data->start);
145 if (flag) {
146 dev_dbg(ec->dev, "bad response: 0x%02x\n", flag);
147 return -EIO;
148 }
149
150 /* Read back response */
151 rs = ec->data_buffer;
152 checksum = cros_ec_lpc_io_bytes_mec(MEC_IO_READ, 0,
153 sizeof(*rs) + EC_MAILBOX_DATA_SIZE,
154 (u8 *)rs);
155 if (checksum) {
156 dev_dbg(ec->dev, "bad packet checksum 0x%02x\n", rs->checksum);
157 return -EBADMSG;
158 }
159
160 if (rs->result) {
161 dev_dbg(ec->dev, "EC reported failure: 0x%02x\n", rs->result);
162 return -EBADMSG;
163 }
164
165 if (rs->data_size != EC_MAILBOX_DATA_SIZE) {
166 dev_dbg(ec->dev, "unexpected packet size (%u != %u)\n",
167 rs->data_size, EC_MAILBOX_DATA_SIZE);
168 return -EMSGSIZE;
169 }
170
171 if (rs->data_size < msg->response_size) {
172 dev_dbg(ec->dev, "EC didn't return enough data (%u < %zu)\n",
173 rs->data_size, msg->response_size);
174 return -EMSGSIZE;
175 }
176
177 memcpy(msg->response_data, rs->data, msg->response_size);
178
179 return rs->data_size;
180 }
181
182 /**
183 * wilco_ec_mailbox() - Send EC request and receive EC response.
184 * @ec: EC device.
185 * @msg: EC message data for request and response.
186 *
187 * On entry msg->type, msg->request_size, and msg->request_data should all be
188 * filled in. If desired, msg->flags can be set.
189 *
190 * If a response is expected, msg->response_size should be set, and
191 * msg->response_data should point to a buffer with enough space. On exit
192 * msg->response_data will be filled.
193 *
194 * Return: number of bytes received or negative error code on failure.
195 */
wilco_ec_mailbox(struct wilco_ec_device * ec,struct wilco_ec_message * msg)196 int wilco_ec_mailbox(struct wilco_ec_device *ec, struct wilco_ec_message *msg)
197 {
198 struct wilco_ec_request *rq;
199 int ret;
200
201 dev_dbg(ec->dev, "type=%04x flags=%02x rslen=%zu rqlen=%zu\n",
202 msg->type, msg->flags, msg->response_size, msg->request_size);
203
204 mutex_lock(&ec->mailbox_lock);
205 /* Prepare request packet */
206 rq = ec->data_buffer;
207 wilco_ec_prepare(msg, rq);
208
209 ret = wilco_ec_transfer(ec, msg, rq);
210 mutex_unlock(&ec->mailbox_lock);
211
212 return ret;
213
214 }
215 EXPORT_SYMBOL_GPL(wilco_ec_mailbox);
216