Investigate matrix_keypad linux driver

[amclain]

Linux has a built-in matrix_keypad driver that we may be able to use for scanning and programming the keyboard matrix.

Example device tree:

        matrix_keypad: matrix_keypad0 {
                compatible = "gpio-matrix-keypad";
                debounce-delay-ms = <5>;
                col-scan-delay-us = <2>;
                row-gpios = <&gpio1 25 GPIO_ACTIVE_HIGH         /* Bank1, pin25 */
                             &gpio1 26 GPIO_ACTIVE_HIGH         /* Bank1, pin26 */
                             &gpio1 27 GPIO_ACTIVE_HIGH>;       /* Bank1, pin27 */
                col-gpios = <&gpio1 21 GPIO_ACTIVE_HIGH         /* Bank1, pin21 */
                             &gpio1 22 GPIO_ACTIVE_HIGH>;       /* Bank1, pin22 */
                linux,keymap = <0x0000008b      /* MENU */
                                0x0100009e      /* BACK */
                                0x02000069      /* LEFT */
                                0x0001006a      /* RIGHT */
                                0x0101001c      /* ENTER */
                                0x0201006c>;    /* DOWN */
        };  

See dt-bindings/input/linux-event-codes.h.

[doughsay]

This is interesting, but I don't like how they turn it into keycodes; I'd rather get back the raw info of which key in the matrix was pressed and not have it impose opinions about which keys correspond to which keycodes. Is it also not possible to distinguish between key-up and key-down events? Also, this is still running in linux, and therefore susceptible to fair scheduling. We still like the PRU idea better because it's real-time, right?

[amclain]

I titled this issue as "investigate" because I don't know the answers to all of those questions yet. This came as a suggestion from Frank, so I wanted to capture it so we can evaluate it at some point.