drm/msm/dp: wait for hpd high before aux transaction

The source device should ensure the sink is ready before proceeding to
read the sink capability or perform any aux transactions. The sink
will indicate its readiness by asserting the HPD line. The controller
driver needs to wait for the hpd line to be asserted by the sink before
it performs any aux transactions.

The eDP sink is assumed to be always connected. It needs power from the
source and its HPD line will be asserted only after the panel is powered
on. The panel power will be enabled from the panel-edp driver and only
after that, the hpd line will be asserted.

Whereas for DP, the sink can be hotplugged and unplugged anytime. The hpd
line gets asserted to indicate the sink is connected and ready. Hence
there is no need to wait for the hpd line to be asserted for a DP sink.

Signed-off-by: Sankeerth Billakanti <quic_sbillaka@quicinc.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/483312/
Link: https://lore.kernel.org/r/1650887072-16652-4-git-send-email-quic_sbillaka@quicinc.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

1 files changed, 20 insertions, 1 deletions

diff --git a/drivers/gpu/drm/msm/dp/dp_aux.c b/drivers/gpu/drm/msm/dp/dp_aux.c
index 6d36f63c3338..d030a93a08c3 100644
--- a/drivers/gpu/drm/msm/dp/dp_aux.c
+++ b/drivers/gpu/drm/msm/dp/dp_aux.c
@@ -34,6 +34,7 @@ struct dp_aux_private {
 	bool no_send_addr;
 	bool no_send_stop;
 	bool initted;
+	bool is_edp;
 	u32 offset;
 	u32 segment;
 
@@ -337,6 +338,22 @@ static ssize_t dp_aux_transfer(struct drm_dp_aux *dp_aux,
 		goto exit;
 	}
 
+	/*
+	 * For eDP it's important to give a reasonably long wait here for HPD
+	 * to be asserted. This is because the panel driver may have _just_
+	 * turned on the panel and then tried to do an AUX transfer. The panel
+	 * driver has no way of knowing when the panel is ready, so it's up
+	 * to us to wait. For DP we never get into this situation so let's
+	 * avoid ever doing the extra long wait for DP.
+	 */
+	if (aux->is_edp) {
+		ret = dp_catalog_aux_wait_for_hpd_connect_state(aux->catalog);
+		if (ret) {
+			DRM_DEBUG_DP("Panel not ready for aux transactions\n");
+			goto exit;
+		}
+	}
+
 	dp_aux_update_offset_and_segment(aux, msg);
 	dp_aux_transfer_helper(aux, msg, true);
 
@@ -491,7 +508,8 @@ void dp_aux_unregister(struct drm_dp_aux *dp_aux)
 	drm_dp_aux_unregister(dp_aux);
 }
 
-struct drm_dp_aux *dp_aux_get(struct device *dev, struct dp_catalog *catalog)
+struct drm_dp_aux *dp_aux_get(struct device *dev, struct dp_catalog *catalog,
+			      bool is_edp)
 {
 	struct dp_aux_private *aux;
 
@@ -506,6 +524,7 @@ struct drm_dp_aux *dp_aux_get(struct device *dev, struct dp_catalog *catalog)
 
 	init_completion(&aux->comp);
 	aux->cmd_busy = false;
+	aux->is_edp = is_edp;
 	mutex_init(&aux->mutex);
 
 	aux->dev = dev;