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Commit 017f14e8 authored by Todd Broch's avatar Todd Broch Committed by Dmitry Torokhov
Browse files

Input: cros_ec_keyb - optimize ghosting algorithm 



Previous algorithm was a bit conservative and complicating with respect to
identifying key ghosting.  This CL uses the bitops hamming weight function
(hweight8) to count the number of matching rows for colM & colN.  If that
number is > 1 ghosting is present.

Additionally it removes NULL keys and our one virtual keypress KEY_BATTERY
from consideration as these inputs are never physical keypresses.

Signed-off-by: default avatarTodd Broch <tbroch@chromium.org>
Reviewed-by: default avatarVincent Palatin <vpalatin@chromium.org>
Reviewed-by: default avatarLuigi Semenzato <semenzato@chromium.org>
Tested-by: default avatarAndreas Färber <afaerber@suse.de>
Signed-off-by: default avatarJavier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: default avatarDmitry Torokhov <dmitry.torokhov@gmail.com>
parent 516d5f8b

drivers/input/keyboard/cros_ec_keyb.c

+49 −43
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ 
 */



#include <linux/module.h>

#include <linux/bitops.h>

#include <linux/i2c.h>

#include <linux/input.h>

#include <linux/interrupt.h>
@@ -38,6 +39,7 @@ 
 * @row_shift: log2 or number of rows, rounded up

 * @keymap_data: Matrix keymap data used to convert to keyscan values

 * @ghost_filter: true to enable the matrix key-ghosting filter

 * @valid_keys: bitmap of existing keys for each matrix column

 * @old_kb_state: bitmap of keys pressed last scan

 * @dev: Device pointer

 * @idev: Input device
@@ -49,6 +51,7 @@ struct cros_ec_keyb { 
	int row_shift;

	const struct matrix_keymap_data *keymap_data;

	bool ghost_filter;

	uint8_t *valid_keys;

	uint8_t *old_kb_state;



	struct device *dev;
@@ -57,39 +60,15 @@ struct cros_ec_keyb { 
};





static bool cros_ec_keyb_row_has_ghosting(struct cros_ec_keyb *ckdev,

					  uint8_t *buf, int row)

{

	int pressed_in_row = 0;

	int row_has_teeth = 0;

	int col, mask;



	mask = 1 << row;

	for (col = 0; col < ckdev->cols; col++) {

		if (buf[col] & mask) {

			pressed_in_row++;

			row_has_teeth |= buf[col] & ~mask;

			if (pressed_in_row > 1 && row_has_teeth) {

				/* ghosting */

				dev_dbg(ckdev->dev,

					"ghost found at: r%d c%d, pressed %d, teeth 0x%x\n",

					row, col, pressed_in_row,

					row_has_teeth);

				return true;

			}

		}

	}



	return false;

}



/*

 * 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;

	int col1, col2, buf1, buf2;

	struct device *dev = ckdev->dev;

	uint8_t *valid_keys = ckdev->valid_keys;



	/*

	 * Ghosting happens if for any pressed key X there are other keys
@@ -103,27 +82,23 @@ static bool cros_ec_keyb_has_ghosting(struct cros_ec_keyb *ckdev, uint8_t *buf) 
	 *

	 * 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))

	for (col1 = 0; col1 < ckdev->cols; col1++) {

		buf1 = buf[col1] & valid_keys[col1];

		for (col2 = col1 + 1; col2 < ckdev->cols; col2++) {

			buf2 = buf[col2] & valid_keys[col2];

			if (hweight8(buf1 & buf2) > 1) {

				dev_dbg(dev, "ghost found at: B[%02d]:0x%02x & B[%02d]:0x%02x",

					col1, buf1, col2, buf2);

				return true;

			}

		}

	}



	return false;

}





/*

 * Compares the new keyboard state to the old one and produces key

 * press/release events accordingly.  The keyboard state is 13 bytes (one byte
@@ -222,6 +197,30 @@ static void cros_ec_keyb_close(struct input_dev *dev) 
	free_irq(ec->irq, ckdev);

}



/*

 * Walks keycodes flipping bit in buffer COLUMNS deep where bit is ROW.  Used by

 * ghosting logic to ignore NULL or virtual keys.

 */

static void cros_ec_keyb_compute_valid_keys(struct cros_ec_keyb *ckdev)

{

	int row, col;

	int row_shift = ckdev->row_shift;

	unsigned short *keymap = ckdev->idev->keycode;

	unsigned short code;



	BUG_ON(ckdev->idev->keycodesize != sizeof(*keymap));



	for (col = 0; col < ckdev->cols; col++) {

		for (row = 0; row < ckdev->rows; row++) {

			code = keymap[MATRIX_SCAN_CODE(row, col, row_shift)];

			if (code && (code != KEY_BATTERY))

				ckdev->valid_keys[col] |= 1 << row;

		}

		dev_dbg(ckdev->dev, "valid_keys[%02d] = 0x%02x\n",

			col, ckdev->valid_keys[col]);

	}

}



static int cros_ec_keyb_probe(struct platform_device *pdev)

{

	struct cros_ec_device *ec = dev_get_drvdata(pdev->dev.parent);
@@ -242,6 +241,11 @@ static int cros_ec_keyb_probe(struct platform_device *pdev) 
					    &ckdev->cols);

	if (err)

		return err;



	ckdev->valid_keys = devm_kzalloc(&pdev->dev, ckdev->cols, GFP_KERNEL);

	if (!ckdev->valid_keys)

		return -ENOMEM;



	ckdev->old_kb_state = devm_kzalloc(&pdev->dev, ckdev->cols, GFP_KERNEL);

	if (!ckdev->old_kb_state)

		return -ENOMEM;
@@ -285,6 +289,8 @@ static int cros_ec_keyb_probe(struct platform_device *pdev) 
	input_set_capability(idev, EV_MSC, MSC_SCAN);

	input_set_drvdata(idev, ckdev);

	ckdev->idev = idev;

	cros_ec_keyb_compute_valid_keys(ckdev);



	err = input_register_device(ckdev->idev);

	if (err) {

		dev_err(dev, "cannot register input device\n");