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>

1 files changed, 36 insertions, 0 deletions

diff --git a/drivers/input/keyboard/tegra-kbc.c b/drivers/input/keyboard/tegra-kbc.c
index 99ce9032d08c..5fb4b972f205 100644
--- a/drivers/input/keyboard/tegra-kbc.c
+++ b/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++) {
@@ -285,6 +288,34 @@ static void tegra_kbc_report_keys(struct tegra_kbc *kbc)
         }
 
         /*
+         * 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);