HelenOS sources

root/uspace/drv/bus/usb/xhci/isoch.c

DEFINITIONS

1. isoch_init
2. isoch_reset
3. isoch_reset_no_timer
4. isoch_reset_timer
5. timer_schedule_reset
6. isoch_fini
7. isoch_alloc_transfers
8. schedule_isochronous_trb
9. get_system_time
10. get_current_microframe
11. calc_next_mfindex
12. window_decide
13. isoch_feed_out
14. isoch_feed_out_timer
15. isoch_feed_in
16. isoch_feed_in_timer
17. isoch_schedule_out
18. isoch_schedule_in
19. isoch_handle_transfer_event

/*
 * Copyright (c) 2018 Ondrej Hlavaty, Michal Staruch
 * 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 drvusbxhci
 * @{
 */
/** @file
 * @brief The host controller endpoint management.
 */

#include <str_error.h>
#include <macros.h>

#include "endpoint.h"
#include "hw_struct/trb.h"
#include "hw_struct/regs.h"
#include "trb_ring.h"
#include "hc.h"
#include "bus.h"

#include "isoch.h"

void isoch_init(xhci_endpoint_t *ep, const usb_endpoint_descriptors_t *desc)
{
        assert(ep->base.transfer_type == USB_TRANSFER_ISOCHRONOUS);
        xhci_isoch_t *const isoch = ep->isoch;

        fibril_mutex_initialize(&isoch->guard);
        fibril_condvar_initialize(&isoch->avail);

        const xhci_hc_t *hc = bus_to_xhci_bus(ep->base.device->bus)->hc;

        /*
         * We shall cover at least twice the IST period, otherwise we will get
         * an over/underrun every time.
         */
        isoch->buffer_count = (2 * hc->ist) / ep->interval;

        /* 2 buffers are the very minimum. */
        isoch->buffer_count = max(2, isoch->buffer_count);

        usb_log_debug("[isoch] isoch setup with %zu buffers", isoch->buffer_count);
}

static void isoch_reset(xhci_endpoint_t *ep)
{
        xhci_isoch_t *const isoch = ep->isoch;
        assert(fibril_mutex_is_locked(&isoch->guard));

        isoch->dequeue = isoch->enqueue = isoch->hw_enqueue = 0;

        for (size_t i = 0; i < isoch->buffer_count; ++i) {
                isoch->transfers[i].state = ISOCH_EMPTY;
        }

        fibril_timer_clear_locked(isoch->feeding_timer);
        isoch->last_mf = -1U;
        usb_log_info("[isoch] Endpoint" XHCI_EP_FMT ": Data flow reset.",
            XHCI_EP_ARGS(*ep));
}

static void isoch_reset_no_timer(xhci_endpoint_t *ep)
{
        xhci_isoch_t *const isoch = ep->isoch;
        assert(fibril_mutex_is_locked(&isoch->guard));
        /*
         * As we cannot clear timer when we are triggered by it,
         * we have to avoid doing it in common method.
         */
        fibril_timer_clear_locked(isoch->reset_timer);
        isoch_reset(ep);
}

static void isoch_reset_timer(void *ep)
{
        xhci_isoch_t *const isoch = xhci_endpoint_get(ep)->isoch;
        fibril_mutex_lock(&isoch->guard);
        isoch_reset(ep);
        fibril_mutex_unlock(&isoch->guard);
}

/*
 * Fast transfers could trigger the reset timer before the data is processed,
 * leading into false reset.
 */
#define RESET_TIMER_DELAY 100000
static void timer_schedule_reset(xhci_endpoint_t *ep)
{
        xhci_isoch_t *const isoch = ep->isoch;
        const usec_t delay = isoch->buffer_count * ep->interval * 125 +
            RESET_TIMER_DELAY;

        fibril_timer_clear_locked(isoch->reset_timer);
        fibril_timer_set_locked(isoch->reset_timer, delay,
            isoch_reset_timer, ep);
}

void isoch_fini(xhci_endpoint_t *ep)
{
        assert(ep->base.transfer_type == USB_TRANSFER_ISOCHRONOUS);
        xhci_isoch_t *const isoch = ep->isoch;

        if (isoch->feeding_timer) {
                fibril_timer_clear(isoch->feeding_timer);
                fibril_timer_destroy(isoch->feeding_timer);
                fibril_timer_clear(isoch->reset_timer);
                fibril_timer_destroy(isoch->reset_timer);
        }

        if (isoch->transfers) {
                for (size_t i = 0; i < isoch->buffer_count; ++i)
                        dma_buffer_free(&isoch->transfers[i].data);
                free(isoch->transfers);
        }
}

/**
 * Allocate isochronous buffers. Create the feeding timer.
 */
errno_t isoch_alloc_transfers(xhci_endpoint_t *ep)
{
        assert(ep->base.transfer_type == USB_TRANSFER_ISOCHRONOUS);
        xhci_isoch_t *const isoch = ep->isoch;

        isoch->feeding_timer = fibril_timer_create(&isoch->guard);
        isoch->reset_timer = fibril_timer_create(&isoch->guard);
        if (!isoch->feeding_timer)
                return ENOMEM;

        isoch->transfers = calloc(isoch->buffer_count, sizeof(xhci_isoch_transfer_t));
        if (!isoch->transfers)
                goto err;

        for (size_t i = 0; i < isoch->buffer_count; ++i) {
                xhci_isoch_transfer_t *transfer = &isoch->transfers[i];
                if (dma_buffer_alloc(&transfer->data, ep->base.max_transfer_size)) {
                        goto err;
                }
        }

        fibril_mutex_lock(&isoch->guard);
        isoch_reset_no_timer(ep);
        fibril_mutex_unlock(&isoch->guard);

        return EOK;
err:
        isoch_fini(ep);
        return ENOMEM;
}

static errno_t schedule_isochronous_trb(xhci_endpoint_t *ep, xhci_isoch_transfer_t *it)
{
        xhci_trb_t trb;
        xhci_trb_clean(&trb);

        trb.parameter = host2xhci(64, dma_buffer_phys_base(&it->data));
        TRB_CTRL_SET_XFER_LEN(trb, it->size);
        TRB_CTRL_SET_TD_SIZE(trb, 0);
        TRB_CTRL_SET_IOC(trb, 1);
        TRB_CTRL_SET_TRB_TYPE(trb, XHCI_TRB_TYPE_ISOCH);

        // see 4.14.1 and 4.11.2.3 for the explanation, how to calculate those
        size_t tdpc = it->size / 1024 + ((it->size % 1024) ? 1 : 0);
        size_t tbc = tdpc / ep->max_burst;
        if (!tdpc % ep->max_burst)
                --tbc;
        size_t bsp = tdpc % ep->max_burst;
        size_t tlbpc = (bsp ? bsp : ep->max_burst) - 1;

        TRB_ISOCH_SET_TBC(trb, tbc);
        TRB_ISOCH_SET_TLBPC(trb, tlbpc);
        TRB_ISOCH_SET_FRAMEID(trb, (it->mfindex / 8) % 2048);

        const errno_t err = xhci_trb_ring_enqueue(&ep->ring, &trb, &it->interrupt_trb_phys);
        return err;
}

/** The number of bits the MFINDEX is stored in at HW */
#define EPOCH_BITS 14
/** The delay in usec for the epoch wrap */
#define EPOCH_DELAY 500000
/** The amount of microframes the epoch is checked for a delay */
#define EPOCH_LOW_MFINDEX 8 * 100

static inline uint64_t get_system_time()
{
        struct timespec ts;
        getuptime(&ts);
        return SEC2USEC(ts.tv_sec) + NSEC2USEC(ts.tv_nsec);
}

static inline uint64_t get_current_microframe(const xhci_hc_t *hc)
{
        const uint32_t reg_mfindex = XHCI_REG_RD(hc->rt_regs, XHCI_RT_MFINDEX);
        /*
         * If the mfindex is low and the time passed since last mfindex wrap is too
         * high, we have entered the new epoch already (and haven't received event
         * yet).
         */
        uint64_t epoch = hc->wrap_count;
        if (reg_mfindex < EPOCH_LOW_MFINDEX &&
            get_system_time() - hc->wrap_time > EPOCH_DELAY) {
                ++epoch;
        }
        return (epoch << EPOCH_BITS) + reg_mfindex;
}

static inline void calc_next_mfindex(xhci_endpoint_t *ep, xhci_isoch_transfer_t *it)
{
        xhci_isoch_t *const isoch = ep->isoch;
        if (isoch->last_mf == -1U) {
                const xhci_bus_t *bus = bus_to_xhci_bus(ep->base.device->bus);
                const xhci_hc_t *hc = bus->hc;

                /*
                 * Delay the first frame by some time to fill the buffer, but at most 10
                 * miliseconds.
                 */
                const uint64_t delay = min(isoch->buffer_count * ep->interval, 10 * 8);
                it->mfindex = get_current_microframe(hc) + 1 + delay + hc->ist;

                // Align to ESIT start boundary
                it->mfindex += ep->interval - 1;
                it->mfindex &= ~(ep->interval - 1);
        } else {
                it->mfindex = isoch->last_mf + ep->interval;
        }
}

/** 825 ms in uframes */
#define END_FRAME_DELAY   (895000 / 125)

typedef enum {
        WINDOW_TOO_SOON,
        WINDOW_INSIDE,
        WINDOW_TOO_LATE,
} window_position_t;

typedef struct {
        window_position_t position;
        uint64_t offset;
} window_decision_t;

/**
 * Decide on the position of mfindex relatively to the window specified by
 * Start Frame ID and End Frame ID. The resulting structure contains the
 * decision, and in case of the mfindex being outside, also the number of
 * uframes it's off.
 */
static inline void window_decide(window_decision_t *res, xhci_hc_t *hc,
    uint64_t mfindex)
{
        const uint64_t current_mf = get_current_microframe(hc);
        const uint64_t start = current_mf + hc->ist + 1;
        const uint64_t end = current_mf + END_FRAME_DELAY;

        if (mfindex < start) {
                res->position = WINDOW_TOO_LATE;
                res->offset = start - mfindex;
        } else if (mfindex <= end) {
                res->position = WINDOW_INSIDE;
        } else {
                res->position = WINDOW_TOO_SOON;
                res->offset = mfindex - end;
        }
}

static void isoch_feed_out_timer(void *);
static void isoch_feed_in_timer(void *);

/**
 * Schedule TRBs with filled buffers to HW. Takes filled isoch transfers and
 * pushes their TRBs to the ring.
 *
 * According to 4.11.2.5, we can't just push all TRBs we have. We must not do
 * it too late, but also not too soon.
 */
static void isoch_feed_out(xhci_endpoint_t *ep)
{
        assert(ep->base.transfer_type == USB_TRANSFER_ISOCHRONOUS);
        xhci_isoch_t *const isoch = ep->isoch;
        assert(fibril_mutex_is_locked(&isoch->guard));

        xhci_bus_t *bus = bus_to_xhci_bus(ep->base.device->bus);
        xhci_hc_t *hc = bus->hc;

        bool fed = false;

        while (isoch->transfers[isoch->hw_enqueue].state == ISOCH_FILLED) {
                xhci_isoch_transfer_t *const it = &isoch->transfers[isoch->hw_enqueue];
                usec_t delay;

                assert(it->state == ISOCH_FILLED);

                window_decision_t wd;
                window_decide(&wd, hc, it->mfindex);

                switch (wd.position) {
                case WINDOW_TOO_SOON:
                        delay = wd.offset * 125;
                        usb_log_debug("[isoch] delaying feeding buffer %zu for %lldus",
                            it - isoch->transfers, delay);
                        fibril_timer_set_locked(isoch->feeding_timer, delay,
                            isoch_feed_out_timer, ep);
                        goto out;

                case WINDOW_INSIDE:
                        usb_log_debug("[isoch] feeding buffer %zu at 0x%" PRIx64,
                            it - isoch->transfers, it->mfindex);
                        it->error = schedule_isochronous_trb(ep, it);
                        if (it->error) {
                                it->state = ISOCH_COMPLETE;
                        } else {
                                it->state = ISOCH_FED;
                                fed = true;
                        }

                        isoch->hw_enqueue = (isoch->hw_enqueue + 1) % isoch->buffer_count;
                        break;

                case WINDOW_TOO_LATE:
                        /*
                         * Missed the opportunity to schedule. Just mark this transfer as
                         * skipped.
                         */
                        usb_log_debug("[isoch] missed feeding buffer %zu at 0x%" PRIx64 " by "
                            "%" PRIu64 " uframes", it - isoch->transfers, it->mfindex, wd.offset);
                        it->state = ISOCH_COMPLETE;
                        it->error = EOK;
                        it->size = 0;

                        isoch->hw_enqueue = (isoch->hw_enqueue + 1) % isoch->buffer_count;
                        break;
                }
        }

out:
        if (fed) {
                hc_ring_ep_doorbell(ep, 0);
                /*
                 * The ring may be dead. If no event happens until the delay, reset the
                 * endpoint.
                 */
                timer_schedule_reset(ep);
        }

}

static void isoch_feed_out_timer(void *ep)
{
        xhci_isoch_t *const isoch = xhci_endpoint_get(ep)->isoch;
        fibril_mutex_lock(&isoch->guard);
        isoch_feed_out(ep);
        fibril_mutex_unlock(&isoch->guard);
}

/**
 * Schedule TRBs with empty, withdrawn buffers to HW. Takes empty isoch
 * transfers and pushes their TRBs to the ring.
 *
 * According to 4.11.2.5, we can't just push all TRBs we have. We must not do
 * it too late, but also not too soon.
 */
static void isoch_feed_in(xhci_endpoint_t *ep)
{
        assert(ep->base.transfer_type == USB_TRANSFER_ISOCHRONOUS);
        xhci_isoch_t *const isoch = ep->isoch;
        assert(fibril_mutex_is_locked(&isoch->guard));

        xhci_bus_t *bus = bus_to_xhci_bus(ep->base.device->bus);
        xhci_hc_t *hc = bus->hc;

        bool fed = false;

        while (isoch->transfers[isoch->enqueue].state <= ISOCH_FILLED) {
                xhci_isoch_transfer_t *const it = &isoch->transfers[isoch->enqueue];
                usec_t delay;

                /* IN buffers are "filled" with free space */
                if (it->state == ISOCH_EMPTY) {
                        it->size = ep->base.max_transfer_size;
                        it->state = ISOCH_FILLED;
                        calc_next_mfindex(ep, it);
                }

                window_decision_t wd;
                window_decide(&wd, hc, it->mfindex);

                switch (wd.position) {
                case WINDOW_TOO_SOON:
                        /* Not allowed to feed yet. Defer to later. */
                        delay = wd.offset * 125;
                        usb_log_debug("[isoch] delaying feeding buffer %zu for %lldus",
                            it - isoch->transfers, delay);
                        fibril_timer_set_locked(isoch->feeding_timer, delay,
                            isoch_feed_in_timer, ep);
                        goto out;
                case WINDOW_TOO_LATE:
                        usb_log_debug("[isoch] missed feeding buffer %zu at 0x%" PRIx64 " by"
                            "%" PRIu64 " uframes", it - isoch->transfers, it->mfindex, wd.offset);
                        /* Missed the opportunity to schedule. Schedule ASAP. */
                        it->mfindex += wd.offset;
                        // Align to ESIT start boundary
                        it->mfindex += ep->interval - 1;
                        it->mfindex &= ~(ep->interval - 1);

                        /* fallthrough */
                case WINDOW_INSIDE:
                        isoch->enqueue = (isoch->enqueue + 1) % isoch->buffer_count;
                        isoch->last_mf = it->mfindex;

                        usb_log_debug("[isoch] feeding buffer %zu at 0x%" PRIx64,
                            it - isoch->transfers, it->mfindex);

                        it->error = schedule_isochronous_trb(ep, it);
                        if (it->error) {
                                it->state = ISOCH_COMPLETE;
                        } else {
                                it->state = ISOCH_FED;
                                fed = true;
                        }
                        break;
                }
        }
out:

        if (fed) {
                hc_ring_ep_doorbell(ep, 0);
                /*
                 * The ring may be dead. If no event happens until the delay, reset the
                 * endpoint.
                 */
                timer_schedule_reset(ep);
        }
}

static void isoch_feed_in_timer(void *ep)
{
        xhci_isoch_t *const isoch = xhci_endpoint_get(ep)->isoch;
        fibril_mutex_lock(&isoch->guard);
        isoch_feed_in(ep);
        fibril_mutex_unlock(&isoch->guard);
}

/**
 * First, withdraw all (at least one) results left by previous transfers to
 * make room in the ring. Stop on first error.
 *
 * When there is at least one buffer free, fill it with data. Then try to feed
 * it to the xHC.
 */
errno_t isoch_schedule_out(xhci_transfer_t *transfer)
{
        errno_t err = EOK;

        xhci_endpoint_t *ep = xhci_endpoint_get(transfer->batch.ep);
        assert(ep->base.transfer_type == USB_TRANSFER_ISOCHRONOUS);
        xhci_isoch_t *const isoch = ep->isoch;

        /* This shall be already checked by endpoint */
        assert(transfer->batch.size <= ep->base.max_transfer_size);

        fibril_mutex_lock(&isoch->guard);

        /* Get the buffer to write to */
        xhci_isoch_transfer_t *it = &isoch->transfers[isoch->enqueue];

        /* Wait for the buffer to be completed */
        while (it->state == ISOCH_FED || it->state == ISOCH_FILLED) {
                fibril_condvar_wait(&isoch->avail, &isoch->guard);
                /* The enqueue ptr may have changed while sleeping */
                it = &isoch->transfers[isoch->enqueue];
        }

        isoch->enqueue = (isoch->enqueue + 1) % isoch->buffer_count;

        /* Withdraw results from previous transfers. */
        transfer->batch.transferred_size = 0;
        xhci_isoch_transfer_t *res = &isoch->transfers[isoch->dequeue];
        while (res->state == ISOCH_COMPLETE) {
                isoch->dequeue = (isoch->dequeue + 1) % isoch->buffer_count;

                res->state = ISOCH_EMPTY;
                transfer->batch.transferred_size += res->size;
                transfer->batch.error = res->error;
                if (res->error)
                        break; // Announce one error at a time

                res = &isoch->transfers[isoch->dequeue];
        }

        assert(it->state == ISOCH_EMPTY);

        /* Calculate when to schedule next transfer */
        calc_next_mfindex(ep, it);
        isoch->last_mf = it->mfindex;
        usb_log_debug("[isoch] buffer %zu will be on schedule at 0x%" PRIx64,
            it - isoch->transfers, it->mfindex);

        /* Prepare the transfer. */
        it->size = transfer->batch.size;
        memcpy(it->data.virt, transfer->batch.dma_buffer.virt, it->size);
        it->state = ISOCH_FILLED;

        fibril_timer_clear_locked(isoch->feeding_timer);
        isoch_feed_out(ep);

        fibril_mutex_unlock(&isoch->guard);

        usb_transfer_batch_finish(&transfer->batch);
        return err;
}

/**
 * IN is in fact easier than OUT. Our responsibility is just to feed all empty
 * buffers, and fetch one filled buffer from the ring.
 */
errno_t isoch_schedule_in(xhci_transfer_t *transfer)
{
        xhci_endpoint_t *ep = xhci_endpoint_get(transfer->batch.ep);
        assert(ep->base.transfer_type == USB_TRANSFER_ISOCHRONOUS);
        xhci_isoch_t *const isoch = ep->isoch;

        if (transfer->batch.size < ep->base.max_transfer_size) {
                usb_log_error("Cannot schedule an undersized isochronous transfer.");
                return ELIMIT;
        }

        fibril_mutex_lock(&isoch->guard);

        xhci_isoch_transfer_t *it = &isoch->transfers[isoch->dequeue];

        /* Wait for at least one transfer to complete. */
        while (it->state != ISOCH_COMPLETE) {
                /* First, make sure we will have something to read. */
                fibril_timer_clear_locked(isoch->feeding_timer);
                isoch_feed_in(ep);

                usb_log_debug("[isoch] waiting for buffer %zu to be completed",
                    it - isoch->transfers);
                fibril_condvar_wait(&isoch->avail, &isoch->guard);

                /* The enqueue ptr may have changed while sleeping */
                it = &isoch->transfers[isoch->dequeue];
        }

        isoch->dequeue = (isoch->dequeue + 1) % isoch->buffer_count;

        /* Withdraw results from previous transfer. */
        if (!it->error) {
                memcpy(transfer->batch.dma_buffer.virt, it->data.virt, it->size);
                transfer->batch.transferred_size = it->size;
                transfer->batch.error = it->error;
        }

        /* Prepare the empty buffer */
        it->state = ISOCH_EMPTY;

        fibril_mutex_unlock(&isoch->guard);
        usb_transfer_batch_finish(&transfer->batch);

        return EOK;
}

void isoch_handle_transfer_event(xhci_hc_t *hc, xhci_endpoint_t *ep,
    xhci_trb_t *trb)
{
        assert(ep->base.transfer_type == USB_TRANSFER_ISOCHRONOUS);
        xhci_isoch_t *const isoch = ep->isoch;

        fibril_mutex_lock(&ep->isoch->guard);

        errno_t err;
        const xhci_trb_completion_code_t completion_code = TRB_COMPLETION_CODE(*trb);

        switch (completion_code) {
        case XHCI_TRBC_RING_OVERRUN:
        case XHCI_TRBC_RING_UNDERRUN:
                /*
                 * For OUT, there was nothing to process.
                 * For IN, the buffer has overfilled.
                 * In either case, reset the ring.
                 */
                usb_log_warning("Ring over/underrun.");
                isoch_reset_no_timer(ep);
                fibril_condvar_broadcast(&ep->isoch->avail);
                fibril_mutex_unlock(&ep->isoch->guard);
                goto out;
        case XHCI_TRBC_SHORT_PACKET:
        case XHCI_TRBC_SUCCESS:
                err = EOK;
                break;
        default:
                usb_log_warning("Transfer not successfull: %u", completion_code);
                err = EIO;
                break;
        }

        /*
         * The order of delivering events is not necessarily the one we would
         * expect. It is safer to walk the list of our transfers and check
         * which one it is.
         * To minimize the amount of transfers checked, we start at dequeue pointer
         * and exit the loop as soon as the transfer is found.
         */
        bool found_mine = false;
        for (size_t i = 0, di = isoch->dequeue; i < isoch->buffer_count; ++i, ++di) {
                /* Wrap it back to 0, don't use modulo every loop traversal */
                if (di == isoch->buffer_count) {
                        di = 0;
                }

                xhci_isoch_transfer_t *const it = &isoch->transfers[di];

                if (it->state == ISOCH_FED && it->interrupt_trb_phys == trb->parameter) {
                        usb_log_debug("[isoch] buffer %zu completed", it - isoch->transfers);
                        it->state = ISOCH_COMPLETE;
                        it->size -= TRB_TRANSFER_LENGTH(*trb);
                        it->error = err;
                        found_mine = true;
                        break;
                }
        }

        if (!found_mine) {
                usb_log_warning("[isoch] A transfer event occured for unknown transfer.");
        }

        /*
         * It may happen that the driver already stopped reading (writing),
         * and our buffers are filled (empty). As QEMU (and possibly others)
         * does not send RING_UNDERRUN (OVERRUN) event, we set a timer to
         * reset it after the buffers should have been consumed. If there
         * is no issue, the timer will get restarted often enough.
         */
        timer_schedule_reset(ep);

out:
        fibril_condvar_broadcast(&ep->isoch->avail);
        fibril_mutex_unlock(&ep->isoch->guard);
}

/**
 * @}
 */