platform/chrome: wilco_ec: Standardize mailbox interface

The current API for the wilco EC mailbox interface is bad.

It assumes that most messages sent to the EC follow a similar structure,
with a command byte in MBOX[0], followed by a junk byte, followed by
actual data. This doesn't happen in several cases, such as setting the
RTC time, using the raw debugfs interface, and reading or writing
properties such as the Peak Shift policy (this last to be submitted soon).

Similarly for the response message from the EC, the current interface
assumes that the first byte of data is always 0, and the second byte
is unused. However, in both setting and getting the RTC time, in the
debugfs interface, and for reading and writing properties, this isn't
true.

The current way to resolve this is to use WILCO_EC_FLAG_RAW* flags to
specify when and when not to skip these initial bytes in the sent and
received message. They are confusing and used so much that they are
normal, and not exceptions. In addition, the first byte of
response in the debugfs interface is still always skipped, which is
weird, since this raw interface should be giving the entire result.

Additionally, sent messages assume the first byte is a command, and so
struct wilco_ec_message contains the "command" field. In setting or
getting properties however, the first byte is not a command, and so this
field has to be filled with a byte that isn't actually a command. This
is again inconsistent.

wilco_ec_message contains a result field as well, copied from
wilco_ec_response->result. The message result field should be removed:
if the message fails, the cause is already logged, and the callers are
alerted. They will never care about the actual state of the result flag.

These flags and different cases make the wilco_ec_transfer() function,
used in wilco_ec_mailbox(), really gross, dealing with a bunch of
different cases. It's difficult to figure out what it is doing.

Finally, making these assumptions about the structure of a message make
it so that the messages do not correspond well with the specification
for the EC's mailbox interface. For instance, this interface
specification may say that MBOX[9] in the received message contains
some information, but the calling code needs to remember that the first
byte of response is always skipped, and because it didn't set the
RESPONSE_RAW flag, the next byte is also skipped, so this information
is actually contained within wilco_ec_message->response_data[7]. This
makes it difficult to maintain this code in the future.

To fix these problems this patch standardizes the mailbox interface by:
- Removing the WILCO_EC_FLAG_RAW* flags
- Removing the command and reserved_raw bytes from wilco_ec_request
- Removing the mbox0 byte from wilco_ec_response
- Simplifying wilco_ec_transfer() because of these changes
- Gives the callers of wilco_ec_mailbox() the responsibility of exactly
and consistently defining the structure of the mailbox request and
response
- Removing command and result from wilco_ec_message.

This results in the reduction of total code, and makes it much more
maintainable and understandable.

Signed-off-by: Nick Crews <[e-mail]>
Acked-by: Alexandre Belloni <[e-mail]>
Signed-off-by: Enric Balletbo i Serra <[e-mail]>

Documentation/ABI/testing/debugfs-wilco-ec

···
 Description:
 		Write and read raw mailbox commands to the EC.
 
-		For writing:
-		Bytes 0-1 indicate the message type:
-			00 F0 = Execute Legacy Command
-			00 F2 = Read/Write NVRAM Property
-		Byte 2 provides the command code
-		Bytes 3+ consist of the data passed in the request
+		You can write a hexadecimal sentence to raw, and that series of
+		bytes will be sent to the EC. Then, you can read the bytes of
+		response by reading from raw.
 
-		At least three bytes are required, for the msg type and command,
-		with additional bytes optional for additional data.
+		For writing, bytes 0-1 indicate the message type, one of enum
+		wilco_ec_msg_type. Byte 2+ consist of the data passed in the
+		request, starting at MBOX[0]
+
+		At least three bytes are required for writing, two for the type
+		and at least a single byte of data. Only the first
+		EC_MAILBOX_DATA_SIZE bytes of MBOX will be used.
 
 		Example:
 		// Request EC info type 3 (EC firmware build date)
-		$ echo 00 f0 38 00 03 00 > raw
+		// Corresponds with sending type 0x00f0 with
+		// MBOX = [38, 00, 03, 00]
+		$ echo 00 f0 38 00 03 00 > /sys/kernel/debug/wilco_ec/raw
 		// View the result. The decoded ASCII result "12/21/18" is
 		// included after the raw hex.
-		$ cat raw
-		00 31 32 2f 32 31 2f 31 38 00 38 00 01 00 2f 00  .12/21/18.8...
+		// Corresponds with MBOX = [00, 00, 31, 32, 2f, 32, 31, 38, ...]
+		$ cat /sys/kernel/debug/wilco_ec/raw
+		00 00 31 32 2f 32 31 2f 31 38 00 38 00 01 00 2f 00  ..12/21/18.8...
+
+		Note that the first 32 bytes of the received MBOX[] will be
+		printed, even if some of the data is junk. It is up to you to
+		know how many of the first bytes of data are the actual
+		response.

drivers/platform/chrome/wilco_ec/debugfs.c

···
  *
  * Copyright 2019 Google LLC
  *
- * There is only one attribute used for debugging, called raw.
- * You can write a hexadecimal sentence to raw, and that series of bytes
- * will be sent to the EC. Then, you can read the bytes of response
- * by reading from raw.
- *
- * For writing:
- * Bytes 0-1 indicate the message type:
- *         00 F0 = Execute Legacy Command
- *         00 F2 = Read/Write NVRAM Property
- * Byte 2 provides the command code
- * Bytes 3+ consist of the data passed in the request
- *
- * When referencing the EC interface spec, byte 2 corresponds to MBOX[0],
- * byte 3 corresponds to MBOX[1], etc.
- *
- * At least three bytes are required, for the msg type and command,
- * with additional bytes optional for additional data.
- *
- * Example:
- * // Request EC info type 3 (EC firmware build date)
- * $ echo 00 f0 38 00 03 00 > raw
- * // View the result. The decoded ASCII result "12/21/18" is
- * // included after the raw hex.
- * $ cat raw
- * 00 31 32 2f 32 31 2f 31 38 00 38 00 01 00 2f 00  .12/21/18.8...
+ * See Documentation/ABI/testing/debugfs-wilco-ec for usage.
  */
 
 #include <linux/ctype.h>
···
 	ret = parse_hex_sentence(buf, kcount, request_data, TYPE_AND_DATA_SIZE);
 	if (ret < 0)
 		return ret;
-	/* Need at least two bytes for message type and one for command */
+	/* Need at least two bytes for message type and one byte of data */
 	if (ret < 3)
 		return -EINVAL;
 
-	/* Clear response data buffer */
-	memset(debug_info->raw_data, '\0', EC_MAILBOX_DATA_SIZE_EXTENDED);
-
 	msg.type = request_data[0] << 8 | request_data[1];
-	msg.flags = WILCO_EC_FLAG_RAW;
-	msg.command = request_data[2];
-	msg.request_data = ret > 3 ? request_data + 3 : 0;
-	msg.request_size = ret - 3;
+	msg.flags = 0;
+	msg.request_data = request_data + 2;
+	msg.request_size = ret - 2;
+	memset(debug_info->raw_data, 0, sizeof(debug_info->raw_data));
 	msg.response_data = debug_info->raw_data;
 	msg.response_size = EC_MAILBOX_DATA_SIZE;
 
···
 		fmt_len = hex_dump_to_buffer(debug_info->raw_data,
 					     debug_info->response_size,
 					     16, 1, debug_info->formatted_data,
-					     FORMATTED_BUFFER_SIZE, true);
+					     sizeof(debug_info->formatted_data),
+					     true);
 		/* Only return response the first time it is read */
 		debug_info->response_size = 0;
 	}

drivers/platform/chrome/wilco_ec/mailbox.c

···
 			     struct wilco_ec_request *rq)
 {
 	memset(rq, 0, sizeof(*rq));
-
-	/* Handle messages without trimming bytes from the request */
-	if (msg->request_size && msg->flags & WILCO_EC_FLAG_RAW_REQUEST) {
-		rq->reserved_raw = *(u8 *)msg->request_data;
-		msg->request_size--;
-		memmove(msg->request_data, msg->request_data + 1,
-			msg->request_size);
-	}
-
-	/* Fill in request packet */
 	rq->struct_version = EC_MAILBOX_PROTO_VERSION;
 	rq->mailbox_id = msg->type;
 	rq->mailbox_version = EC_MAILBOX_VERSION;
-	rq->data_size = msg->request_size + EC_MAILBOX_DATA_EXTRA;
-	rq->command = msg->command;
+	rq->data_size = msg->request_size;
 
 	/* Checksum header and data */
 	rq->checksum = wilco_ec_checksum(rq, sizeof(*rq));
···
 		return -EIO;
 	}
 
+	/*
+	 * The EC always returns either EC_MAILBOX_DATA_SIZE or
+	 * EC_MAILBOX_DATA_SIZE_EXTENDED bytes of data, so we need to
+	 * calculate the checksum on **all** of this data, even if we
+	 * won't use all of it.
+	 */
 	if (msg->flags & WILCO_EC_FLAG_EXTENDED_DATA)
 		size = EC_MAILBOX_DATA_SIZE_EXTENDED;
 	else
···
 		return -EBADMSG;
 	}
 
-	/* Check that the EC reported success */
-	msg->result = rs->result;
-	if (msg->result) {
-		dev_dbg(ec->dev, "bad response: 0x%02x\n", msg->result);
+	if (rs->result) {
+		dev_dbg(ec->dev, "EC reported failure: 0x%02x\n", rs->result);
 		return -EBADMSG;
 	}
 
-	/* Check the returned data size, skipping the header */
 	if (rs->data_size != size) {
 		dev_dbg(ec->dev, "unexpected packet size (%u != %zu)",
 			rs->data_size, size);
 		return -EMSGSIZE;
 	}
 
-	/* Skip 1 response data byte unless specified */
-	size = (msg->flags & WILCO_EC_FLAG_RAW_RESPONSE) ? 0 : 1;
-	if ((ssize_t) rs->data_size - size < msg->response_size) {
-		dev_dbg(ec->dev, "response data too short (%zd < %zu)",
-			(ssize_t) rs->data_size - size, msg->response_size);
+	if (rs->data_size < msg->response_size) {
+		dev_dbg(ec->dev, "EC didn't return enough data (%u < %zu)",
+			rs->data_size, msg->response_size);
 		return -EMSGSIZE;
 	}
 
-	/* Ignore response data bytes as requested */
-	memcpy(msg->response_data, rs->data + size, msg->response_size);
+	memcpy(msg->response_data, rs->data, msg->response_size);
 
-	/* Return actual amount of data received */
-	return msg->response_size;
+	return rs->data_size;
 }
 
 /**
···
  * @ec: EC device.
  * @msg: EC message data for request and response.
  *
- * On entry msg->type, msg->flags, msg->command, msg->request_size,
- * msg->response_size, and msg->request_data should all be filled in.
+ * On entry msg->type, msg->request_size, and msg->request_data should all be
+ * filled in. If desired, msg->flags can be set.
  *
- * On exit msg->result and msg->response_data will be filled.
+ * If a response is expected, msg->response_size should be set, and
+ * msg->response_data should point to a buffer with enough space. On exit
+ * msg->response_data will be filled.
  *
  * Return: number of bytes received or negative error code on failure.
  */
···
 	struct wilco_ec_request *rq;
 	int ret;
 
-	dev_dbg(ec->dev, "cmd=%02x type=%04x flags=%02x rslen=%zu rqlen=%zu\n",
-		msg->command, msg->type, msg->flags, msg->response_size,
-		msg->request_size);
+	dev_dbg(ec->dev, "type=%04x flags=%02x rslen=%zu rqlen=%zu\n",
+		msg->type, msg->flags, msg->response_size, msg->request_size);
 
 	mutex_lock(&ec->mailbox_lock);
 	/* Prepare request packet */

drivers/rtc/rtc-wilco-ec.c

···
 #define EC_CMOS_TOD_WRITE		0x02
 #define EC_CMOS_TOD_READ		0x08
 
+/* Message sent to the EC to request the current time. */
+struct ec_rtc_read_request {
+	u8 command;
+	u8 reserved;
+	u8 param;
+} __packed;
+static struct ec_rtc_read_request read_rq = {
+	.command = EC_COMMAND_CMOS,
+	.param = EC_CMOS_TOD_READ,
+};
+
 /**
- * struct ec_rtc_read - Format of RTC returned by EC.
+ * struct ec_rtc_read_response - Format of RTC returned by EC.
+ * @reserved: Unused byte
  * @second: Second value (0..59)
  * @minute: Minute value (0..59)
  * @hour: Hour value (0..23)
···
  *
  * All values are presented in binary (not BCD).
  */
-struct ec_rtc_read {
+struct ec_rtc_read_response {
+	u8 reserved;
 	u8 second;
 	u8 minute;
 	u8 hour;
···
 } __packed;
 
 /**
- * struct ec_rtc_write - Format of RTC sent to the EC.
- * @param: EC_CMOS_TOD_WRITE
+ * struct ec_rtc_write_request - Format of RTC sent to the EC.
+ * @command: Always EC_COMMAND_CMOS
+ * @reserved: Unused byte
+ * @param: Always EC_CMOS_TOD_WRITE
  * @century: Century value (full year / 100)
  * @year: Year value (full year % 100)
  * @month: Month value (1..12)
···
  *
  * All values are presented in BCD.
  */
-struct ec_rtc_write {
+struct ec_rtc_write_request {
+	u8 command;
+	u8 reserved;
 	u8 param;
 	u8 century;
 	u8 year;
···
 static int wilco_ec_rtc_read(struct device *dev, struct rtc_time *tm)
 {
 	struct wilco_ec_device *ec = dev_get_drvdata(dev->parent);
-	u8 param = EC_CMOS_TOD_READ;
-	struct ec_rtc_read rtc;
-	struct wilco_ec_message msg = {
-		.type = WILCO_EC_MSG_LEGACY,
-		.flags = WILCO_EC_FLAG_RAW_RESPONSE,
-		.command = EC_COMMAND_CMOS,
-		.request_data = &param,
-		.request_size = sizeof(param),
-		.response_data = &rtc,
-		.response_size = sizeof(rtc),
-	};
+	struct ec_rtc_read_response rtc;
+	struct wilco_ec_message msg;
 	int ret;
+
+	memset(&msg, 0, sizeof(msg));
+	msg.type = WILCO_EC_MSG_LEGACY;
+	msg.request_data = &read_rq;
+	msg.request_size = sizeof(read_rq);
+	msg.response_data = &rtc;
+	msg.response_size = sizeof(rtc);
 
 	ret = wilco_ec_mailbox(ec, &msg);
 	if (ret < 0)
···
 static int wilco_ec_rtc_write(struct device *dev, struct rtc_time *tm)
 {
 	struct wilco_ec_device *ec = dev_get_drvdata(dev->parent);
-	struct ec_rtc_write rtc;
-	struct wilco_ec_message msg = {
-		.type = WILCO_EC_MSG_LEGACY,
-		.flags = WILCO_EC_FLAG_RAW_RESPONSE,
-		.command = EC_COMMAND_CMOS,
-		.request_data = &rtc,
-		.request_size = sizeof(rtc),
-	};
+	struct ec_rtc_write_request rtc;
+	struct wilco_ec_message msg;
 	int year = tm->tm_year + 1900;
 	/*
 	 * Convert from 0=Sunday to 0=Saturday for the EC
···
 	int wday = tm->tm_wday == 6 ? 0 : tm->tm_wday + 1;
 	int ret;
 
+	rtc.command	= EC_COMMAND_CMOS;
 	rtc.param	= EC_CMOS_TOD_WRITE;
 	rtc.century	= bin2bcd(year / 100);
 	rtc.year	= bin2bcd(year % 100);
···
 	rtc.minute	= bin2bcd(tm->tm_min);
 	rtc.second	= bin2bcd(tm->tm_sec);
 	rtc.weekday	= bin2bcd(wday);
+
+	memset(&msg, 0, sizeof(msg));
+	msg.type = WILCO_EC_MSG_LEGACY;
+	msg.request_data = &rtc;
+	msg.request_size = sizeof(rtc);
 
 	ret = wilco_ec_mailbox(ec, &msg);
 	if (ret < 0)

include/linux/platform_data/wilco-ec.h

···
 /* Message flags for using the mailbox() interface */
 #define WILCO_EC_FLAG_NO_RESPONSE	BIT(0) /* EC does not respond */
 #define WILCO_EC_FLAG_EXTENDED_DATA	BIT(1) /* EC returns 256 data bytes */
-#define WILCO_EC_FLAG_RAW_REQUEST	BIT(2) /* Do not trim request data */
-#define WILCO_EC_FLAG_RAW_RESPONSE	BIT(3) /* Do not trim response data */
-#define WILCO_EC_FLAG_RAW		(WILCO_EC_FLAG_RAW_REQUEST | \
-					 WILCO_EC_FLAG_RAW_RESPONSE)
 
 /* Normal commands have a maximum 32 bytes of data */
 #define EC_MAILBOX_DATA_SIZE		32
···
  * @mailbox_id: Mailbox identifier, specifies the command set.
  * @mailbox_version: Mailbox interface version %EC_MAILBOX_VERSION
  * @reserved: Set to zero.
- * @data_size: Length of request, data + last 2 bytes of the header.
- * @command: Mailbox command code, unique for each mailbox_id set.
- * @reserved_raw: Set to zero for most commands, but is used by
- *                some command types and for raw commands.
+ * @data_size: Length of following data.
  */
 struct wilco_ec_request {
 	u8 struct_version;
···
 	u8 mailbox_version;
 	u8 reserved;
 	u16 data_size;
-	u8 command;
-	u8 reserved_raw;
 } __packed;
 
 /**
···
  * @result: Result code from the EC.  Non-zero indicates an error.
  * @data_size: Length of the response data buffer.
  * @reserved: Set to zero.
- * @mbox0: EC returned data at offset 0 is unused (always 0) so this byte
- *         is treated as part of the header instead of the data.
  * @data: Response data buffer.  Max size is %EC_MAILBOX_DATA_SIZE_EXTENDED.
  */
 struct wilco_ec_response {
···
 	u16 result;
 	u16 data_size;
 	u8 reserved[2];
-	u8 mbox0;
 	u8 data[0];
 } __packed;
 
···
  * struct wilco_ec_message - Request and response message.
  * @type: Mailbox message type.
  * @flags: Message flags, e.g. %WILCO_EC_FLAG_NO_RESPONSE.
- * @command: Mailbox command code.
- * @result: Result code from the EC.  Non-zero indicates an error.
  * @request_size: Number of bytes to send to the EC.
  * @request_data: Buffer containing the request data.
- * @response_size: Number of bytes expected from the EC.
- *                 This is 32 by default and 256 if the flag
- *                 is set for %WILCO_EC_FLAG_EXTENDED_DATA
+ * @response_size: Number of bytes to read from EC.
  * @response_data: Buffer containing the response data, should be
  *                 response_size bytes and allocated by caller.
  */
 struct wilco_ec_message {
 	enum wilco_ec_msg_type type;
 	u8 flags;
-	u8 command;
-	u8 result;
 	size_t request_size;
 	void *request_data;
 	size_t response_size;