Input: tegra-kbc - add ghost key filter

Add ghost key filtering support for the Nvidia Tegra matrix keyboard.

Signed-off-by: Rakesh Iyer <riyer@nvidia.com>
Reviewed-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

arch/arm/mach-tegra/include/mach/kbc.h

@@ -58,5 +58,6 @@ struct tegra_kbc_platform_data {
 
 	bool wakeup;
 	bool use_fn_map;
+	bool use_ghost_filter;
 };
 #endif

drivers/input/keyboard/tegra-kbc.c

@@ -72,6 +72,7 @@ struct tegra_kbc {
 	unsigned int repoll_dly;
 	unsigned long cp_dly_jiffies;
 	bool use_fn_map;
+	bool use_ghost_filter;
 	const struct tegra_kbc_platform_data *pdata;
 	unsigned short keycode[KBC_MAX_KEY * 2];
 	unsigned short current_keys[KBC_MAX_KPENT];
@@ -260,6 +261,8 @@ static void tegra_kbc_report_keys(struct tegra_kbc *kbc)
 	unsigned int num_down = 0;
 	unsigned long flags;
 	bool fn_keypress = false;
+	bool key_in_same_row = false;
+	bool key_in_same_col = false;
 
 	spin_lock_irqsave(&kbc->lock, flags);
 	for (i = 0; i < KBC_MAX_KPENT; i++) {
@@ -284,6 +287,34 @@ static void tegra_kbc_report_keys(struct tegra_kbc *kbc)
 		val >>= 8;
 	}
 
+	/*
+	 * Matrix keyboard designs are prone to keyboard ghosting.
+	 * Ghosting occurs if there are 3 keys such that -
+	 * any 2 of the 3 keys share a row, and any 2 of them share a column.
+	 * If so ignore the key presses for this iteration.
+	 */
+	if ((kbc->use_ghost_filter) && (num_down >= 3)) {
+		for (i = 0; i < num_down; i++) {
+			unsigned int j;
+			u8 curr_col = scancodes[i] & 0x07;
+			u8 curr_row = scancodes[i] >> KBC_ROW_SHIFT;
+
+			/*
+			 * Find 2 keys such that one key is in the same row
+			 * and the other is in the same column as the i-th key.
+			 */
+			for (j = i + 1; j < num_down; j++) {
+				u8 col = scancodes[j] & 0x07;
+				u8 row = scancodes[j] >> KBC_ROW_SHIFT;
+
+				if (col == curr_col)
+					key_in_same_col = true;
+				if (row == curr_row)
+					key_in_same_row = true;
+			}
+		}
+	}
+
 	/*
 	 * If the platform uses Fn keymaps, translate keys on a Fn keypress.
 	 * Function keycodes are KBC_MAX_KEY apart from the plain keycodes.
@@ -297,6 +328,10 @@ static void tegra_kbc_report_keys(struct tegra_kbc *kbc)
 
 	spin_unlock_irqrestore(&kbc->lock, flags);
 
+	/* Ignore the key presses for this iteration? */
+	if (key_in_same_col && key_in_same_row)
+		return;
+
 	tegra_kbc_report_released_keys(kbc->idev,
 				       kbc->current_keys, kbc->num_pressed_keys,
 				       keycodes, num_down);
@@ -652,6 +687,7 @@ static int __devinit tegra_kbc_probe(struct platform_device *pdev)
 		input_dev->keycodemax *= 2;
 
 	kbc->use_fn_map = pdata->use_fn_map;
+	kbc->use_ghost_filter = pdata->use_ghost_filter;
 	keymap_data = pdata->keymap_data ?: &tegra_kbc_default_keymap_data;
 	matrix_keypad_build_keymap(keymap_data, KBC_ROW_SHIFT,
 				   input_dev->keycode, input_dev->keybit);