cros_ec: Support keyboard scanning with EC_CMD_GET_NEXT_EVENT

The cros_ec_keyb driver currently uses EC_CMD_MKBP_STATE to scan the
keyboard, but this host command was superseded by EC_CMD_GET_NEXT_EVENT
and unavailable on more recent devices (including gru-kevin), as it was
removed in cros-ec commit 87a071941b89 ("mkbp: Add support for buttons
and switches.") dated 2016-07-06.

The EC_CMD_GET_NEXT_EVENT has been available since cros-ec commit
d1ed75815efe ("MKBP event signalling implementation") dated 2014-10-20,
but it looks like it isn't included in firmware-* branches for at least
link, nyan-big, samus, snow, spring, panther and peach-pit which have
defconfigs in U-Boot. So this patch falls back to the old method if the
EC doesn't recognize the newer command.

The implementation is mostly adapted from Depthcharge commit
f88af26b44fc ("cros_ec: Change keyboard scanning method.").

On a gru-kevin, the current driver before this patch fails to read the
pressed keys with:

    out: cmd=0x60: 03 9d 60 00 00 00 00 00
    in-header: 03 fc 01 00 00 00 00 00
    in-data:
    ec_command_inptr: len=-1, din=0000000000000000
    check_for_keys: keyboard scan failed

However the keyboard works fine with the newer command:

    out: cmd=0x67: 03 96 67 00 00 00 00 00
    in-header: 03 ef 00 00 0e 00 00 00
    in-data: 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    ec_command_inptr: len=14, din=00000000f412df30
    key_matrix_decode: num_keys = 0
      0 valid keycodes found
    out: cmd=0x67: 03 96 67 00 00 00 00 00
    in-header: 03 df 00 00 0e 00 00 00
    in-data: 00 00 00 00 00 00 00 00 00 00 00 00 10 00
    ec_command_inptr: len=14, din=00000000f412df30
    key_matrix_decode: num_keys = 1
      valid=1, row=4, col=11
        keycode=28
      1 valid keycodes found
     {0d}

Signed-off-by: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

drivers/input/cros_ec_keyb.c

@@ -47,15 +47,35 @@ static int check_for_keys(struct udevice *dev, struct key_matrix_key *keys,
 	struct key_matrix_key *key;
 	static struct mbkp_keyscan last_scan;
 	static bool last_scan_valid;
-	struct mbkp_keyscan scan;
+	struct ec_response_get_next_event event;
+	struct mbkp_keyscan *scan = (struct mbkp_keyscan *)
+				    &event.data.key_matrix;
 	unsigned int row, col, bit, data;
 	int num_keys;
+	int ret;
 
-	if (cros_ec_scan_keyboard(dev->parent, &scan)) {
+	/* Get pending MKBP event. It may not be a key matrix event. */
+	do {
+		ret = cros_ec_get_next_event(dev->parent, &event);
+		/* The EC has no events for us at this time. */
+		if (ret == -EC_RES_UNAVAILABLE)
+			return -EIO;
+		else if (ret)
+			break;
+	} while (event.event_type != EC_MKBP_EVENT_KEY_MATRIX);
+
+	/* Try the old command if the EC doesn't support the above. */
+	if (ret == -EC_RES_INVALID_COMMAND) {
+		if (cros_ec_scan_keyboard(dev->parent, scan)) {
 			debug("%s: keyboard scan failed\n", __func__);
 			return -EIO;
 		}
-	*samep = last_scan_valid && !memcmp(&last_scan, &scan, sizeof(scan));
+	} else if (ret) {
+		debug("%s: Error getting next MKBP event. (%d)\n",
+		      __func__, ret);
+		return -EIO;
+	}
+	*samep = last_scan_valid && !memcmp(&last_scan, scan, sizeof(*scan));
 
 	/*
 	 * This is a bit odd. The EC has no way to tell us that it has run
@@ -64,14 +84,14 @@ static int check_for_keys(struct udevice *dev, struct key_matrix_key *keys,
 	 * that this scan is the same as the last.
 	 */
 	last_scan_valid = true;
-	memcpy(&last_scan, &scan, sizeof(last_scan));
+	memcpy(&last_scan, scan, sizeof(last_scan));
 
 	for (col = num_keys = bit = 0; col < priv->matrix.num_cols;
 			col++) {
 		for (row = 0; row < priv->matrix.num_rows; row++) {
 			unsigned int mask = 1 << (bit & 7);
 
-			data = scan.data[bit / 8];
+			data = scan->data[bit / 8];
 			if ((data & mask) && num_keys < max_count) {
 				key = keys + num_keys++;
 				key->row = row;

drivers/misc/cros_ec.c

@@ -415,6 +415,21 @@ int cros_ec_scan_keyboard(struct udevice *dev, struct mbkp_keyscan *scan)
 	return 0;
 }
 
+int cros_ec_get_next_event(struct udevice *dev,
+			   struct ec_response_get_next_event *event)
+{
+	int ret;
+
+	ret = ec_command(dev, EC_CMD_GET_NEXT_EVENT, 0, NULL, 0,
+			 event, sizeof(*event));
+	if (ret < 0)
+		return ret;
+	else if (ret != sizeof(*event))
+		return -EC_RES_INVALID_RESPONSE;
+
+	return 0;
+}
+
 int cros_ec_read_id(struct udevice *dev, char *id, int maxlen)
 {
 	struct ec_response_get_version *r;

include/cros_ec.h

@@ -82,6 +82,17 @@ int cros_ec_read_id(struct udevice *dev, char *id, int maxlen);
  */
 int cros_ec_scan_keyboard(struct udevice *dev, struct mbkp_keyscan *scan);
 
+/**
+ * Get the next pending MKBP event from the ChromeOS EC device.
+ *
+ * Send a message requesting the next event and return the result.
+ *
+ * @param event		Place to put the event.
+ * @return 0 if ok, <0 on error.
+ */
+int cros_ec_get_next_event(struct udevice *dev,
+			   struct ec_response_get_next_event *event);
+
 /**
  * Read which image is currently running on the CROS-EC device.
  *