drm/nouveau/dp: Honor GSP link training retry timeouts

Turns out that one of the ways that Nvidia's driver handles the pre-LT
timeout for eDP panels is by providing a retry timeout in their link
training callbacks that we're expected to wait for. Up until now we didn't
pay any attention to this parameter.

So, start honoring the timeout if link training fails - and retry up to 3
times. The "3 times" bit comes from OpenRM's link training code.

[airlied: this fixes the panel on one of my laptops]
Signed-off-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231222043308.3090089-12-airlied@gmail.com

drivers/gpu/drm/nouveau/nvkm/engine/disp/r535.c

@@ -957,40 +957,60 @@ r535_dp_train_target(struct nvkm_outp *outp, u8 target, bool mst, u8 link_nr, u8
 {
 	struct nvkm_disp *disp = outp->disp;
 	NV0073_CTRL_DP_CTRL_PARAMS *ctrl;
-	int ret;
-
-	ctrl = nvkm_gsp_rm_ctrl_get(&disp->rm.objcom, NV0073_CTRL_CMD_DP_CTRL, sizeof(*ctrl));
-	if (IS_ERR(ctrl))
-		return PTR_ERR(ctrl);
+	int ret, retries;
+	u32 cmd, data;
 
-	ctrl->subDeviceInstance = 0;
-	ctrl->displayId = BIT(outp->index);
-	ctrl->cmd = NVDEF(NV0073_CTRL, DP_CMD, SET_LANE_COUNT, TRUE) |
-		    NVDEF(NV0073_CTRL, DP_CMD, SET_LINK_BW, TRUE) |
-		    NVDEF(NV0073_CTRL, DP_CMD, TRAIN_PHY_REPEATER, YES);
-	ctrl->data = NVVAL(NV0073_CTRL, DP_DATA, SET_LANE_COUNT, link_nr) |
-		     NVVAL(NV0073_CTRL, DP_DATA, SET_LINK_BW, link_bw) |
-		     NVVAL(NV0073_CTRL, DP_DATA, TARGET, target);
+	cmd = NVDEF(NV0073_CTRL, DP_CMD, SET_LANE_COUNT, TRUE) |
+	      NVDEF(NV0073_CTRL, DP_CMD, SET_LINK_BW, TRUE) |
+	      NVDEF(NV0073_CTRL, DP_CMD, TRAIN_PHY_REPEATER, YES);
+	data = NVVAL(NV0073_CTRL, DP_DATA, SET_LANE_COUNT, link_nr) |
+	       NVVAL(NV0073_CTRL, DP_DATA, SET_LINK_BW, link_bw) |
+	       NVVAL(NV0073_CTRL, DP_DATA, TARGET, target);
 
 	if (mst)
-		ctrl->cmd |= NVDEF(NV0073_CTRL, DP_CMD, SET_FORMAT_MODE, MULTI_STREAM);
+		cmd |= NVDEF(NV0073_CTRL, DP_CMD, SET_FORMAT_MODE, MULTI_STREAM);
 
 	if (outp->dp.dpcd[DPCD_RC02] & DPCD_RC02_ENHANCED_FRAME_CAP)
-		ctrl->cmd |= NVDEF(NV0073_CTRL, DP_CMD, SET_ENHANCED_FRAMING, TRUE);
+		cmd |= NVDEF(NV0073_CTRL, DP_CMD, SET_ENHANCED_FRAMING, TRUE);
 
 	if (target == 0 &&
 	     (outp->dp.dpcd[DPCD_RC02] & 0x20) &&
 	    !(outp->dp.dpcd[DPCD_RC03] & DPCD_RC03_TPS4_SUPPORTED))
-	    ctrl->cmd |= NVDEF(NV0073_CTRL, DP_CMD, POST_LT_ADJ_REQ_GRANTED, YES);
+		cmd |= NVDEF(NV0073_CTRL, DP_CMD, POST_LT_ADJ_REQ_GRANTED, YES);
 
-	ret = nvkm_gsp_rm_ctrl_push(&disp->rm.objcom, &ctrl, sizeof(*ctrl));
-	if (ret) {
-		nvkm_gsp_rm_ctrl_done(&disp->rm.objcom, ctrl);
-		return ret;
+	/* We should retry up to 3 times, but only if GSP asks politely */
+	for (retries = 0; retries < 3; ++retries) {
+		ctrl = nvkm_gsp_rm_ctrl_get(&disp->rm.objcom, NV0073_CTRL_CMD_DP_CTRL,
+					    sizeof(*ctrl));
+		if (IS_ERR(ctrl))
+			return PTR_ERR(ctrl);
+
+		ctrl->subDeviceInstance = 0;
+		ctrl->displayId = BIT(outp->index);
+		ctrl->retryTimeMs = 0;
+		ctrl->cmd = cmd;
+		ctrl->data = data;
+
+		ret = nvkm_gsp_rm_ctrl_push(&disp->rm.objcom, &ctrl, sizeof(*ctrl));
+		if (ret == -EAGAIN && ctrl->retryTimeMs) {
+			/*
+			 * Device (likely an eDP panel) isn't ready yet, wait for the time specified
+			 * by GSP before retrying again
+			 */
+			nvkm_debug(&disp->engine.subdev,
+				   "Waiting %dms for GSP LT panel delay before retrying\n",
+				   ctrl->retryTimeMs);
+			msleep(ctrl->retryTimeMs);
+			nvkm_gsp_rm_ctrl_done(&disp->rm.objcom, ctrl);
+		} else {
+			/* GSP didn't say to retry, or we were successful */
+			if (ctrl->err)
+				ret = -EIO;
+			nvkm_gsp_rm_ctrl_done(&disp->rm.objcom, ctrl);
+			break;
+		}
 	}
 
-	ret = ctrl->err ? -EIO : 0;
-	nvkm_gsp_rm_ctrl_done(&disp->rm.objcom, ctrl);
 	return ret;
 }