Fix -EPIPE/-ENODATA errors after writing to sysfs entries in quick su…

…ccession (#83)

* Add a 200ms sleep after sending ctrl reports to some devices
* Add D5 Next into the mix & convert to switch case

Signed-off-by: Aleksa Savic <savicaleksa83@gmail.com>

aquacomputer_d5next.c

@@ -14,6 +14,7 @@
 
 #include <linux/crc16.h>
 #include <linux/debugfs.h>
+#include <linux/delay.h>
 #include <linux/hid.h>
 #include <linux/hwmon.h>
 #include <linux/hwmon-sysfs.h>
@@ -833,6 +834,31 @@ static int aqc_send_ctrl_data(struct aqc_data *priv)
 	    hid_hw_raw_request(priv->hdev, priv->secondary_ctrl_report_id,
 			       priv->secondary_ctrl_report, priv->secondary_ctrl_report_size,
 			       HID_FEATURE_REPORT, HID_REQ_SET_REPORT);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Wait 200ms before returning to make sure that the device actually processed both reports
+	 * and saved ctrl data to memory. Otherwise, an aqc_get_ctrl_data() call made shortly after
+	 * may fail with -EPIPE because the device is still busy and can't provide data. This can
+	 * happen when userspace tools, such as fancontrol or liquidctl, write to sysfs entries in
+	 * quick succession (for example, setting pwmX_enable and pwmX attributes at once).
+	 *
+	 * 200ms was found to be the sweet spot between fixing the issue and not significantly
+	 * prolonging the call. Quadro, Octo, D5 Next and Aquaero are currently known to be
+	 * affected.
+	 */
+	switch (priv->kind) {
+	case quadro:
+	case octo:
+	case d5next:
+	case aquaero:
+		msleep(200);
+		break;
+	default:
+		break;
+	}
+
 	return ret;
 }