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 <[e-mail]>
Reviewed-by: Douglas Anderson <[e-mail]>
Reviewed-by: Stephen Boyd <[e-mail]>
Patchwork: https://patchwork.freedesktop.org/patch/483312/
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dmitry Baryshkov <[e-mail]>

drivers/gpu/drm/msm/dp/dp_aux.c

···
 	bool no_send_addr;
 	bool no_send_stop;
 	bool initted;
+	bool is_edp;
 	u32 offset;
 	u32 segment;
 
···
 		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);
 
···
 	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;
 
···
 
 	init_completion(&aux->comp);
 	aux->cmd_busy = false;
+	aux->is_edp = is_edp;
 	mutex_init(&aux->mutex);
 
 	aux->dev = dev;

drivers/gpu/drm/msm/dp/dp_aux.h

···
 void dp_aux_deinit(struct drm_dp_aux *dp_aux);
 void dp_aux_reconfig(struct drm_dp_aux *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);
 void dp_aux_put(struct drm_dp_aux *aux);
 
 #endif /*__DP_AUX_H_*/

drivers/gpu/drm/msm/dp/dp_catalog.c

···
 	phy_calibrate(phy);
 }
 
+int dp_catalog_aux_wait_for_hpd_connect_state(struct dp_catalog *dp_catalog)
+{
+	u32 state;
+	struct dp_catalog_private *catalog = container_of(dp_catalog,
+				struct dp_catalog_private, dp_catalog);
+
+	/* poll for hpd connected status every 2ms and timeout after 500ms */
+	return readl_poll_timeout(catalog->io->dp_controller.aux.base +
+				REG_DP_DP_HPD_INT_STATUS,
+				state, state & DP_DP_HPD_STATE_STATUS_CONNECTED,
+				2000, 500000);
+}
+
 static void dump_regs(void __iomem *base, int len)
 {
 	int i;

drivers/gpu/drm/msm/dp/dp_catalog.h

···
 void dp_catalog_aux_reset(struct dp_catalog *dp_catalog);
 void dp_catalog_aux_enable(struct dp_catalog *dp_catalog, bool enable);
 void dp_catalog_aux_update_cfg(struct dp_catalog *dp_catalog);
+int dp_catalog_aux_wait_for_hpd_connect_state(struct dp_catalog *dp_catalog);
 u32 dp_catalog_aux_get_irq(struct dp_catalog *dp_catalog);
 
 /* DP Controller APIs */

drivers/gpu/drm/msm/dp/dp_display.c

···
 		goto error;
 	}
 
-	dp->aux = dp_aux_get(dev, dp->catalog);
+	dp->aux = dp_aux_get(dev, dp->catalog, dp->dp_display.is_edp);
 	if (IS_ERR(dp->aux)) {
 		rc = PTR_ERR(dp->aux);
 		DRM_ERROR("failed to initialize aux, rc = %d\n", rc);