在 2013-02-15五的 20:16 -0800，Simon Glass写道：

Use the key-matrix layer to interpret key scan information from the EC
and inject input based on the FDT-supplied key map. This driver registers
itself with the ChromeOS EC driver to perform communications.

[snip ...]

+/*
+ * Returns true when there is at least one combination of pressed keys that
+ * results in ghosting.
+ */
+static bool cros_ec_keyb_has_ghosting(struct cros_ec_keyb *ckdev, uint8_t *buf)
+{
+	int row;
+
+	/*
+	 * Ghosting happens if for any pressed key X there are other keys
+	 * pressed both in the same row and column of X as, for instance,
+	 * in the following diagram:
+	 *
+	 * . . Y . g .
+	 * . . . . . .
+	 * . . . . . .
+	 * . . X . Z .
+	 *
+	 * In this case only X, Y, and Z are pressed, but g appears to be
+	 * pressed too (see Wikipedia).
+	 *
+	 * We can detect ghosting in a single pass (*) over the keyboard state
+	 * by maintaining two arrays.  pressed_in_row counts how many pressed
+	 * keys we have found in a row.  row_has_teeth is true if any of the
+	 * pressed keys for this row has other pressed keys in its column.  If
+	 * at any point of the scan we find that a row has multiple pressed
+	 * keys, and at least one of them is at the intersection with a column
+	 * with multiple pressed keys, we're sure there is ghosting.
+	 * Conversely, if there is ghosting, we will detect such situation for
+	 * at least one key during the pass.
+	 *
+	 * (*) This looks linear in the number of keys, but it's not.  We can
+	 * cheat because the number of rows is small.
+	 */
+	for (row = 0; row < ckdev->rows; row++) {
+		if (cros_ec_keyb_row_has_ghosting(ckdev, buf, row))
+			return true;
+	}
+
+	return false;
+}

are you sure your EC's firmware did not do ghost-key detection?
or, did you test ghost-key with/without your own ghost-key detection?
as far as I know, ghost-key should be take care either by keyboard
designer or firmware.

+
+/*
+ * Compares the new keyboard state to the old one and produces key
+ * press/release events accordingly.  The keyboard state is 13 bytes (one byte
+ * per column)
+ */
+static void cros_ec_keyb_process(struct cros_ec_keyb *ckdev,
+			 uint8_t *kb_state, int len)
+{
+	int col, row;
+	int new_state;
+	int num_cols;
+
+	num_cols = len;
+
+	if (ckdev->ghost_filter && cros_ec_keyb_has_ghosting(ckdev, kb_state)) {
+		/*
+		 * Simple-minded solution: ignore this state. The obvious
+		 * improvement is to only ignore changes to keys involved in
+		 * the ghosting, but process the other changes.
+		 */
+		dev_dbg(ckdev->dev, "ghosting found\n");
+		return;
+	}
+
+	for (col = 0; col < ckdev->cols; col++) {
+		for (row = 0; row < ckdev->rows; row++) {
+			int code = MATRIX_SCAN_CODE(row, col, ckdev->row_shift);
+
+			new_state = kb_state[col] & (1 << row);
+			if (!!new_state != test_bit(code, ckdev->idev->key)) {
+				dev_dbg(ckdev->dev,
+					"changed: [r%d c%d]: byte %02x\n",
+					row, col, new_state);
+
+				input_report_key(ckdev->idev, code, new_state);
+			}
+		}
+	}
+	input_sync(ckdev->idev);
+}
+
+static int cros_ec_keyb_open(struct input_dev *dev)
+{
+	struct cros_ec_keyb *ckdev = input_get_drvdata(dev);
+
+	return blocking_notifier_chain_register(&ckdev->ec->event_notifier,
+						&ckdev->notifier);
+}
+
+static void cros_ec_keyb_close(struct input_dev *dev)
+{
+	struct cros_ec_keyb *ckdev = input_get_drvdata(dev);
+
+	blocking_notifier_chain_unregister(&ckdev->ec->event_notifier,
+					   &ckdev->notifier);
+}
+
+static int cros_ec_keyb_get_state(struct cros_ec_keyb *ckdev, uint8_t *kb_state)
+{
+	return ckdev->ec->command_recv(ckdev->ec, EC_CMD_MKBP_STATE,
+					  kb_state, ckdev->cols);
+}
+
+static int cros_ec_keyb_work(struct notifier_block *nb,
+		     unsigned long state, void *_notify)
+{
+	int ret;
+	struct cros_ec_keyb *ckdev = container_of(nb, struct cros_ec_keyb,
+						    notifier);
+	uint8_t kb_state[ckdev->cols];
+
+	ret = cros_ec_keyb_get_state(ckdev, kb_state);
+	if (ret >= 0)
+		cros_ec_keyb_process(ckdev, kb_state, ret);
+
+	return NOTIFY_DONE;
+}
+
+/* Clear any keys in the buffer */
+static void cros_ec_keyb_clear_keyboard(struct cros_ec_keyb *ckdev)
+{
+	uint8_t old_state[ckdev->cols];
+	uint8_t new_state[ckdev->cols];
+	unsigned long duration;
+	int i, ret;
+
+	/*
+	 * Keep reading until we see that the scan state does not change.
+	 * That indicates that we are done.
+	 *
+	 * Assume that the EC keyscan buffer is at most 32 deep.
+	 */
+	duration = jiffies;
+	ret = cros_ec_keyb_get_state(ckdev, new_state);
+	for (i = 1; !ret && i < 32; i++) {
+		memcpy(old_state, new_state, sizeof(old_state));
+		ret = cros_ec_keyb_get_state(ckdev, new_state);
+		if (0 == memcmp(old_state, new_state, sizeof(old_state)))
+			break;
+	}
+	duration = jiffies - duration;
+	dev_info(ckdev->dev, "Discarded %d keyscan(s) in %dus\n", i,
+		jiffies_to_usecs(duration));
+}
+
+static int cros_ec_keyb_probe(struct platform_device *pdev)
+{
+	struct cros_ec_device *ec = dev_get_drvdata(pdev->dev.parent);
+	struct device *dev = ec->dev;
+	struct cros_ec_keyb *ckdev = NULL;
+	struct input_dev *idev = NULL;
+	struct device_node *np;
+	int err;
+
+	np = pdev->dev.of_node;
+	if (!np)
+		return -ENODEV;
+
+	ckdev = kzalloc(sizeof(*ckdev), GFP_KERNEL);
+	if (!ckdev) {
+		dev_err(dev, "cannot allocate memory for ckdev\n");
+		return -ENOMEM;
+	}
+	err = matrix_keypad_parse_of_params(&pdev->dev, &ckdev->rows,
+					    &ckdev->cols);
+	if (err)
+		goto fail_alloc_dev;
+
+	idev = input_allocate_device();
+	if (!idev) {
+		err = -ENOMEM;
+		dev_err(dev, "cannot allocate memory for input device\n");
+		goto fail_alloc_dev;
+	}
+
+	ckdev->ec = ec;
+	ckdev->notifier.notifier_call = cros_ec_keyb_work;
+	ckdev->dev = dev;
+	dev_set_drvdata(&pdev->dev, ckdev);
+
+	idev->name = ec->get_name(ec);
+	idev->phys = ec->get_phys_name(ec);
+	__set_bit(EV_REP, idev->evbit);
+
+	idev->id.bustype = BUS_VIRTUAL;
+	idev->id.version = 1;
+	idev->id.product = 0;
+	idev->dev.parent = &pdev->dev;
+	idev->open = cros_ec_keyb_open;
+	idev->close = cros_ec_keyb_close;
+
+	ckdev->ghost_filter = of_property_read_bool(np,
+					"google,needs-ghost-filter");
+
+	err = matrix_keypad_build_keymap(NULL, NULL, ckdev->rows, ckdev->cols,
+					 NULL, idev);
+	if (err) {
+		dev_err(dev, "cannot build key matrix\n");
+		goto fail_matrix;
+	}
+
+	ckdev->row_shift = get_count_order(ckdev->cols);
+
+	input_set_capability(idev, EV_MSC, MSC_SCAN);
+	input_set_drvdata(idev, ckdev);
+	ckdev->idev = idev;
+	err = input_register_device(ckdev->idev);
+	if (err) {
+		dev_err(dev, "cannot register input device\n");
+		goto fail_register;
+	}
+
+	return 0;
+
+fail_register:
+	kfree(idev->keycode);
+fail_matrix:
+	input_free_device(idev);
+fail_alloc_dev:
+	kfree(ckdev);
+	return err;
+}
+
+static int cros_ec_keyb_remove(struct platform_device *pdev)
+{
+	struct cros_ec_keyb *ckdev = platform_get_drvdata(pdev);
+	struct input_dev *idev = ckdev->idev;
+
+	input_unregister_device(idev);
+	kfree(ckdev);
+
+	return 0;
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int cros_ec_keyb_resume(struct device *dev)
+{
+	struct cros_ec_keyb *ckdev = dev_get_drvdata(dev);
+
+	/*
+	 * When the EC is not a wake source, then it could not have caused the
+	 * resume, so we clear the EC's key scan buffer. If the EC was a
+	 * wake source (e.g. the lid is open and the user might press a key to
+	 * wake) then the key scan buffer should be preserved.
+	 */
+	if (ckdev->ec->was_wake_device)
+		cros_ec_keyb_clear_keyboard(ckdev);
+
+	return 0;
+}
+
+#endif
+
+static SIMPLE_DEV_PM_OPS(cros_ec_keyb_pm_ops, NULL, cros_ec_keyb_resume);
+
+static struct platform_driver cros_ec_keyb_driver = {
+	.probe = cros_ec_keyb_probe,
+	.remove = cros_ec_keyb_remove,
+	.driver = {
+		.name = "cros-ec-keyb",
+		.pm	= &cros_ec_keyb_pm_ops,
+	},
+};
+
+module_platform_driver(cros_ec_keyb_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("ChromeOS EC keyboard driver");
+MODULE_ALIAS("platform:cros-ec-keyb");

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