HID: uclogic: Support in-range reporting emulation

Newer UC-Logic tablets, such as ones made by Huion have stopped
reporting in-range state, but they're otherwise worthy tablets. The
manufacturer was notified of the problem and promised to fix this in the
future. Meanwhile, detect pen coming in range, and emulate the reports
to the userspace, to make the tablets useable.
Signed-off-by: Nikolai Kondrashov <spbnick@gmail.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

drivers/hid/hid-uclogic-core.c

@@ -16,6 +16,7 @@
 #include <linux/device.h>
 #include <linux/hid.h>
 #include <linux/module.h>
+#include <linux/timer.h>
 #include "usbhid/usbhid.h"
 #include "hid-uclogic-params.h"
 
@@ -32,8 +33,40 @@ struct uclogic_drvdata {
 	 * Only valid if desc_ptr is not NULL
 	 */
 	unsigned int desc_size;
+	/* Pen input device */
+	struct input_dev *pen_input;
+	/* In-range timer */
+	struct timer_list inrange_timer;
 };
 
+/**
+ * uclogic_inrange_timeout - handle pen in-range state timeout.
+ * Emulate input events normally generated when pen goes out of range for
+ * tablets which don't report that.
+ *
+ * @t:	The timer the timeout handler is attached to, stored in a struct
+ *	uclogic_drvdata.
+ */
+static void uclogic_inrange_timeout(struct timer_list *t)
+{
+	struct uclogic_drvdata *drvdata = from_timer(drvdata, t,
+							inrange_timer);
+	struct input_dev *input = drvdata->pen_input;
+
+	if (input == NULL)
+		return;
+	input_report_abs(input, ABS_PRESSURE, 0);
+	/* If BTN_TOUCH state is changing */
+	if (test_bit(BTN_TOUCH, input->key)) {
+		input_event(input, EV_MSC, MSC_SCAN,
+				/* Digitizer Tip Switch usage */
+				0xd0042);
+		input_report_key(input, BTN_TOUCH, 0);
+	}
+	input_report_key(input, BTN_TOOL_PEN, 0);
+	input_sync(input);
+}
+
 static __u8 *uclogic_report_fixup(struct hid_device *hdev, __u8 *rdesc,
 					unsigned int *rsize)
 {
@@ -67,6 +100,8 @@ static int uclogic_input_mapping(struct hid_device *hdev,
 static int uclogic_input_configured(struct hid_device *hdev,
 		struct hid_input *hi)
 {
+	struct uclogic_drvdata *drvdata = hid_get_drvdata(hdev);
+	struct uclogic_params *params = &drvdata->params;
 	char *name;
 	const char *suffix = NULL;
 	struct hid_field *field;
@@ -76,6 +111,15 @@ static int uclogic_input_configured(struct hid_device *hdev,
 	if (!hi->report)
 		return 0;
 
+	/*
+	 * If this is the input corresponding to the pen report
+	 * in need of tweaking.
+	 */
+	if (hi->report->id == params->pen.id) {
+		/* Remember the input device so we can simulate events */
+		drvdata->pen_input = hi->input;
+	}
+
 	field = hi->report->field[0];
 
 	switch (field->application) {
@@ -130,6 +174,7 @@ static int uclogic_probe(struct hid_device *hdev,
 		rc = -ENOMEM;
 		goto failure;
 	}
+	timer_setup(&drvdata->inrange_timer, uclogic_inrange_timeout, 0);
 	hid_set_drvdata(hdev, drvdata);
 
 	/* Initialize the device and retrieve interface parameters */
@@ -220,6 +265,14 @@ static int uclogic_raw_event(struct hid_device *hdev,
 			/* Invert the in-range bit */
 			data[1] ^= 0x40;
 		}
+		/* If we need to emulate in-range detection */
+		if (params->pen.inrange == UCLOGIC_PARAMS_PEN_INRANGE_NONE) {
+			/* Set in-range bit */
+			data[1] |= 0x40;
+			/* (Re-)start in-range timeout */
+			mod_timer(&drvdata->inrange_timer,
+					jiffies + msecs_to_jiffies(100));
+		}
 	}
 
 	return 0;
@@ -229,6 +282,7 @@ static void uclogic_remove(struct hid_device *hdev)
 {
 	struct uclogic_drvdata *drvdata = hid_get_drvdata(hdev);
 
+	del_timer_sync(&drvdata->inrange_timer);
 	hid_hw_stop(hdev);
 	kfree(drvdata->desc_ptr);
 	uclogic_params_cleanup(&drvdata->params);

drivers/hid/hid-uclogic-params.c

@@ -36,6 +36,8 @@ const char *uclogic_params_pen_inrange_to_str(
 		return "normal";
 	case UCLOGIC_PARAMS_PEN_INRANGE_INVERTED:
 		return "inverted";
+	case UCLOGIC_PARAMS_PEN_INRANGE_NONE:
+		return "none";
 	default:
 		return NULL;
 	}

drivers/hid/hid-uclogic-params.h

@@ -25,6 +25,8 @@ enum uclogic_params_pen_inrange {
 	UCLOGIC_PARAMS_PEN_INRANGE_NORMAL = 0,
 	/* Inverted reports: zero - in proximity, one - out of proximity */
 	UCLOGIC_PARAMS_PEN_INRANGE_INVERTED,
+	/* No reports */
+	UCLOGIC_PARAMS_PEN_INRANGE_NONE,
 };
 
 /* Convert a pen in-range reporting type to a string */