[PATCH v2 1/2] Input: mt6779-keypad - fix hardware code mapping

[Mattijs Korpershoek <mkorpershoek@baylibre.com>]

In mt6779_keypad_irq_handler(), we
1. Read a hardware code from KPD_MEM1 -> KPD_MEM5
2. Use that hardware code to compute columns/rows for the standard
   keyboard matrix.

According to the (non-public) datasheet, the
map between the hardware code and the cols/rows is:

        |(0)  |(1)  |(2)
    ----*-----*-----*-----
        |     |     |
        |(9)  |(10) |(11)
    ----*-----*-----*-----
        |     |     |
        |(18) |(19) |(20)
    ----*-----*-----*-----
        |     |     |

This brings us to another formula:
-> row = code / 9;
-> col = code % 3;

Implement this mapping in bitnr_to_col_row() to fetch the
correct input event from keypad->input_dev->keycode and report that
back to userspace.

Fixes: f28af984e771 ("Input: mt6779-keypad - add MediaTek keypad driver")
Co-developed-by: Fabien Parent <fparent@baylibre.com>
Signed-off-by: Fabien Parent <fparent@baylibre.com>
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
---
 drivers/input/keyboard/mt6779-keypad.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/input/keyboard/mt6779-keypad.c b/drivers/input/keyboard/mt6779-keypad.c
index 2e7c9187c10f..23360de20da5 100644
--- a/drivers/input/keyboard/mt6779-keypad.c
+++ b/drivers/input/keyboard/mt6779-keypad.c
@@ -36,6 +36,19 @@ static const struct regmap_config mt6779_keypad_regmap_cfg = {
 	.max_register = 36,
 };
 
+/*
+ * | hardware key code | col0 | col1 | col2|
+ * | ----------------- | -----| ---- | --- |
+ * | row0              | 0    | 1    | 2   |
+ * | row1              | 9    | 10   | 11  |
+ * | row2              | 18   | 19   | 20  |
+ */
+static void bitnr_to_col_row(int bit_nr, int *col, int *row)
+{
+	*row = bit_nr / 9;
+	*col = bit_nr % 3;
+}
+
 static irqreturn_t mt6779_keypad_irq_handler(int irq, void *dev_id)
 {
 	struct mt6779_keypad *keypad = dev_id;
@@ -61,8 +74,7 @@ static irqreturn_t mt6779_keypad_irq_handler(int irq, void *dev_id)
 		if (bit_nr % 32 >= 16)
 			continue;
 
-		row = bit_nr / 32;
-		col = bit_nr % 32;
+		bitnr_to_col_row(bit_nr, &col, &row);
 		scancode = MATRIX_SCAN_CODE(row, col, row_shift);
 		/* 1: not pressed, 0: pressed */
 		pressed = !test_bit(bit_nr, new_state);
-- 
2.34.1