diff options
Diffstat (limited to 'include/drm/display/drm_dp_helper.h')
| -rw-r--r-- | include/drm/display/drm_dp_helper.h | 48 |
1 files changed, 45 insertions, 3 deletions
diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h index dca40a045dd6..db0fe9f8a612 100644 --- a/include/drm/display/drm_dp_helper.h +++ b/include/drm/display/drm_dp_helper.h @@ -370,14 +370,56 @@ struct drm_dp_aux { * helpers assume this is the case. * * Also note that this callback can be called no matter the - * state @dev is in. Drivers that need that device to be powered - * to perform this operation will first need to make sure it's - * been properly enabled. + * state @dev is in and also no matter what state the panel is + * in. It's expected: + * + * - If the @dev providing the AUX bus is currently unpowered then + * it will power itself up for the transfer. + * + * - If we're on eDP (using a drm_panel) and the panel is not in a + * state where it can respond (it's not powered or it's in a + * low power state) then this function may return an error, but + * not crash. It's up to the caller of this code to make sure that + * the panel is powered on if getting an error back is not OK. If a + * drm_panel driver is initiating a DP AUX transfer it may power + * itself up however it wants. All other code should ensure that + * the pre_enable() bridge chain (which eventually calls the + * drm_panel prepare function) has powered the panel. */ 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. */ unsigned i2c_nack_count; |