1/*
2 * ChromeOS EC multi-function device (SPI)
3 *
4 * Copyright (C) 2012 Google, Inc
5 *
6 * This software is licensed under the terms of the GNU General Public
7 * License version 2, as published by the Free Software Foundation, and
8 * may be copied, distributed, and modified under those terms.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13 * GNU General Public License for more details.
14 */
15
16#include <linux/delay.h>
17#include <linux/kernel.h>
18#include <linux/module.h>
19#include <linux/mfd/cros_ec.h>
20#include <linux/mfd/cros_ec_commands.h>
21#include <linux/of.h>
22#include <linux/platform_device.h>
23#include <linux/slab.h>
24#include <linux/spi/spi.h>
25
26
27/* The header byte, which follows the preamble */
28#define EC_MSG_HEADER			0xec
29
30/*
31 * Number of EC preamble bytes we read at a time. Since it takes
32 * about 400-500us for the EC to respond there is not a lot of
33 * point in tuning this. If the EC could respond faster then
34 * we could increase this so that might expect the preamble and
35 * message to occur in a single transaction. However, the maximum
36 * SPI transfer size is 256 bytes, so at 5MHz we need a response
37 * time of perhaps <320us (200 bytes / 1600 bits).
38 */
39#define EC_MSG_PREAMBLE_COUNT		32
40
41/*
42 * Allow for a long time for the EC to respond.  We support i2c
43 * tunneling and support fairly long messages for the tunnel (249
44 * bytes long at the moment).  If we're talking to a 100 kHz device
45 * on the other end and need to transfer ~256 bytes, then we need:
46 *  10 us/bit * ~10 bits/byte * ~256 bytes = ~25ms
47 *
48 * We'll wait 4 times that to handle clock stretching and other
49 * paranoia.
50 *
51 * It's pretty unlikely that we'll really see a 249 byte tunnel in
52 * anything other than testing.  If this was more common we might
53 * consider having slow commands like this require a GET_STATUS
54 * wait loop.  The 'flash write' command would be another candidate
55 * for this, clocking in at 2-3ms.
56 */
57#define EC_MSG_DEADLINE_MS		100
58
59/*
60  * Time between raising the SPI chip select (for the end of a
61  * transaction) and dropping it again (for the next transaction).
62  * If we go too fast, the EC will miss the transaction. We know that we
63  * need at least 70 us with the 16 MHz STM32 EC, so go with 200 us to be
64  * safe.
65  */
66#define EC_SPI_RECOVERY_TIME_NS	(200 * 1000)
67
68/*
69 * The EC is unresponsive for a time after a reboot command.  Add a
70 * simple delay to make sure that the bus stays locked.
71 */
72#define EC_REBOOT_DELAY_MS	50
73
74/**
75 * struct cros_ec_spi - information about a SPI-connected EC
76 *
77 * @spi: SPI device we are connected to
78 * @last_transfer_ns: time that we last finished a transfer, or 0 if there
79 *	if no record
80 * @end_of_msg_delay: used to set the delay_usecs on the spi_transfer that
81 *      is sent when we want to turn off CS at the end of a transaction.
82 */
83struct cros_ec_spi {
84	struct spi_device *spi;
85	s64 last_transfer_ns;
86	unsigned int end_of_msg_delay;
87};
88
89static void debug_packet(struct device *dev, const char *name, u8 *ptr,
90			  int len)
91{
92#ifdef DEBUG
93	int i;
94
95	dev_dbg(dev, "%s: ", name);
96	for (i = 0; i < len; i++)
97		pr_cont(" %02x", ptr[i]);
98
99	pr_cont("\n");
100#endif
101}
102
103/**
104 * cros_ec_spi_receive_response - Receive a response from the EC.
105 *
106 * This function has two phases: reading the preamble bytes (since if we read
107 * data from the EC before it is ready to send, we just get preamble) and
108 * reading the actual message.
109 *
110 * The received data is placed into ec_dev->din.
111 *
112 * @ec_dev: ChromeOS EC device
113 * @need_len: Number of message bytes we need to read
114 */
115static int cros_ec_spi_receive_response(struct cros_ec_device *ec_dev,
116					int need_len)
117{
118	struct cros_ec_spi *ec_spi = ec_dev->priv;
119	struct spi_transfer trans;
120	struct spi_message msg;
121	u8 *ptr, *end;
122	int ret;
123	unsigned long deadline;
124	int todo;
125
126	/* Receive data until we see the header byte */
127	deadline = jiffies + msecs_to_jiffies(EC_MSG_DEADLINE_MS);
128	while (true) {
129		unsigned long start_jiffies = jiffies;
130
131		memset(&trans, 0, sizeof(trans));
132		trans.cs_change = 1;
133		trans.rx_buf = ptr = ec_dev->din;
134		trans.len = EC_MSG_PREAMBLE_COUNT;
135
136		spi_message_init(&msg);
137		spi_message_add_tail(&trans, &msg);
138		ret = spi_sync(ec_spi->spi, &msg);
139		if (ret < 0) {
140			dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
141			return ret;
142		}
143
144		for (end = ptr + EC_MSG_PREAMBLE_COUNT; ptr != end; ptr++) {
145			if (*ptr == EC_MSG_HEADER) {
146				dev_dbg(ec_dev->dev, "msg found at %zd\n",
147					ptr - ec_dev->din);
148				break;
149			}
150		}
151		if (ptr != end)
152			break;
153
154		/*
155		 * Use the time at the start of the loop as a timeout.  This
156		 * gives us one last shot at getting the transfer and is useful
157		 * in case we got context switched out for a while.
158		 */
159		if (time_after(start_jiffies, deadline)) {
160			dev_warn(ec_dev->dev, "EC failed to respond in time\n");
161			return -ETIMEDOUT;
162		}
163	}
164
165	/*
166	 * ptr now points to the header byte. Copy any valid data to the
167	 * start of our buffer
168	 */
169	todo = end - ++ptr;
170	BUG_ON(todo < 0 || todo > ec_dev->din_size);
171	todo = min(todo, need_len);
172	memmove(ec_dev->din, ptr, todo);
173	ptr = ec_dev->din + todo;
174	dev_dbg(ec_dev->dev, "need %d, got %d bytes from preamble\n",
175		 need_len, todo);
176	need_len -= todo;
177
178	/* Receive data until we have it all */
179	while (need_len > 0) {
180		/*
181		 * We can't support transfers larger than the SPI FIFO size
182		 * unless we have DMA. We don't have DMA on the ISP SPI ports
183		 * for Exynos. We need a way of asking SPI driver for
184		 * maximum-supported transfer size.
185		 */
186		todo = min(need_len, 256);
187		dev_dbg(ec_dev->dev, "loop, todo=%d, need_len=%d, ptr=%zd\n",
188			todo, need_len, ptr - ec_dev->din);
189
190		memset(&trans, 0, sizeof(trans));
191		trans.cs_change = 1;
192		trans.rx_buf = ptr;
193		trans.len = todo;
194		spi_message_init(&msg);
195		spi_message_add_tail(&trans, &msg);
196
197		/* send command to EC and read answer */
198		BUG_ON((u8 *)trans.rx_buf - ec_dev->din + todo >
199				ec_dev->din_size);
200		ret = spi_sync(ec_spi->spi, &msg);
201		if (ret < 0) {
202			dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
203			return ret;
204		}
205
206		debug_packet(ec_dev->dev, "interim", ptr, todo);
207		ptr += todo;
208		need_len -= todo;
209	}
210
211	dev_dbg(ec_dev->dev, "loop done, ptr=%zd\n", ptr - ec_dev->din);
212
213	return 0;
214}
215
216/**
217 * cros_ec_cmd_xfer_spi - Transfer a message over SPI and receive the reply
218 *
219 * @ec_dev: ChromeOS EC device
220 * @ec_msg: Message to transfer
221 */
222static int cros_ec_cmd_xfer_spi(struct cros_ec_device *ec_dev,
223				struct cros_ec_command *ec_msg)
224{
225	struct cros_ec_spi *ec_spi = ec_dev->priv;
226	struct spi_transfer trans;
227	struct spi_message msg;
228	int i, len;
229	u8 *ptr;
230	int sum;
231	int ret = 0, final_ret;
232
233	len = cros_ec_prepare_tx(ec_dev, ec_msg);
234	dev_dbg(ec_dev->dev, "prepared, len=%d\n", len);
235
236	/* If it's too soon to do another transaction, wait */
237	if (ec_spi->last_transfer_ns) {
238		unsigned long delay;	/* The delay completed so far */
239
240		delay = ktime_get_ns() - ec_spi->last_transfer_ns;
241		if (delay < EC_SPI_RECOVERY_TIME_NS)
242			ndelay(EC_SPI_RECOVERY_TIME_NS - delay);
243	}
244
245	/* Transmit phase - send our message */
246	debug_packet(ec_dev->dev, "out", ec_dev->dout, len);
247	memset(&trans, 0, sizeof(trans));
248	trans.tx_buf = ec_dev->dout;
249	trans.len = len;
250	trans.cs_change = 1;
251	spi_message_init(&msg);
252	spi_message_add_tail(&trans, &msg);
253	ret = spi_sync(ec_spi->spi, &msg);
254
255	/* Get the response */
256	if (!ret) {
257		ret = cros_ec_spi_receive_response(ec_dev,
258				ec_msg->insize + EC_MSG_TX_PROTO_BYTES);
259	} else {
260		dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
261	}
262
263	/*
264	 * Turn off CS, possibly adding a delay to ensure the rising edge
265	 * doesn't come too soon after the end of the data.
266	 */
267	spi_message_init(&msg);
268	memset(&trans, 0, sizeof(trans));
269	trans.delay_usecs = ec_spi->end_of_msg_delay;
270	spi_message_add_tail(&trans, &msg);
271
272	final_ret = spi_sync(ec_spi->spi, &msg);
273	ec_spi->last_transfer_ns = ktime_get_ns();
274	if (!ret)
275		ret = final_ret;
276	if (ret < 0) {
277		dev_err(ec_dev->dev, "spi transfer failed: %d\n", ret);
278		goto exit;
279	}
280
281	ptr = ec_dev->din;
282
283	/* check response error code */
284	ec_msg->result = ptr[0];
285	ret = cros_ec_check_result(ec_dev, ec_msg);
286	if (ret)
287		goto exit;
288
289	len = ptr[1];
290	sum = ptr[0] + ptr[1];
291	if (len > ec_msg->insize) {
292		dev_err(ec_dev->dev, "packet too long (%d bytes, expected %d)",
293			len, ec_msg->insize);
294		ret = -ENOSPC;
295		goto exit;
296	}
297
298	/* copy response packet payload and compute checksum */
299	for (i = 0; i < len; i++) {
300		sum += ptr[i + 2];
301		if (ec_msg->insize)
302			ec_msg->indata[i] = ptr[i + 2];
303	}
304	sum &= 0xff;
305
306	debug_packet(ec_dev->dev, "in", ptr, len + 3);
307
308	if (sum != ptr[len + 2]) {
309		dev_err(ec_dev->dev,
310			"bad packet checksum, expected %02x, got %02x\n",
311			sum, ptr[len + 2]);
312		ret = -EBADMSG;
313		goto exit;
314	}
315
316	ret = len;
317exit:
318	if (ec_msg->command == EC_CMD_REBOOT_EC)
319		msleep(EC_REBOOT_DELAY_MS);
320
321	return ret;
322}
323
324static void cros_ec_spi_dt_probe(struct cros_ec_spi *ec_spi, struct device *dev)
325{
326	struct device_node *np = dev->of_node;
327	u32 val;
328	int ret;
329
330	ret = of_property_read_u32(np, "google,cros-ec-spi-msg-delay", &val);
331	if (!ret)
332		ec_spi->end_of_msg_delay = val;
333}
334
335static int cros_ec_spi_probe(struct spi_device *spi)
336{
337	struct device *dev = &spi->dev;
338	struct cros_ec_device *ec_dev;
339	struct cros_ec_spi *ec_spi;
340	int err;
341
342	spi->bits_per_word = 8;
343	spi->mode = SPI_MODE_0;
344	err = spi_setup(spi);
345	if (err < 0)
346		return err;
347
348	ec_spi = devm_kzalloc(dev, sizeof(*ec_spi), GFP_KERNEL);
349	if (ec_spi == NULL)
350		return -ENOMEM;
351	ec_spi->spi = spi;
352	ec_dev = devm_kzalloc(dev, sizeof(*ec_dev), GFP_KERNEL);
353	if (!ec_dev)
354		return -ENOMEM;
355
356	/* Check for any DT properties */
357	cros_ec_spi_dt_probe(ec_spi, dev);
358
359	spi_set_drvdata(spi, ec_dev);
360	ec_dev->dev = dev;
361	ec_dev->priv = ec_spi;
362	ec_dev->irq = spi->irq;
363	ec_dev->cmd_xfer = cros_ec_cmd_xfer_spi;
364	ec_dev->ec_name = ec_spi->spi->modalias;
365	ec_dev->phys_name = dev_name(&ec_spi->spi->dev);
366	ec_dev->parent = &ec_spi->spi->dev;
367	ec_dev->din_size = EC_MSG_BYTES + EC_MSG_PREAMBLE_COUNT;
368	ec_dev->dout_size = EC_MSG_BYTES;
369
370	err = cros_ec_register(ec_dev);
371	if (err) {
372		dev_err(dev, "cannot register EC\n");
373		return err;
374	}
375
376	device_init_wakeup(&spi->dev, true);
377
378	return 0;
379}
380
381static int cros_ec_spi_remove(struct spi_device *spi)
382{
383	struct cros_ec_device *ec_dev;
384
385	ec_dev = spi_get_drvdata(spi);
386	cros_ec_remove(ec_dev);
387
388	return 0;
389}
390
391#ifdef CONFIG_PM_SLEEP
392static int cros_ec_spi_suspend(struct device *dev)
393{
394	struct cros_ec_device *ec_dev = dev_get_drvdata(dev);
395
396	return cros_ec_suspend(ec_dev);
397}
398
399static int cros_ec_spi_resume(struct device *dev)
400{
401	struct cros_ec_device *ec_dev = dev_get_drvdata(dev);
402
403	return cros_ec_resume(ec_dev);
404}
405#endif
406
407static SIMPLE_DEV_PM_OPS(cros_ec_spi_pm_ops, cros_ec_spi_suspend,
408			 cros_ec_spi_resume);
409
410static const struct spi_device_id cros_ec_spi_id[] = {
411	{ "cros-ec-spi", 0 },
412	{ }
413};
414MODULE_DEVICE_TABLE(spi, cros_ec_spi_id);
415
416static struct spi_driver cros_ec_driver_spi = {
417	.driver	= {
418		.name	= "cros-ec-spi",
419		.owner	= THIS_MODULE,
420		.pm	= &cros_ec_spi_pm_ops,
421	},
422	.probe		= cros_ec_spi_probe,
423	.remove		= cros_ec_spi_remove,
424	.id_table	= cros_ec_spi_id,
425};
426
427module_spi_driver(cros_ec_driver_spi);
428
429MODULE_LICENSE("GPL v2");
430MODULE_DESCRIPTION("ChromeOS EC multi function device (SPI)");
431