Commit 4261b2f9 authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Peter Maydell
Browse files

nrf51_gpio: reflect pull-up/pull-down to IRQs 



Some drivers do I2C bitbanging by keeping the output to 0 and flipping
the GPIO direction between input and output (see for example in Linux
gpio_set_open_drain_value_commit, in drivers/gpio/gpiolib.c).
When the GPIO is set to input, the pull-up resistor brings the output
to 1, while when the GPIO is set to output, the output driver brings
the output to 0.

Implement this for the nRF51 GPIO device model.  First, if both input and
output are floating, and there is a pull-up or pull-down resistor
configured, do not just set s->in, but also make any devices listening
on the output qemu_irq receive that value.  Second, if the pin is
driven both internally (output pin) and externally you don't get a
short circuit if both sides drive the pin to the same value.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Acked-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Message-id: 20190317141001.3346-1-pbonzini@redhat.com
[PMM: wrapped long line]
Reviewed-by: default avatarPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: default avatarPeter Maydell <peter.maydell@linaro.org>
parent a036f530

hw/gpio/nrf51_gpio.c

+40 −25
Original line number Diff line number Diff line
@@ -43,6 +43,17 @@ static bool is_connected(uint32_t config, uint32_t level) 
    return state;

}



static int pull_value(uint32_t config)

{

    int pull = extract32(config, 2, 2);

    if (pull == NRF51_GPIO_PULLDOWN) {

        return 0;

    } else if (pull == NRF51_GPIO_PULLUP) {

        return 1;

    }

    return -1;

}



static void update_output_irq(NRF51GPIOState *s, size_t i,

                              bool connected, bool level)

{
@@ -61,43 +72,47 @@ static void update_output_irq(NRF51GPIOState *s, size_t i, 


static void update_state(NRF51GPIOState *s)

{

    uint32_t pull;

    int pull;

    size_t i;

    bool connected_out, dir, connected_in, out, input;

    bool connected_out, dir, connected_in, out, in, input;



    for (i = 0; i < NRF51_GPIO_PINS; i++) {

        pull = extract32(s->cnf[i], 2, 2);

        pull = pull_value(s->cnf[i]);

        dir = extract32(s->cnf[i], 0, 1);

        connected_in = extract32(s->in_mask, i, 1);

        out = extract32(s->out, i, 1);

        in = extract32(s->in, i, 1);

        input = !extract32(s->cnf[i], 1, 1);

        connected_out = is_connected(s->cnf[i], out) && dir;



        update_output_irq(s, i, connected_out, out);



        if (!input) {

            if (pull >= 0) {

                /* Input buffer disconnected from external drives */

                s->in = deposit32(s->in, i, 1, pull);

            }

        } else {

            if (connected_out && connected_in && out != in) {

                /* Pin both driven externally and internally */

        if (connected_out && connected_in) {

            qemu_log_mask(LOG_GUEST_ERROR, "GPIO pin %zu short circuited\n", i);

                qemu_log_mask(LOG_GUEST_ERROR,

                              "GPIO pin %zu short circuited\n", i);

            }



            if (!connected_in) {

                /*

         * Input buffer disconnected from internal/external drives, so

         * pull-up/pull-down becomes relevant

                 * Floating input: the output stimulates IN if connected,

                 * otherwise pull-up/pull-down resistors put a value on both

                 * IN and OUT.

                 */

        if (!input || (input && !connected_in && !connected_out)) {

            if (pull == NRF51_GPIO_PULLDOWN) {

                s->in = deposit32(s->in, i, 1, 0);

            } else if (pull == NRF51_GPIO_PULLUP) {

                s->in = deposit32(s->in, i, 1, 1);

                if (pull >= 0 && !connected_out) {

                    connected_out = true;

                    out = pull;

                }

        }



        /* Self stimulation through internal output driver */

        if (connected_out && !connected_in && input) {

                if (connected_out) {

                    s->in = deposit32(s->in, i, 1, out);

                }

            }



        }

        update_output_irq(s, i, connected_out, out);

    }

}



/*