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    Subject[PATCH v4 1/4] drm/dp: Add wait_hpd_asserted() callback to struct drm_dp_aux
    Date
    Sometimes it's useful for users of the DP AUX bus (like panels) to be
    able to poll HPD. Let's add a callback that allows DP AUX busses
    drivers to provide this.

    Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
    Signed-off-by: Douglas Anderson <dianders@chromium.org>
    Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
    ---

    Changes in v4:
    - Comments now explain that we may wait longer due to debouncing.
    - Rebased to handle the fact that the stuct moved files.

    Changes in v2:
    - Change is_hpd_asserted() to wait_hpd_asserted()

    include/drm/display/drm_dp_helper.h | 30 +++++++++++++++++++++++++++++
    1 file changed, 30 insertions(+)

    diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h
    index c5f8f45511ed..db0fe9f8a612 100644
    --- a/include/drm/display/drm_dp_helper.h
    +++ b/include/drm/display/drm_dp_helper.h
    @@ -389,6 +389,36 @@ struct drm_dp_aux {
    ssize_t (*transfer)(struct drm_dp_aux *aux,
    struct drm_dp_aux_msg *msg);

    + /**
    + * @wait_hpd_asserted: wait for HPD to be asserted
    + *
    + * This is mainly useful for eDP panels drivers to wait for an eDP
    + * panel to finish powering on. This is an optional function.
    + *
    + * This function will efficiently wait for the HPD signal to be
    + * asserted. The `wait_us` parameter that is passed in says that we
    + * know that the HPD signal is expected to be asserted within `wait_us`
    + * microseconds. This function could wait for longer than `wait_us` if
    + * the logic in the DP controller has a long debouncing time. The
    + * important thing is that if this function returns success that the
    + * DP controller is ready to send AUX transactions.
    + *
    + * This function returns 0 if HPD was asserted or -ETIMEDOUT if time
    + * expired and HPD wasn't asserted. This function should not print
    + * timeout errors to the log.
    + *
    + * The semantics of this function are designed to match the
    + * readx_poll_timeout() function. That means a `wait_us` of 0 means
    + * to wait forever. Like readx_poll_timeout(), this function may sleep.
    + *
    + * NOTE: this function specifically reports the state of the HPD pin
    + * that's associated with the DP AUX channel. This is different from
    + * the HPD concept in much of the rest of DRM which is more about
    + * physical presence of a display. For eDP, for instance, a display is
    + * assumed always present even if the HPD pin is deasserted.
    + */
    + int (*wait_hpd_asserted)(struct drm_dp_aux *aux, unsigned long wait_us);
    +
    /**
    * @i2c_nack_count: Counts I2C NACKs, used for DP validation.
    */
    --
    2.36.1.476.g0c4daa206d-goog
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