ASoC: wcd-mbhc: correct special headset detection logic

When detecting special headset, vref for special headset is
set based on headset threshold reference 1800mv or based on
regular micbias settings from device tree. Scale threshold
reference as per the special headset micbias voltage.

Change-Id: Ic4cc24e18efeb420b53a2154707c9399eb886181
Signed-off-by: Meng Wang <mwang@codeaurora.org>

asoc/codecs/wcd934x/wcd934x-mbhc.c

@@ -1,6 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0-only
 /*
- * Copyright (c) 2015-2018, The Linux Foundation. All rights reserved.
+ * Copyright (c) 2015-2019, The Linux Foundation. All rights reserved.
  */
 #include <linux/module.h>
 #include <linux/init.h>
@@ -1102,6 +1102,7 @@ int tavil_mbhc_init(struct wcd934x_mbhc **mbhc,
 	struct wcd934x_mbhc *wcd934x_mbhc;
 	struct wcd_mbhc *wcd_mbhc;
 	int ret;
+	struct wcd9xxx_pdata *pdata;
 
 	wcd934x_mbhc = devm_kzalloc(component->dev, sizeof(struct wcd934x_mbhc),
 				    GFP_KERNEL);
@@ -1122,6 +1123,14 @@ int tavil_mbhc_init(struct wcd934x_mbhc **mbhc,
 	/* Setting default mbhc detection logic to ADC for Tavil */
 	wcd_mbhc->mbhc_detection_logic = WCD_DETECTION_ADC;
 
+	pdata = dev_get_platdata(component->dev->parent);
+	if (!pdata) {
+		dev_err(component->dev, "%s: pdata pointer is NULL\n", __func__);
+		ret = -EINVAL;
+		goto err;
+	}
+	wcd_mbhc->micb_mv = pdata->micbias.micb2_mv;
+
 	ret = wcd_mbhc_init(wcd_mbhc, component, &mbhc_cb,
 				&intr_ids, wcd_mbhc_registers,
 				TAVIL_ZDET_SUPPORTED);