HID: core: statically allocate read buffers

This is a preparation patch for rethinking the generic processing
of HID reports.

We can actually pre-allocate all of our memory instead of dynamically
allocating/freeing it whenever we parse a report.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: Ping Cheng <ping.cheng@wacom.com>
Acked-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Author: bentiss

drivers/hid/hid-core.c

@@ -101,14 +101,15 @@ static struct hid_field *hid_register_field(struct hid_report *report, unsigned
 
 	field = kzalloc((sizeof(struct hid_field) +
 			 usages * sizeof(struct hid_usage) +
-			 usages * sizeof(unsigned)), GFP_KERNEL);
+			 2 * usages * sizeof(unsigned int)), GFP_KERNEL);
 	if (!field)
 		return NULL;
 
 	field->index = report->maxfield++;
 	report->field[field->index] = field;
 	field->usage = (struct hid_usage *)(field + 1);
 	field->value = (s32 *)(field->usage + usages);
+	field->new_value = (s32 *)(field->value + usages);
 	field->report = report;
 
 	return field;
@@ -1541,9 +1542,8 @@ static void hid_input_field(struct hid_device *hid, struct hid_field *field,
 	__s32 max = field->logical_maximum;
 	__s32 *value;
 
-	value = kmalloc_array(count, sizeof(__s32), GFP_ATOMIC);
-	if (!value)
-		return;
+	value = field->new_value;
+	memset(value, 0, count * sizeof(__s32));
 
 	for (n = 0; n < count; n++) {
 
@@ -1557,7 +1557,7 @@ static void hid_input_field(struct hid_device *hid, struct hid_field *field,
 		    value[n] >= min && value[n] <= max &&
 		    value[n] - min < field->maxusage &&
 		    field->usage[value[n] - min].hid == HID_UP_KEYBOARD + 1)
-			goto exit;
+			return;
 	}
 
 	for (n = 0; n < count; n++) {
@@ -1581,8 +1581,6 @@ static void hid_input_field(struct hid_device *hid, struct hid_field *field,
 	}
 
 	memcpy(field->value, value, count * sizeof(__s32));
-exit:
-	kfree(value);
 }
 
 /*

include/linux/hid.h

@@ -476,6 +476,7 @@ struct hid_field {
 	unsigned  report_count;		/* number of this field in the report */
 	unsigned  report_type;		/* (input,output,feature) */
 	__s32    *value;		/* last known value(s) */
+	__s32    *new_value;		/* newly read value(s) */
 	__s32     logical_minimum;
 	__s32     logical_maximum;
 	__s32     physical_minimum;