thermal: ti-soc-thermal: freeze FSM while computing trend

In order to read the history buffer, it is required to
freeze BG FSM. This patch adds the missing piece of code
to freeze the FSM and also a contention area to avoid
other parts of the code to access the DTEMPs.

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>

drivers/thermal/ti-soc-thermal/ti-bandgap.c

@@ -992,9 +992,12 @@ int ti_bandgap_get_trend(struct ti_bandgap *bgp, int id, int *trend)
 		goto exit;
 	}
 
+	spin_lock(&bgp->lock);
+
 	tsr = bgp->conf->sensors[id].registers;
 
 	/* Freeze and read the last 2 valid readings */
+	RMW_BITS(bgp, id, bgap_mask_ctrl, mask_freeze_mask, 1);
 	reg1 = tsr->ctrl_dtemp_1;
 	reg2 = tsr->ctrl_dtemp_2;
 
@@ -1008,22 +1011,25 @@ int ti_bandgap_get_trend(struct ti_bandgap *bgp, int id, int *trend)
 	/* Convert from adc values to mCelsius temperature */
 	ret = ti_bandgap_adc_to_mcelsius(bgp, temp1, &t1);
 	if (ret)
-		goto exit;
+		goto unfreeze;
 
 	ret = ti_bandgap_adc_to_mcelsius(bgp, temp2, &t2);
 	if (ret)
-		goto exit;
+		goto unfreeze;
 
 	/* Fetch the update interval */
 	ret = ti_bandgap_read_update_interval(bgp, id, &interval);
 	if (ret || !interval)
-		goto exit;
+		goto unfreeze;
 
 	*trend = (t1 - t2) / interval;
 
 	dev_dbg(bgp->dev, "The temperatures are t1 = %d and t2 = %d and trend =%d\n",
 		t1, t2, *trend);
 
+unfreeze:
+	RMW_BITS(bgp, id, bgap_mask_ctrl, mask_freeze_mask, 0);
+	spin_unlock(&bgp->lock);
 exit:
 	return ret;
 }