[PATCH] Generic HID layer - code split (dde5845a) · Commits · e / devices / android_kernel_fairphone_FP5

drivers/hid/hid-core.c

0 → 100644

+940 −0

Original line number	Original line	Diff line number	Diff line
			/*
			* 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;
			}