platform/chrome: wilco_ec: Add Dell's USB PowerShare Policy control

USB PowerShare is a policy which affects charging via the special
USB PowerShare port (marked with a small lightning bolt or battery icon)
when in low power states:
- In S0, the port will always provide power.
- In S0ix, if usb_charge is enabled, then power will be supplied to
  the port when on AC or if battery is > 50%. Else no power is supplied.
- In S5, if usb_charge is enabled, then power will be supplied to
  the port when on AC. Else no power is supplied.
Signed-off-by: Daniel Campello <campello@chromium.org>
Signed-off-by: Nick Crews <ncrews@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

Documentation/ABI/testing/sysfs-platform-wilco-ec

@@ -31,6 +31,23 @@ Description:
                Output will a version string be similar to the example below:
                08B6
 
+What:          /sys/bus/platform/devices/GOOG000C\:00/usb_charge
+Date:          October 2019
+KernelVersion: 5.5
+Description:
+               Control the USB PowerShare Policy. USB PowerShare is a policy
+               which affects charging via the special USB PowerShare port
+               (marked with a small lightning bolt or battery icon) when in
+               low power states:
+               - In S0, the port will always provide power.
+               - In S0ix, if usb_charge is enabled, then power will be
+                 supplied to the port when on AC or if battery is > 50%.
+                 Else no power is supplied.
+               - In S5, if usb_charge is enabled, then power will be supplied
+                 to the port when on AC. Else no power is supplied.
+
+               Input should be either "0" or "1".
+
 What:          /sys/bus/platform/devices/GOOG000C\:00/version
 Date:          May 2019
 KernelVersion: 5.3

drivers/platform/chrome/wilco_ec/sysfs.c

@@ -23,6 +23,26 @@ struct boot_on_ac_request {
 	u8 reserved7;
 } __packed;
 
+#define CMD_USB_CHARGE 0x39
+
+enum usb_charge_op {
+	USB_CHARGE_GET = 0,
+	USB_CHARGE_SET = 1,
+};
+
+struct usb_charge_request {
+	u8 cmd;		/* Always CMD_USB_CHARGE */
+	u8 reserved;
+	u8 op;		/* One of enum usb_charge_op */
+	u8 val;		/* When setting, either 0 or 1 */
+} __packed;
+
+struct usb_charge_response {
+	u8 reserved;
+	u8 status;	/* Set by EC to 0 on success, other value on failure */
+	u8 val;		/* When getting, set by EC to either 0 or 1 */
+} __packed;
+
 #define CMD_EC_INFO			0x38
 enum get_ec_info_op {
 	CMD_GET_EC_LABEL	= 0,
@@ -131,12 +151,83 @@ static ssize_t model_number_show(struct device *dev,
 
 static DEVICE_ATTR_RO(model_number);
 
+static int send_usb_charge(struct wilco_ec_device *ec,
+				struct usb_charge_request *rq,
+				struct usb_charge_response *rs)
+{
+	struct wilco_ec_message msg;
+	int ret;
+
+	memset(&msg, 0, sizeof(msg));
+	msg.type = WILCO_EC_MSG_LEGACY;
+	msg.request_data = rq;
+	msg.request_size = sizeof(*rq);
+	msg.response_data = rs;
+	msg.response_size = sizeof(*rs);
+	ret = wilco_ec_mailbox(ec, &msg);
+	if (ret < 0)
+		return ret;
+	if (rs->status)
+		return -EIO;
+
+	return 0;
+}
+
+static ssize_t usb_charge_show(struct device *dev,
+				    struct device_attribute *attr, char *buf)
+{
+	struct wilco_ec_device *ec = dev_get_drvdata(dev);
+	struct usb_charge_request rq;
+	struct usb_charge_response rs;
+	int ret;
+
+	memset(&rq, 0, sizeof(rq));
+	rq.cmd = CMD_USB_CHARGE;
+	rq.op = USB_CHARGE_GET;
+
+	ret = send_usb_charge(ec, &rq, &rs);
+	if (ret < 0)
+		return ret;
+
+	return sprintf(buf, "%d\n", rs.val);
+}
+
+static ssize_t usb_charge_store(struct device *dev,
+				     struct device_attribute *attr,
+				     const char *buf, size_t count)
+{
+	struct wilco_ec_device *ec = dev_get_drvdata(dev);
+	struct usb_charge_request rq;
+	struct usb_charge_response rs;
+	int ret;
+	u8 val;
+
+	ret = kstrtou8(buf, 10, &val);
+	if (ret < 0)
+		return ret;
+	if (val > 1)
+		return -EINVAL;
+
+	memset(&rq, 0, sizeof(rq));
+	rq.cmd = CMD_USB_CHARGE;
+	rq.op = USB_CHARGE_SET;
+	rq.val = val;
+
+	ret = send_usb_charge(ec, &rq, &rs);
+	if (ret < 0)
+		return ret;
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(usb_charge);
 
 static struct attribute *wilco_dev_attrs[] = {
 	&dev_attr_boot_on_ac.attr,
 	&dev_attr_build_date.attr,
 	&dev_attr_build_revision.attr,
 	&dev_attr_model_number.attr,
+	&dev_attr_usb_charge.attr,
 	&dev_attr_version.attr,
 	NULL,
 };