[PATCH v2 1/4] drm/dp: Add wait_hpd_asserted() callback to struct drm_dp_aux

[Douglas Anderson]

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 at linaro.org>
Signed-off-by: Douglas Anderson <dianders at chromium.org>
---
Left Dmitry's Reviewed-by tag off since patch changed enough.

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

 include/drm/dp/drm_dp_helper.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/include/drm/dp/drm_dp_helper.h b/include/drm/dp/drm_dp_helper.h
index 53d1e722f4de..0940c415db8c 100644
--- a/include/drm/dp/drm_dp_helper.h
+++ b/include/drm/dp/drm_dp_helper.h
@@ -2035,6 +2035,32 @@ 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 up to `wait_us` microseconds
+	 * for HPD to be asserted and might sleep.
+	 *
+	 * 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. If you want to do a quick poll you could pass 1
+	 * for `wait_us`.
+	 *
+	 * 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.
 	 */
-- 
2.36.0.rc0.470.gd361397f0d-goog