uclogic: Support disabling pen usage

Restore the ability to disable pen usage in hid-uclogic to support e.g.
keyboard interfaces which also have pen usages for some reason, but
which we don't want to rewrite report descriptors for.

Author: spbnick

hid-uclogic-core.c

@@ -84,6 +84,24 @@ static __u8 *uclogic_report_fixup(struct hid_device *hdev, __u8 *rdesc,
 	return rdesc;
 }
 
+static int uclogic_input_mapping(struct hid_device *hdev,
+				 struct hid_input *hi,
+				 struct hid_field *field,
+				 struct hid_usage *usage,
+				 unsigned long **bit,
+				 int *max)
+{
+	struct uclogic_drvdata *drvdata = hid_get_drvdata(hdev);
+	struct uclogic_params *params = &drvdata->params;
+
+	/* Discard invalid pen usages */
+	if (params->pen.usage_invalid && (field->application == HID_DG_PEN))
+		return -1;
+
+	/* Let hid-core decide what to do */
+	return 0;
+}
+
 #if KERNEL_VERSION(4, 4, 0) > LINUX_VERSION_CODE
 #define RETURN_SUCCESS return
 static void uclogic_input_configured(struct hid_device *hdev,
@@ -525,6 +543,7 @@ static struct hid_driver uclogic_driver = {
 	.remove = uclogic_remove,
 	.report_fixup = uclogic_report_fixup,
 	.raw_event = uclogic_raw_event,
+	.input_mapping = uclogic_input_mapping,
 	.input_configured = uclogic_input_configured,
 #ifdef CONFIG_PM
 	.resume	          = uclogic_resume,

hid-uclogic-params.h

@@ -61,6 +61,11 @@ struct uclogic_params_pen_subreport {
  * Noop (preserving functionality) when filled with zeroes.
  */
 struct uclogic_params_pen {
+	/*
+	 * True if pen usage is invalid for this interface and should be
+	 * ignored, false otherwise.
+	 */
+	bool usage_invalid;
 	/*
 	 * Pointer to report descriptor part describing the pen inputs.
 	 * Allocated with kmalloc. NULL if the part is not specified.
@@ -214,6 +219,7 @@ extern int uclogic_params_init(struct uclogic_params *params,
 	".desc_ptr = %p\n"                  \
 	".desc_size = %u\n"                 \
 	".pen = {\n"                        \
+	"\t.usage_invalid = %s\n"           \
 	"\t.desc_ptr = %p\n"                \
 	"\t.desc_size = %u\n"               \
 	"\t.id = %u\n"                      \
@@ -270,6 +276,7 @@ extern int uclogic_params_init(struct uclogic_params *params,
 	((_params)->invalid ? "true" : "false"),                    \
 	(_params)->desc_ptr,                                        \
 	(_params)->desc_size,                                       \
+	((_params)->pen.usage_invalid ? "true" : "false"),          \
 	(_params)->pen.desc_ptr,                                    \
 	(_params)->pen.desc_size,                                   \
 	(_params)->pen.id,                                          \