drivers/hid/hid-core.c

/*
 *  USB HID support for Linux
 *
 *  Copyright (c) 1999 Andreas Gal
 *  Copyright (c) 2000-2005 Vojtech Pavlik <vojtech@suse.cz>
 *  Copyright (c) 2005 Michael Haboustak <mike-@cinci.rr.com> for Concept2, Inc
 *  Copyright (c) 2006 Jiri Kosina
 */

/*
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 */

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <linux/smp_lock.h>
#include <linux/spinlock.h>
#include <asm/unaligned.h>
#include <asm/byteorder.h>
#include <linux/input.h>
#include <linux/wait.h>

#undef DEBUG
#undef DEBUG_DATA

#include <linux/usb.h>

#include <linux/hid.h>
#include <linux/hiddev.h>

/*
 * Version Information
 */

#define DRIVER_VERSION "v2.6"
#define DRIVER_AUTHOR "Andreas Gal, Vojtech Pavlik"
#define DRIVER_DESC "USB HID core driver"
#define DRIVER_LICENSE "GPL"

/*
 * Module parameters.
 */

static unsigned int hid_mousepoll_interval;
module_param_named(mousepoll, hid_mousepoll_interval, uint, 0644);
MODULE_PARM_DESC(mousepoll, "Polling interval of mice");

/*
 * Register a new report for a device.
 */

static struct hid_report *hid_register_report(struct hid_device *device, unsigned type, unsigned id)
{
	struct hid_report_enum *report_enum = device->report_enum + type;
	struct hid_report *report;

	if (report_enum->report_id_hash[id])
		return report_enum->report_id_hash[id];

	if (!(report = kzalloc(sizeof(struct hid_report), GFP_KERNEL)))
		return NULL;

	if (id != 0)
		report_enum->numbered = 1;

	report->id = id;
	report->type = type;
	report->size = 0;
	report->device = device;
	report_enum->report_id_hash[id] = report;

	list_add_tail(&report->list, &report_enum->report_list);

	return report;
}

/*
 * Register a new field for this report.
 */

static struct hid_field *hid_register_field(struct hid_report *report, unsigned usages, unsigned values)
{
	struct hid_field *field;

	if (report->maxfield == HID_MAX_FIELDS) {
		dbg("too many fields in report");
		return NULL;
	}

	if (!(field = kzalloc(sizeof(struct hid_field) + usages * sizeof(struct hid_usage)
		+ values * sizeof(unsigned), GFP_KERNEL))) return NULL;

	field->index = report->maxfield++;
	report->field[field->index] = field;
	field->usage = (struct hid_usage *)(field + 1);
	field->value = (unsigned *)(field->usage + usages);
	field->report = report;

	return field;
}

/*
 * Open a collection. The type/usage is pushed on the stack.
 */

static int open_collection(struct hid_parser *parser, unsigned type)
{
	struct hid_collection *collection;
	unsigned usage;

	usage = parser->local.usage[0];

	if (parser->collection_stack_ptr == HID_COLLECTION_STACK_SIZE) {
		dbg("collection stack overflow");
		return -1;
	}

	if (parser->device->maxcollection == parser->device->collection_size) {
		collection = kmalloc(sizeof(struct hid_collection) *
				parser->device->collection_size * 2, GFP_KERNEL);
		if (collection == NULL) {
			dbg("failed to reallocate collection array");
			return -1;
		}
		memcpy(collection, parser->device->collection,
			sizeof(struct hid_collection) *
			parser->device->collection_size);
		memset(collection + parser->device->collection_size, 0,
			sizeof(struct hid_collection) *
			parser->device->collection_size);
		kfree(parser->device->collection);
		parser->device->collection = collection;
		parser->device->collection_size *= 2;
	}

	parser->collection_stack[parser->collection_stack_ptr++] =
		parser->device->maxcollection;

	collection = parser->device->collection +
		parser->device->maxcollection++;
	collection->type = type;
	collection->usage = usage;
	collection->level = parser->collection_stack_ptr - 1;

	if (type == HID_COLLECTION_APPLICATION)
		parser->device->maxapplication++;

	return 0;
}

/*
 * Close a collection.
 */

static int close_collection(struct hid_parser *parser)
{
	if (!parser->collection_stack_ptr) {
		dbg("collection stack underflow");
		return -1;
	}
	parser->collection_stack_ptr--;
	return 0;
}

/*
 * Climb up the stack, search for the specified collection type
 * and return the usage.
 */

static unsigned hid_lookup_collection(struct hid_parser *parser, unsigned type)
{
	int n;
	for (n = parser->collection_stack_ptr - 1; n >= 0; n--)
		if (parser->device->collection[parser->collection_stack[n]].type == type)
			return parser->device->collection[parser->collection_stack[n]].usage;
	return 0; /* we know nothing about this usage type */
}

/*
 * Add a usage to the temporary parser table.
 */

static int hid_add_usage(struct hid_parser *parser, unsigned usage)
{
	if (parser->local.usage_index >= HID_MAX_USAGES) {
		dbg("usage index exceeded");
		return -1;
	}
	parser->local.usage[parser->local.usage_index] = usage;
	parser->local.collection_index[parser->local.usage_index] =
		parser->collection_stack_ptr ?
		parser->collection_stack[parser->collection_stack_ptr - 1] : 0;
	parser->local.usage_index++;
	return 0;
}

/*
 * Register a new field for this report.
 */

static int hid_add_field(struct hid_parser *parser, unsigned report_type, unsigned flags)
{
	struct hid_report *report;
	struct hid_field *field;
	int usages;
	unsigned offset;
	int i;

	if (!(report = hid_register_report(parser->device, report_type, parser->global.report_id))) {
		dbg("hid_register_report failed");
		return -1;
	}

	if (parser->global.logical_maximum < parser->global.logical_minimum) {
		dbg("logical range invalid %d %d", parser->global.logical_minimum, parser->global.logical_maximum);
		return -1;
	}

	offset = report->size;
	report->size += parser->global.report_size * parser->global.report_count;

	if (!parser->local.usage_index) /* Ignore padding fields */
		return 0;

	usages = max_t(int, parser->local.usage_index, parser->global.report_count);

	if ((field = hid_register_field(report, usages, parser->global.report_count)) == NULL)
		return 0;

	field->physical = hid_lookup_collection(parser, HID_COLLECTION_PHYSICAL);
	field->logical = hid_lookup_collection(parser, HID_COLLECTION_LOGICAL);
	field->application = hid_lookup_collection(parser, HID_COLLECTION_APPLICATION);

	for (i = 0; i < usages; i++) {
		int j = i;
		/* Duplicate the last usage we parsed if we have excess values */
		if (i >= parser->local.usage_index)
			j = parser->local.usage_index - 1;
		field->usage[i].hid = parser->local.usage[j];
		field->usage[i].collection_index =
			parser->local.collection_index[j];
	}

	field->maxusage = usages;
	field->flags = flags;
	field->report_offset = offset;
	field->report_type = report_type;
	field->report_size = parser->global.report_size;
	field->report_count = parser->global.report_count;
	field->logical_minimum = parser->global.logical_minimum;
	field->logical_maximum = parser->global.logical_maximum;
	field->physical_minimum = parser->global.physical_minimum;
	field->physical_maximum = parser->global.physical_maximum;
	field->unit_exponent = parser->global.unit_exponent;
	field->unit = parser->global.unit;

	return 0;
}

/*
 * Read data value from item.
 */

static u32 item_udata(struct hid_item *item)
{
	switch (item->size) {
		case 1: return item->data.u8;
		case 2: return item->data.u16;
		case 4: return item->data.u32;
	}
	return 0;
}

static s32 item_sdata(struct hid_item *item)
{
	switch (item->size) {
		case 1: return item->data.s8;
		case 2: return item->data.s16;
		case 4: return item->data.s32;
	}
	return 0;
}

/*
 * Process a global item.
 */

static int hid_parser_global(struct hid_parser *parser, struct hid_item *item)
{
	switch (item->tag) {

		case HID_GLOBAL_ITEM_TAG_PUSH:

			if (parser->global_stack_ptr == HID_GLOBAL_STACK_SIZE) {
				dbg("global enviroment stack overflow");
				return -1;
			}

			memcpy(parser->global_stack + parser->global_stack_ptr++,
				&parser->global, sizeof(struct hid_global));
			return 0;

		case HID_GLOBAL_ITEM_TAG_POP:

			if (!parser->global_stack_ptr) {
				dbg("global enviroment stack underflow");
				return -1;
			}

			memcpy(&parser->global, parser->global_stack + --parser->global_stack_ptr,
				sizeof(struct hid_global));
			return 0;

		case HID_GLOBAL_ITEM_TAG_USAGE_PAGE:
			parser->global.usage_page = item_udata(item);
			return 0;

		case HID_GLOBAL_ITEM_TAG_LOGICAL_MINIMUM:
			parser->global.logical_minimum = item_sdata(item);
			return 0;

		case HID_GLOBAL_ITEM_TAG_LOGICAL_MAXIMUM:
			if (parser->global.logical_minimum < 0)
				parser->global.logical_maximum = item_sdata(item);
			else
				parser->global.logical_maximum = item_udata(item);
			return 0;

		case HID_GLOBAL_ITEM_TAG_PHYSICAL_MINIMUM:
			parser->global.physical_minimum = item_sdata(item);
			return 0;

		case HID_GLOBAL_ITEM_TAG_PHYSICAL_MAXIMUM:
			if (parser->global.physical_minimum < 0)
				parser->global.physical_maximum = item_sdata(item);
			else
				parser->global.physical_maximum = item_udata(item);
			return 0;

		case HID_GLOBAL_ITEM_TAG_UNIT_EXPONENT:
			parser->global.unit_exponent = item_sdata(item);
			return 0;

		case HID_GLOBAL_ITEM_TAG_UNIT:
			parser->global.unit = item_udata(item);
			return 0;

		case HID_GLOBAL_ITEM_TAG_REPORT_SIZE:
			if ((parser->global.report_size = item_udata(item)) > 32) {
				dbg("invalid report_size %d", parser->global.report_size);
				return -1;
			}
			return 0;

		case HID_GLOBAL_ITEM_TAG_REPORT_COUNT:
			if ((parser->global.report_count = item_udata(item)) > HID_MAX_USAGES) {
				dbg("invalid report_count %d", parser->global.report_count);
				return -1;
			}
			return 0;

		case HID_GLOBAL_ITEM_TAG_REPORT_ID:
			if ((parser->global.report_id = item_udata(item)) == 0) {
				dbg("report_id 0 is invalid");
				return -1;
			}
			return 0;

		default:
			dbg("unknown global tag 0x%x", item->tag);
			return -1;
	}
}

/*
 * Process a local item.
 */

static int hid_parser_local(struct hid_parser *parser, struct hid_item *item)
{
	__u32 data;
	unsigned n;

	if (item->size == 0) {
		dbg("item data expected for local item");
		return -1;
	}

	data = item_udata(item);

	switch (item->tag) {

		case HID_LOCAL_ITEM_TAG_DELIMITER:

			if (data) {
				/*
				 * We treat items before the first delimiter
				 * as global to all usage sets (branch 0).
				 * In the moment we process only these global
				 * items and the first delimiter set.
				 */
				if (parser->local.delimiter_depth != 0) {
					dbg("nested delimiters");
					return -1;
				}
				parser->local.delimiter_depth++;
				parser->local.delimiter_branch++;
			} else {
				if (parser->local.delimiter_depth < 1) {
					dbg("bogus close delimiter");
					return -1;
				}
				parser->local.delimiter_depth--;
			}
			return 1;

		case HID_LOCAL_ITEM_TAG_USAGE:

			if (parser->local.delimiter_branch > 1) {
				dbg("alternative usage ignored");
				return 0;
			}

			if (item->size <= 2)
				data = (parser->global.usage_page << 16) + data;

			return hid_add_usage(parser, data);

		case HID_LOCAL_ITEM_TAG_USAGE_MINIMUM:

			if (parser->local.delimiter_branch > 1) {
				dbg("alternative usage ignored");
				return 0;
			}

			if (item->size <= 2)
				data = (parser->global.usage_page << 16) + data;

			parser->local.usage_minimum = data;
			return 0;

		case HID_LOCAL_ITEM_TAG_USAGE_MAXIMUM:

			if (parser->local.delimiter_branch > 1) {
				dbg("alternative usage ignored");
				return 0;
			}

			if (item->size <= 2)
				data = (parser->global.usage_page << 16) + data;

			for (n = parser->local.usage_minimum; n <= data; n++)
				if (hid_add_usage(parser, n)) {
					dbg("hid_add_usage failed\n");
					return -1;
				}
			return 0;

		default:

			dbg("unknown local item tag 0x%x", item->tag);
			return 0;
	}
	return 0;
}

/*
 * Process a main item.
 */

static int hid_parser_main(struct hid_parser *parser, struct hid_item *item)
{
	__u32 data;
	int ret;

	data = item_udata(item);

	switch (item->tag) {
		case HID_MAIN_ITEM_TAG_BEGIN_COLLECTION:
			ret = open_collection(parser, data & 0xff);
			break;
		case HID_MAIN_ITEM_TAG_END_COLLECTION:
			ret = close_collection(parser);
			break;
		case HID_MAIN_ITEM_TAG_INPUT:
			ret = hid_add_field(parser, HID_INPUT_REPORT, data);
			break;
		case HID_MAIN_ITEM_TAG_OUTPUT:
			ret = hid_add_field(parser, HID_OUTPUT_REPORT, data);
			break;
		case HID_MAIN_ITEM_TAG_FEATURE:
			ret = hid_add_field(parser, HID_FEATURE_REPORT, data);
			break;
		default:
			dbg("unknown main item tag 0x%x", item->tag);
			ret = 0;
	}

	memset(&parser->local, 0, sizeof(parser->local));	/* Reset the local parser environment */

	return ret;
}

/*
 * Process a reserved item.
 */

static int hid_parser_reserved(struct hid_parser *parser, struct hid_item *item)
{
	dbg("reserved item type, tag 0x%x", item->tag);
	return 0;
}

/*
 * Free a report and all registered fields. The field->usage and
 * field->value table's are allocated behind the field, so we need
 * only to free(field) itself.
 */

static void hid_free_report(struct hid_report *report)
{
	unsigned n;

	for (n = 0; n < report->maxfield; n++)
		kfree(report->field[n]);
	kfree(report);
}

/*
 * Free a device structure, all reports, and all fields.
 */

static void hid_free_device(struct hid_device *device)
{
	unsigned i,j;

	for (i = 0; i < HID_REPORT_TYPES; i++) {
		struct hid_report_enum *report_enum = device->report_enum + i;

		for (j = 0; j < 256; j++) {
			struct hid_report *report = report_enum->report_id_hash[j];
			if (report)
				hid_free_report(report);
		}
	}

	kfree(device->rdesc);
	kfree(device);
}

/*
 * Fetch a report description item from the data stream. We support long
 * items, though they are not used yet.
 */

static u8 *fetch_item(__u8 *start, __u8 *end, struct hid_item *item)
{
	u8 b;

	if ((end - start) <= 0)
		return NULL;

	b = *start++;

	item->type = (b >> 2) & 3;
	item->tag  = (b >> 4) & 15;

	if (item->tag == HID_ITEM_TAG_LONG) {

		item->format = HID_ITEM_FORMAT_LONG;

		if ((end - start) < 2)
			return NULL;

		item->size = *start++;
		item->tag  = *start++;

		if ((end - start) < item->size)
			return NULL;

		item->data.longdata = start;
		start += item->size;
		return start;
	}

	item->format = HID_ITEM_FORMAT_SHORT;
	item->size = b & 3;

	switch (item->size) {

		case 0:
			return start;

		case 1:
			if ((end - start) < 1)
				return NULL;
			item->data.u8 = *start++;
			return start;

		case 2:
			if ((end - start) < 2)
				return NULL;
			item->data.u16 = le16_to_cpu(get_unaligned((__le16*)start));
			start = (__u8 *)((__le16 *)start + 1);
			return start;

		case 3:
			item->size++;
			if ((end - start) < 4)
				return NULL;
			item->data.u32 = le32_to_cpu(get_unaligned((__le32*)start));
			start = (__u8 *)((__le32 *)start + 1);
			return start;
	}

	return NULL;
}

/*
 * Parse a report description into a hid_device structure. Reports are
 * enumerated, fields are attached to these reports.
 */

static struct hid_device *hid_parse_report(__u8 *start, unsigned size)
{
	struct hid_device *device;
	struct hid_parser *parser;
	struct hid_item item;
	__u8 *end;
	unsigned i;
	static int (*dispatch_type[])(struct hid_parser *parser,
				      struct hid_item *item) = {
		hid_parser_main,
		hid_parser_global,
		hid_parser_local,
		hid_parser_reserved
	};

	if (!(device = kzalloc(sizeof(struct hid_device), GFP_KERNEL)))
		return NULL;

	if (!(device->collection = kzalloc(sizeof(struct hid_collection) *
				   HID_DEFAULT_NUM_COLLECTIONS, GFP_KERNEL))) {
		kfree(device);
		return NULL;
	}
	device->collection_size = HID_DEFAULT_NUM_COLLECTIONS;

	for (i = 0; i < HID_REPORT_TYPES; i++)
		INIT_LIST_HEAD(&device->report_enum[i].report_list);

	if (!(device->rdesc = (__u8 *)kmalloc(size, GFP_KERNEL))) {
		kfree(device->collection);
		kfree(device);
		return NULL;
	}
	memcpy(device->rdesc, start, size);
	device->rsize = size;

	if (!(parser = kzalloc(sizeof(struct hid_parser), GFP_KERNEL))) {
		kfree(device->rdesc);
		kfree(device->collection);
		kfree(device);
		return NULL;
	}
	parser->device = device;

	end = start + size;
	while ((start = fetch_item(start, end, &item)) != NULL) {

		if (item.format != HID_ITEM_FORMAT_SHORT) {
			dbg("unexpected long global item");
			kfree(device->collection);
			hid_free_device(device);
			kfree(parser);
			return NULL;
		}

		if (dispatch_type[item.type](parser, &item)) {
			dbg("item %u %u %u %u parsing failed\n",
				item.format, (unsigned)item.size, (unsigned)item.type, (unsigned)item.tag);
			kfree(device->collection);
			hid_free_device(device);
			kfree(parser);
			return NULL;
		}

		if (start == end) {
			if (parser->collection_stack_ptr) {
				dbg("unbalanced collection at end of report description");
				kfree(device->collection);
				hid_free_device(device);
				kfree(parser);
				return NULL;
			}
			if (parser->local.delimiter_depth) {
				dbg("unbalanced delimiter at end of report description");
				kfree(device->collection);
				hid_free_device(device);
				kfree(parser);
				return NULL;
			}
			kfree(parser);
			return device;
		}
	}

	dbg("item fetching failed at offset %d\n", (int)(end - start));
	kfree(device->collection);
	hid_free_device(device);
	kfree(parser);
	return NULL;
}

/*
 * Convert a signed n-bit integer to signed 32-bit integer. Common
 * cases are done through the compiler, the screwed things has to be
 * done by hand.
 */

static s32 snto32(__u32 value, unsigned n)
{
	switch (n) {
		case 8:  return ((__s8)value);
		case 16: return ((__s16)value);
		case 32: return ((__s32)value);
	}
	return value & (1 << (n - 1)) ? value | (-1 << n) : value;
}

/*
 * Convert a signed 32-bit integer to a signed n-bit integer.
 */

static u32 s32ton(__s32 value, unsigned n)
{
	s32 a = value >> (n - 1);
	if (a && a != -1)
		return value < 0 ? 1 << (n - 1) : (1 << (n - 1)) - 1;
	return value & ((1 << n) - 1);
}

/*
 * Extract/implement a data field from/to a little endian report (bit array).
 *
 * Code sort-of follows HID spec:
 *     http://www.usb.org/developers/devclass_docs/HID1_11.pdf
 *
 * While the USB HID spec allows unlimited length bit fields in "report
 * descriptors", most devices never use more than 16 bits.
 * One model of UPS is claimed to report "LINEV" as a 32-bit field.
 * Search linux-kernel and linux-usb-devel archives for "hid-core extract".
 */

static __inline__ __u32 extract(__u8 *report, unsigned offset, unsigned n)
{
	u64 x;

	WARN_ON(n > 32);

	report += offset >> 3;  /* adjust byte index */
	offset &= 7;		/* now only need bit offset into one byte */
	x = get_unaligned((u64 *) report);
	x = le64_to_cpu(x);
	x = (x >> offset) & ((1ULL << n) - 1);	/* extract bit field */
	return (u32) x;
}

/*
 * "implement" : set bits in a little endian bit stream.
 * Same concepts as "extract" (see comments above).
 * The data mangled in the bit stream remains in little endian
 * order the whole time. It make more sense to talk about
 * endianness of register values by considering a register
 * a "cached" copy of the little endiad bit stream.
 */
static __inline__ void implement(__u8 *report, unsigned offset, unsigned n, __u32 value)
{
	u64 x;
	u64 m = (1ULL << n) - 1;

	WARN_ON(n > 32);

	WARN_ON(value > m);
	value &= m;

	report += offset >> 3;
	offset &= 7;

	x = get_unaligned((u64 *)report);
	x &= cpu_to_le64(~(m << offset));
	x |= cpu_to_le64(((u64) value) << offset);
	put_unaligned(x, (u64 *) report);
}

/*
 * Search an array for a value.
 */

static __inline__ int search(__s32 *array, __s32 value, unsigned n)
{
	while (n--) {
		if (*array++ == value)
			return 0;
	}
	return -1;
}

static void hid_process_event(struct hid_device *hid, struct hid_field *field, struct hid_usage *usage, __s32 value, int interrupt)
{
	hid_dump_input(usage, value);
	if (hid->claimed & HID_CLAIMED_INPUT)
		hidinput_hid_event(hid, field, usage, value);
	if (hid->claimed & HID_CLAIMED_HIDDEV && interrupt)
		hiddev_hid_event(hid, field, usage, value);
}

/*
 * Analyse a received field, and fetch the data from it. The field
 * content is stored for next report processing (we do differential
 * reporting to the layer).
 */

static void hid_input_field(struct hid_device *hid, struct hid_field *field, __u8 *data, int interrupt)
{
	unsigned n;
	unsigned count = field->report_count;
	unsigned offset = field->report_offset;
	unsigned size = field->report_size;
	__s32 min = field->logical_minimum;
	__s32 max = field->logical_maximum;
	__s32 *value;

	if (!(value = kmalloc(sizeof(__s32) * count, GFP_ATOMIC)))
		return;

	for (n = 0; n < count; n++) {

			value[n] = min < 0 ? snto32(extract(data, offset + n * size, size), size) :
						    extract(data, offset + n * size, size);

			if (!(field->flags & HID_MAIN_ITEM_VARIABLE) /* Ignore report if ErrorRollOver */
			    && value[n] >= min && value[n] <= max
			    && field->usage[value[n] - min].hid == HID_UP_KEYBOARD + 1)
				goto exit;
	}

	for (n = 0; n < count; n++) {

		if (HID_MAIN_ITEM_VARIABLE & field->flags) {
			hid_process_event(hid, field, &field->usage[n], value[n], interrupt);
			continue;
		}

		if (field->value[n] >= min && field->value[n] <= max
			&& field->usage[field->value[n] - min].hid
			&& search(value, field->value[n], count))
				hid_process_event(hid, field, &field->usage[field->value[n] - min], 0, interrupt);

		if (value[n] >= min && value[n] <= max
			&& field->usage[value[n] - min].hid
			&& search(field->value, value[n], count))
				hid_process_event(hid, field, &field->usage[value[n] - min], 1, interrupt);
	}

	memcpy(field->value, value, count * sizeof(__s32));
exit:
	kfree(value);
}


/*
 * Output the field into the report.
 */

static void hid_output_field(struct hid_field *field, __u8 *data)
{
	unsigned count = field->report_count;
	unsigned offset = field->report_offset;
	unsigned size = field->report_size;
	unsigned n;

	for (n = 0; n < count; n++) {
		if (field->logical_minimum < 0)	/* signed values */
			implement(data, offset + n * size, size, s32ton(field->value[n], size));
		else				/* unsigned values */
			implement(data, offset + n * size, size, field->value[n]);
	}
}

/*
 * Create a report.
 */

static void hid_output_report(struct hid_report *report, __u8 *data)
{
	unsigned n;

	if (report->id > 0)
		*data++ = report->id;

	for (n = 0; n < report->maxfield; n++)
		hid_output_field(report->field[n], data);
}

/*
 * Set a field value. The report this field belongs to has to be
 * created and transferred to the device, to set this value in the
 * device.
 */

int hid_set_field(struct hid_field *field, unsigned offset, __s32 value)
{
	unsigned size = field->report_size;

	hid_dump_input(field->usage + offset, value);

	if (offset >= field->report_count) {
		dbg("offset (%d) exceeds report_count (%d)", offset, field->report_count);
		hid_dump_field(field, 8);
		return -1;
	}
	if (field->logical_minimum < 0) {
		if (value != snto32(s32ton(value, size), size)) {
			dbg("value %d is out of range", value);
			return -1;
		}
	}
	field->value[offset] = value;
	return 0;
}