source: mainline/uspace/lib/usb/src/request.c@ 97ab321

/*
 * Copyright (c) 2011 Vojtech Horky
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup libusb
 * @{
 */
/** @file
 * Standard USB requests (implementation).
 */
#include <usb/request.h>
#include <errno.h>
#include <assert.h>
#include <usb/debug.h>

#define MAX_DATA_LENGTH ((size_t)(0xFFFF))

/** Generic wrapper for SET requests using standard control request format.
 *
 * @see usb_pipe_control_write
 *
 * @param pipe Pipe used for the communication.
 * @param request_type Request type (standard/class/vendor).
 * @param recipient Request recipient (e.g. device or endpoint).
 * @param request Actual request (e.g. GET_DESCRIPTOR).
 * @param value Value of @c wValue field of setup packet
 *      (must be in USB endianness).
 * @param index Value of @c wIndex field of setup packet
 *      (must be in USB endianness).
 * @param data Data to be sent during DATA stage
 *      (expected to be in USB endianness).
 * @param data_size Size of the @p data buffer (in native endianness).
 * @return Error code.
 * @retval EBADMEM @p pipe is NULL.
 * @retval EBADMEM @p data is NULL and @p data_size is not zero.
 * @retval ERANGE Data buffer too large.
 */
int usb_control_request_set(usb_pipe_t *pipe,
    usb_request_type_t request_type, usb_request_recipient_t recipient,
    uint8_t request,
    uint16_t value, uint16_t index,
    void *data, size_t data_size)
{
        if (pipe == NULL) {
                return EBADMEM;
        }

        if (data_size > MAX_DATA_LENGTH) {
                return ERANGE;
        }

        if ((data_size > 0) && (data == NULL)) {
                return EBADMEM;
        }

        /*
         * TODO: check that @p request_type and @p recipient are
         * within ranges.
         */

        usb_device_request_setup_packet_t setup_packet;
        setup_packet.request_type = (request_type << 5) | recipient;
        setup_packet.request = request;
        setup_packet.value = value;
        setup_packet.index = index;
        setup_packet.length = (uint16_t) data_size;

        int rc = usb_pipe_control_write(pipe,
            &setup_packet, sizeof(setup_packet),
            data, data_size);

        return rc;
}

 /** Generic wrapper for GET requests using standard control request format.
  *
  * @see usb_pipe_control_read
  *
  * @param pipe Pipe used for the communication.
  * @param request_type Request type (standard/class/vendor).
  * @param recipient Request recipient (e.g. device or endpoint).
  * @param request Actual request (e.g. GET_DESCRIPTOR).
  * @param value Value of @c wValue field of setup packet
  *     (must be in USB endianness).
  * @param index Value of @c wIndex field of setup packet
  *     (must be in USB endianness).
  * @param data Buffer where to store data accepted during the DATA stage.
  *     (they will come in USB endianness).
  * @param data_size Size of the @p data buffer
  *     (in native endianness).
  * @param actual_data_size Actual size of transfered data
  *     (in native endianness).
  * @return Error code.
  * @retval EBADMEM @p pipe is NULL.
  * @retval EBADMEM @p data is NULL and @p data_size is not zero.
  * @retval ERANGE Data buffer too large.
  */
int usb_control_request_get(usb_pipe_t *pipe,
    usb_request_type_t request_type, usb_request_recipient_t recipient,
    uint8_t request,
    uint16_t value, uint16_t index,
    void *data, size_t data_size, size_t *actual_data_size)
{
        if (pipe == NULL) {
                return EBADMEM;
        }

        if (data_size > MAX_DATA_LENGTH) {
                return ERANGE;
        }

        if ((data_size > 0) && (data == NULL)) {
                return EBADMEM;
        }

        /*
         * TODO: check that @p request_type and @p recipient are
         * within ranges.
         */

        usb_device_request_setup_packet_t setup_packet;
        setup_packet.request_type = 128 | (request_type << 5) | recipient;
        setup_packet.request = request;
        setup_packet.value = value;
        setup_packet.index = index;
        setup_packet.length = (uint16_t) data_size;

        int rc = usb_pipe_control_read(pipe,
            &setup_packet, sizeof(setup_packet),
            data, data_size, actual_data_size);

        return rc;
}

/** Retrieve status of a USB device.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[in] index Recipient index (in native endianness).
 * @param[in] recipient Recipient of the GET_STATUS request.
 * @param[out] status Recipient status (in native endianness).
 * @return Error code.
 */
int usb_request_get_status(usb_pipe_t *pipe,
    usb_request_recipient_t recipient, uint16_t index,
    uint16_t *status)
{
        if ((recipient == USB_REQUEST_RECIPIENT_DEVICE) && (index != 0)) {
                return EINVAL;
        }

        if (status == NULL) {
                return EBADMEM;
        }

        uint16_t status_usb_endianess;
        size_t data_transfered_size;
        int rc = usb_control_request_get(pipe, USB_REQUEST_TYPE_STANDARD,
            recipient, USB_DEVREQ_GET_STATUS, 0, uint16_host2usb(index),
            &status_usb_endianess, 2, &data_transfered_size);
        if (rc != EOK) {
                return rc;
        }
        if (data_transfered_size != 2) {
                return ELIMIT;
        }

        *status = uint16_usb2host(status_usb_endianess);

        return EOK;
}

/** Clear or disable specific device feature.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[in] request_type Request type (standard/class/vendor).
 * @param[in] recipient Recipient of the CLEAR_FEATURE request.
 * @param[in] feature_selector Feature selector (in native endianness).
 * @param[in] index Recipient index (in native endianness).
 * @return Error code.
 */
int usb_request_clear_feature(usb_pipe_t *pipe,
    usb_request_type_t request_type, usb_request_recipient_t recipient,
    uint16_t feature_selector, uint16_t index)
{
        if (request_type == USB_REQUEST_TYPE_STANDARD) {
                if ((recipient == USB_REQUEST_RECIPIENT_DEVICE)
                    && (index != 0)) {
                        return EINVAL;
                }
        }

        int rc = usb_control_request_set(pipe, request_type, recipient,
            USB_DEVREQ_CLEAR_FEATURE,
            uint16_host2usb(feature_selector), uint16_host2usb(index),
            NULL, 0);

        return rc;
}

/** Set or enable specific device feature.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[in] request_type Request type (standard/class/vendor).
 * @param[in] recipient Recipient of the SET_FEATURE request.
 * @param[in] feature_selector Feature selector (in native endianness).
 * @param[in] index Recipient index (in native endianness).
 * @return Error code.
 */
int usb_request_set_feature(usb_pipe_t *pipe,
    usb_request_type_t request_type, usb_request_recipient_t recipient,
    uint16_t feature_selector, uint16_t index)
{
        if (request_type == USB_REQUEST_TYPE_STANDARD) {
                if ((recipient == USB_REQUEST_RECIPIENT_DEVICE)
                    && (index != 0)) {
                        return EINVAL;
                }
        }

        int rc = usb_control_request_set(pipe, request_type, recipient,
            USB_DEVREQ_SET_FEATURE,
            uint16_host2usb(feature_selector), uint16_host2usb(index),
            NULL, 0);

        return rc;
}

/** Change address of connected device.
 * This function automatically updates the backing connection to point to
 * the new address.
 *
 * @param pipe Control endpoint pipe (session must be already started).
 * @param new_address New USB address to be set (in native endianness).
 * @return Error code.
 */
int usb_request_set_address(usb_pipe_t *pipe,
    usb_address_t new_address)
{
        if ((new_address < 0) || (new_address >= USB11_ADDRESS_MAX)) {
                return EINVAL;
        }

        uint16_t addr = uint16_host2usb((uint16_t)new_address);

        int rc = usb_control_request_set(pipe,
            USB_REQUEST_TYPE_STANDARD, USB_REQUEST_RECIPIENT_DEVICE,
            USB_DEVREQ_SET_ADDRESS,
            addr, 0,
            NULL, 0);

        if (rc != EOK) {
                return rc;
        }

        assert(pipe->wire != NULL);
        /* TODO: prevent other from accessing wire now. */
        pipe->wire->address = new_address;

        return EOK;
}

/** Retrieve USB descriptor of a USB device.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[in] request_type Request type (standard/class/vendor).
 * @param[in] recipient Request recipient (device/interface/endpoint).
 * @param[in] descriptor_type Descriptor type (device/configuration/HID/...).
 * @param[in] descriptor_index Descriptor index.
 * @param[in] language Language index.
 * @param[out] buffer Buffer where to store the retrieved descriptor.
 * @param[in] size Size of the @p buffer.
 * @param[out] actual_size Number of bytes actually transferred.
 * @return Error code.
 */
int usb_request_get_descriptor(usb_pipe_t *pipe,
    usb_request_type_t request_type, usb_request_recipient_t recipient,
    uint8_t descriptor_type, uint8_t descriptor_index,
    uint16_t language,
    void *buffer, size_t size, size_t *actual_size)
{
        if (buffer == NULL) {
                return EBADMEM;
        }
        if (size == 0) {
                return EINVAL;
        }

        uint16_t wValue = descriptor_index | (descriptor_type << 8);

        return usb_control_request_get(pipe,
            request_type, recipient,
            USB_DEVREQ_GET_DESCRIPTOR,
            wValue, language,
            buffer, size, actual_size);
}

/** Retrieve USB descriptor, allocate space for it.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[in] request_type Request type (standard/class/vendor).
 * @param[in] recipient Request recipient (device/interface/endpoint).
 * @param[in] descriptor_type Descriptor type (device/configuration/HID/...).
 * @param[in] descriptor_index Descriptor index.
 * @param[in] language Language index.
 * @param[out] buffer_ptr Where to store pointer to allocated buffer.
 * @param[out] buffer_size Where to store the size of the descriptor.
 * @return
 */
int usb_request_get_descriptor_alloc(usb_pipe_t * pipe,
    usb_request_type_t request_type, usb_request_recipient_t recipient,
    uint8_t descriptor_type, uint8_t descriptor_index,
    uint16_t language,
    void **buffer_ptr, size_t *buffer_size)
{
        if (buffer_ptr == NULL) {
                return EBADMEM;
        }

        int rc;

        /*
         * Get only first byte to retrieve descriptor length.
         */
        uint8_t tmp_buffer[1];
        size_t bytes_transfered;
        rc = usb_request_get_descriptor(pipe, request_type, recipient,
            descriptor_type, descriptor_index, language,
            &tmp_buffer, 1, &bytes_transfered);
        if (rc != EOK) {
                return rc;
        }
        if (bytes_transfered != 1) {
                /* FIXME: some better error code? */
                return ESTALL;
        }

        size_t size = tmp_buffer[0];
        if (size == 0) {
                /* FIXME: some better error code? */
                return ESTALL;
        }

        /*
         * Allocate buffer and get the descriptor again.
         */
        void *buffer = malloc(size);
        if (buffer == NULL) {
                return ENOMEM;
        }

        rc = usb_request_get_descriptor(pipe, request_type, recipient,
            descriptor_type, descriptor_index, language,
            buffer, size, &bytes_transfered);
        if (rc != EOK) {
                free(buffer);
                return rc;
        }
        if (bytes_transfered != size) {
                free(buffer);
                /* FIXME: some better error code? */
                return ESTALL;
        }

        *buffer_ptr = buffer;
        if (buffer_size != NULL) {
                *buffer_size = size;
        }

        return EOK;
}

/** Retrieve standard device descriptor of a USB device.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[out] descriptor Storage for the device descriptor.
 * @return Error code.
 */
int usb_request_get_device_descriptor(usb_pipe_t *pipe,
    usb_standard_device_descriptor_t *descriptor)
{
        if (descriptor == NULL) {
                return EBADMEM;
        }

        size_t actually_transferred = 0;
        usb_standard_device_descriptor_t descriptor_tmp;
        int rc = usb_request_get_descriptor(pipe,
            USB_REQUEST_TYPE_STANDARD, USB_REQUEST_RECIPIENT_DEVICE, 
            USB_DESCTYPE_DEVICE, 0, 0,
            &descriptor_tmp, sizeof(descriptor_tmp),
            &actually_transferred);

        if (rc != EOK) {
                return rc;
        }

        /* Verify that all data has been transferred. */
        if (actually_transferred < sizeof(descriptor_tmp)) {
                return ELIMIT;
        }

        /* Everything is okay, copy the descriptor. */
        memcpy(descriptor, &descriptor_tmp,
            sizeof(descriptor_tmp));

        return EOK;
}

/** Retrieve configuration descriptor of a USB device.
 *
 * The function does not retrieve additional data binded with configuration
 * descriptor (such as its interface and endpoint descriptors) - use
 * usb_request_get_full_configuration_descriptor() instead.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[in] index Descriptor index.
 * @param[out] descriptor Storage for the device descriptor.
 * @return Error code.
 */
int usb_request_get_bare_configuration_descriptor(usb_pipe_t *pipe,
    int index, usb_standard_configuration_descriptor_t *descriptor)
{
        if (descriptor == NULL) {
                return EBADMEM;
        }

        if ((index < 0) || (index > 0xFF)) {
                return ERANGE;
        }

        size_t actually_transferred = 0;
        usb_standard_configuration_descriptor_t descriptor_tmp;
        int rc = usb_request_get_descriptor(pipe,
            USB_REQUEST_TYPE_STANDARD, USB_REQUEST_RECIPIENT_DEVICE,
            USB_DESCTYPE_CONFIGURATION, index, 0,
            &descriptor_tmp, sizeof(descriptor_tmp),
            &actually_transferred);
        if (rc != EOK) {
                return rc;
        }

        /* Verify that all data has been transferred. */
        if (actually_transferred < sizeof(descriptor_tmp)) {
                return ELIMIT;
        }

        /* Everything is okay, copy the descriptor. */
        memcpy(descriptor, &descriptor_tmp,
            sizeof(descriptor_tmp));

        return EOK;
}

/** Retrieve full configuration descriptor of a USB device.
 *
 * @warning The @p buffer might be touched (i.e. its contents changed)
 * even when error occurs.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[in] index Descriptor index.
 * @param[out] descriptor Storage for the device descriptor.
 * @param[in] descriptor_size Size of @p descriptor buffer.
 * @param[out] actual_size Number of bytes actually transferred.
 * @return Error code.
 */
int usb_request_get_full_configuration_descriptor(usb_pipe_t *pipe,
    int index, void *descriptor, size_t descriptor_size, size_t *actual_size)
{
        if ((index < 0) || (index > 0xFF)) {
                return ERANGE;
        }

        return usb_request_get_descriptor(pipe,
            USB_REQUEST_TYPE_STANDARD, USB_REQUEST_RECIPIENT_DEVICE,
            USB_DESCTYPE_CONFIGURATION, index, 0,
            descriptor, descriptor_size, actual_size);
}

/** Retrieve full configuration descriptor, allocate space for it.
 *
 * The function takes care that full configuration descriptor is returned
 * (i.e. the function will fail when less data then descriptor.totalLength
 * is returned).
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[in] index Configuration index.
 * @param[out] descriptor_ptr Where to store pointer to allocated buffer.
 * @param[out] descriptor_size Where to store the size of the descriptor.
 * @return Error code.
 */
int usb_request_get_full_configuration_descriptor_alloc(
    usb_pipe_t *pipe, int index,
    void **descriptor_ptr, size_t *descriptor_size)
{
        int rc;

        if (descriptor_ptr == NULL) {
                return EBADMEM;
        }

        usb_standard_configuration_descriptor_t bare_config;
        rc = usb_request_get_bare_configuration_descriptor(pipe, index,
            &bare_config);
        if (rc != EOK) {
                return rc;
        }
        if (bare_config.descriptor_type != USB_DESCTYPE_CONFIGURATION) {
                return ENOENT;
        }
        if (bare_config.total_length < sizeof(bare_config)) {
                return ELIMIT;
        }

        void *buffer = malloc(bare_config.total_length);
        if (buffer == NULL) {
                return ENOMEM;
        }

        size_t transferred = 0;
        rc = usb_request_get_full_configuration_descriptor(pipe, index,
            buffer, bare_config.total_length, &transferred);
        if (rc != EOK) {
                free(buffer);
                return rc;
        }

        if (transferred != bare_config.total_length) {
                free(buffer);
                return ELIMIT;
        }

        /* Everything looks okay, copy the pointers. */

        *descriptor_ptr = buffer;

        if (descriptor_size != NULL) {
                *descriptor_size = bare_config.total_length;
        }

        return EOK;
}

/** Update existing or add new USB descriptor to a USB device.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[in] request_type Request type (standard/class/vendor).
 * @param[in] recipient Request recipient (device/interface/endpoint).
 * @param[in] descriptor_type Descriptor type (device/configuration/HID/...).
 * @param[in] descriptor_index Descriptor index.
 * @param[in] language Language index (in native endianness).
 * @param[in] buffer Buffer with the new descriptor (in USB endianness).
 * @param[in] size Size of the @p buffer in bytes (in native endianness).
 * @return Error code.
 */
int usb_request_set_descriptor(usb_pipe_t *pipe,
    usb_request_type_t request_type, usb_request_recipient_t recipient,
    uint8_t descriptor_type, uint8_t descriptor_index,
    uint16_t language,
    void *buffer, size_t size)
{
        if (buffer == NULL) {
                return EBADMEM;
        }
        if (size == 0) {
                return EINVAL;
        }

        /* FIXME: proper endianness. */
        uint16_t wValue = descriptor_index | (descriptor_type << 8);

        return usb_control_request_set(pipe,
            request_type, recipient,
            USB_DEVREQ_SET_DESCRIPTOR,
            wValue, language,
            buffer, size);
}

/** Get current configuration value of USB device.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[out] configuration_value Current configuration value.
 * @return Error code.
 */
int usb_request_get_configuration(usb_pipe_t *pipe,
    uint8_t *configuration_value)
{
        uint8_t value;
        size_t actual_size;

        int rc = usb_control_request_get(pipe,
            USB_REQUEST_TYPE_STANDARD, USB_REQUEST_RECIPIENT_DEVICE,
            USB_DEVREQ_GET_CONFIGURATION,
            0, 0,
            &value, 1, &actual_size);

        if (rc != EOK) {
                return rc;
        }
        if (actual_size != 1) {
                return ELIMIT;
        }

        if (configuration_value != NULL) {
                *configuration_value = value;
        }

        return EOK;
}

/** Set configuration of USB device.
 *
 * @param pipe Control endpoint pipe (session must be already started).
 * @param configuration_value New configuration value.
 * @return Error code.
 */
int usb_request_set_configuration(usb_pipe_t *pipe,
    uint8_t configuration_value)
{
        uint16_t config_value
            = uint16_host2usb((uint16_t) configuration_value);

        return usb_control_request_set(pipe,
            USB_REQUEST_TYPE_STANDARD, USB_REQUEST_RECIPIENT_DEVICE,
            USB_DEVREQ_SET_CONFIGURATION, config_value, 0,
            NULL, 0);
}

/** Get selected alternate setting for USB interface.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[in] interface_index Interface index.
 * @param[out] alternate_setting Alternate setting for the interface.
 * @return Error code.
 */
int usb_request_get_interface(usb_pipe_t *pipe,
    uint8_t interface_index, uint8_t *alternate_setting)
{
        uint8_t value;
        size_t actual_size;

        int rc = usb_control_request_get(pipe,
            USB_REQUEST_TYPE_STANDARD, USB_REQUEST_RECIPIENT_INTERFACE,
            USB_DEVREQ_GET_INTERFACE,
            0, uint16_host2usb((uint16_t) interface_index),
            &value, 1, &actual_size);

        if (rc != EOK) {
                return rc;
        }
        if (actual_size != 1) {
                return ELIMIT;
        }

        if (alternate_setting != NULL) {
                *alternate_setting = value;
        }

        return EOK;
}

/** Select alternate setting for USB interface.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[in] interface_index Interface index.
 * @param[in] alternate_setting Alternate setting to select.
 * @return Error code.
 */
int usb_request_set_interface(usb_pipe_t *pipe,
    uint8_t interface_index, uint8_t alternate_setting)
{
        return usb_control_request_set(pipe,
            USB_REQUEST_TYPE_STANDARD, USB_REQUEST_RECIPIENT_INTERFACE,
            USB_DEVREQ_SET_INTERFACE,
            uint16_host2usb((uint16_t) alternate_setting),
            uint16_host2usb((uint16_t) interface_index),
            NULL, 0);
}

/** Get list of supported languages by USB device.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[out] languages_ptr Where to store pointer to allocated array of
 *      supported languages.
 * @param[out] languages_count Number of supported languages.
 * @return Error code.
 */
int usb_request_get_supported_languages(usb_pipe_t *pipe,
    l18_win_locales_t **languages_ptr, size_t *languages_count)
{
        int rc;

        if (languages_ptr == NULL) {
                return EBADMEM;
        }
        if (languages_count == NULL) {
                return EBADMEM;
        }

        uint8_t *string_descriptor = NULL;
        size_t string_descriptor_size = 0;
        rc = usb_request_get_descriptor_alloc(pipe,
            USB_REQUEST_TYPE_STANDARD, USB_REQUEST_RECIPIENT_DEVICE,
            USB_DESCTYPE_STRING, 0, 0,
            (void **) &string_descriptor, &string_descriptor_size);
        if (rc != EOK) {
                return rc;
        }
        if (string_descriptor_size <= 2) {
                free(string_descriptor);
                return EEMPTY;
        }
        /* Subtract first 2 bytes (length and descriptor type). */
        string_descriptor_size -= 2;

        /* Odd number of bytes - descriptor is broken? */
        if ((string_descriptor_size % 2) != 0) {
                /* FIXME: shall we return with error or silently ignore? */
                free(string_descriptor);
                return ESTALL;
        }

        size_t langs_count = string_descriptor_size / 2;
        l18_win_locales_t *langs
            = malloc(sizeof(l18_win_locales_t) * langs_count);
        if (langs == NULL) {
                free(string_descriptor);
                return ENOMEM;
        }

        size_t i;
        for (i = 0; i < langs_count; i++) {
                /* Language code from the descriptor is in USB endianness. */
                /* FIXME: is this really correct? */
                uint16_t lang_code = (string_descriptor[2 + 2 * i + 1] << 8)
                    + string_descriptor[2 + 2 * i];
                langs[i] = uint16_usb2host(lang_code);
        }

        free(string_descriptor);

        *languages_ptr = langs;
        *languages_count =langs_count;

        return EOK;
}

/** Get string (descriptor) from USB device.
 *
 * The string is returned in native encoding of the operating system.
 * For HelenOS, that is UTF-8.
 *
 * @param[in] pipe Control endpoint pipe (session must be already started).
 * @param[in] index String index (in native endianness),
 *      first index has number 1 (index from descriptors can be used directly).
 * @param[in] lang String language (in native endianness).
 * @param[out] string_ptr Where to store allocated string in native encoding.
 * @return Error code.
 */
int usb_request_get_string(usb_pipe_t *pipe,
    size_t index, l18_win_locales_t lang, char **string_ptr)
{
        if (string_ptr == NULL) {
                return EBADMEM;
        }
        /*
         * Index is actually one byte value and zero index is used
         * to retrieve list of supported languages.
         */
        if ((index < 1) || (index > 0xFF)) {
                return ERANGE;
        }
        /* Language is actually two byte value. */
        if (lang > 0xFFFF) {
                return ERANGE;
        }

        int rc;

        /* Prepare dynamically allocated variables. */
        uint8_t *string = NULL;
        wchar_t *string_chars = NULL;

        /* Get the actual descriptor. */
        size_t string_size;
        rc = usb_request_get_descriptor_alloc(pipe,
            USB_REQUEST_TYPE_STANDARD, USB_REQUEST_RECIPIENT_DEVICE,
            USB_DESCTYPE_STRING, index, uint16_host2usb(lang),
            (void **) &string, &string_size);
        if (rc != EOK) {
                goto leave;
        }

        if (string_size <= 2) {
                rc =  EEMPTY;
                goto leave;
        }
        /* Subtract first 2 bytes (length and descriptor type). */
        string_size -= 2;

        /* Odd number of bytes - descriptor is broken? */
        if ((string_size % 2) != 0) {
                /* FIXME: shall we return with error or silently ignore? */
                rc = ESTALL;
                goto leave;
        }

        size_t string_char_count = string_size / 2;
        string_chars = malloc(sizeof(wchar_t) * (string_char_count + 1));
        if (string_chars == NULL) {
                rc = ENOMEM;
                goto leave;
        }

        /*
         * Build a wide string.
         * And do not forget to set NULL terminator (string descriptors
         * do not have them).
         */
        size_t i;
        for (i = 0; i < string_char_count; i++) {
                uint16_t uni_char = (string[2 + 2 * i + 1] << 8)
                    + string[2 + 2 * i];
                string_chars[i] = uni_char;
        }
        string_chars[string_char_count] = 0;


        /* Convert to normal string. */
        char *str = wstr_to_astr(string_chars);
        if (str == NULL) {
                rc = ENOMEM;
                goto leave;
        }

        *string_ptr = str;
        rc = EOK;

leave:
        if (string != NULL) {
                free(string);
        }
        if (string_chars != NULL) {
                free(string_chars);
        }

        return rc;
}

/**
 * @}
 */