linux-kernel - [PATCH v3 20/20] extcon: intel-cht-wc: Report RID

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Date:   Sun, 28 Nov 2021 19:18:09 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Mark Gross <markgross@...nel.org>,
        Andy Shevchenko <andy@...radead.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        Sebastian Reichel <sre@...nel.org>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Ard Biesheuvel <ardb@...nel.org>
Cc:     Hans de Goede <hdegoede@...hat.com>, Len Brown <lenb@...nel.org>,
        linux-acpi@...r.kernel.org, Yauhen Kharuzhy <jekhor@...il.com>,
        Tsuchiya Yuto <kitakar@...il.com>,
        platform-driver-x86@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org
Subject: [PATCH v3 20/20] extcon: intel-cht-wc: Report RID_A for ACA adapters

Make cht_wc_extcon_get_id() report RID_A for ACA adapters, instead of
reporting ID_FLOAT.

According to the spec. we should read the USB-ID pin ADC value
to determine the resistance of the used pull-down resister and
then return RID_A / RID_B / RID_C based on this. But all "Accessory
Charger Adapter"s (ACAs) which users can actually buy always use
a combination of a charging port with one or more USB-A ports, so
they should always use a resistor indicating RID_A. But the spec
is hard to read / badly-worded so some of them actually indicate
they are a RID_B ACA even though they clearly are a RID_A ACA.

To workaround this simply always return INTEL_USB_RID_A, which
matches all the ACAs which users can actually buy.

Signed-off-by: Hans de Goede <hdegoede@...hat.com>
---
 drivers/extcon/extcon-intel-cht-wc.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/extcon/extcon-intel-cht-wc.c b/drivers/extcon/extcon-intel-cht-wc.c
index 144cb5d8cd47..2a8d41cbf41c 100644
--- a/drivers/extcon/extcon-intel-cht-wc.c
+++ b/drivers/extcon/extcon-intel-cht-wc.c
@@ -121,13 +121,21 @@ static int cht_wc_extcon_get_id(struct cht_wc_extcon_data *ext, int pwrsrc_sts)
 		return INTEL_USB_ID_GND;
 	case CHT_WC_PWRSRC_RID_FLOAT:
 		return INTEL_USB_ID_FLOAT;
+	/*
+	 * According to the spec. we should read the USB-ID pin ADC value here
+	 * to determine the resistance of the used pull-down resister and then
+	 * return RID_A / RID_B / RID_C based on this. But all "Accessory
+	 * Charger Adapter"s (ACAs) which users can actually buy always use
+	 * a combination of a charging port with one or more USB-A ports, so
+	 * they should always use a resistor indicating RID_A. But the spec
+	 * is hard to read / badly-worded so some of them actually indicate
+	 * they are a RID_B ACA evnen though they clearly are a RID_A ACA.
+	 * To workaround this simply always return INTEL_USB_RID_A, which
+	 * matches all the ACAs which users can actually buy.
+	 */
 	case CHT_WC_PWRSRC_RID_ACA:
+		return INTEL_USB_RID_A;
 	default:
-		/*
-		 * Once we have IIO support for the GPADC we should read
-		 * the USBID GPADC channel here and determine ACA role
-		 * based on that.
-		 */
 		return INTEL_USB_ID_FLOAT;
 	}
 }
-- 
2.33.1