source: mainline/uspace/drv/bus/usb/xhci/commands.c@ e454d9c

/*
 * Copyright (c) 2017 Jaroslav Jindrak
 * 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 Command sending functions.
 */

#include <errno.h>
#include <str_error.h>
#include <usb/debug.h>
#include "commands.h"
#include "debug.h"
#include "hc.h"
#include "hw_struct/context.h"
#include "hw_struct/trb.h"

#define TRB_SET_TSP(trb, tsp)   (trb).control |= host2xhci(32, (((tsp) & 0x1) << 9))
#define TRB_SET_TYPE(trb, type) (trb).control |= host2xhci(32, (type) << 10)
#define TRB_SET_DC(trb, dc)     (trb).control |= host2xhci(32, (dc) << 9)
#define TRB_SET_EP(trb, ep)     (trb).control |= host2xhci(32, ((ep) & 0x5) << 16)
#define TRB_SET_STREAM(trb, st) (trb).control |= host2xhci(32, ((st) & 0xFFFF) << 16)
#define TRB_SET_SUSP(trb, susp) (trb).control |= host2xhci(32, ((susp) & 0x1) << 23)
#define TRB_SET_SLOT(trb, slot) (trb).control |= host2xhci(32, (slot) << 24)
#define TRB_SET_DEV_SPEED(trb, speed)   (trb).control |= host2xhci(32, (speed & 0xF) << 16)
#define TRB_SET_DEQUEUE_PTR(trb, dptr) (trb).parameter |= host2xhci(64, (dptr))
#define TRB_SET_ICTX(trb, phys) (trb).parameter |= host2xhci(64, (phys) & (~0xF))

#define TRB_GET_CODE(trb) XHCI_DWORD_EXTRACT((trb).status, 31, 24)
#define TRB_GET_SLOT(trb) XHCI_DWORD_EXTRACT((trb).control, 31, 24)
#define TRB_GET_PHYS(trb) (XHCI_QWORD_EXTRACT((trb).parameter, 63, 4) << 4)

/* Control functions */

static xhci_cmd_ring_t *get_cmd_ring(xhci_hc_t *hc)
{
        assert(hc);
        return &hc->cr;
}

/**
 * Initialize the command subsystem. Allocates the comand ring.
 *
 * Does not configure the CR pointer to the hardware, because the xHC will be
 * reset before starting.
 */
int xhci_init_commands(xhci_hc_t *hc)
{
        xhci_cmd_ring_t *cr = get_cmd_ring(hc);
        int err;

        if ((err = xhci_trb_ring_init(&cr->trb_ring, 0)))
                return err;

        fibril_mutex_initialize(&cr->guard);
        fibril_condvar_initialize(&cr->state_cv);
        fibril_condvar_initialize(&cr->stopped_cv);

        list_initialize(&cr->cmd_list);

        cr->state = XHCI_CR_STATE_OPEN;

        return EOK;
}

/**
 * Finish the command subsystem. Stops the hardware from running commands, then
 * deallocates the ring.
 */
void xhci_fini_commands(xhci_hc_t *hc)
{
        assert(hc);
        xhci_stop_command_ring(hc);

        xhci_cmd_ring_t *cr = get_cmd_ring(hc);

        fibril_mutex_lock(&cr->guard);
        xhci_trb_ring_fini(&cr->trb_ring);
        fibril_mutex_unlock(&cr->guard);
}

/**
 * Initialize a command structure for the given command.
 */
void xhci_cmd_init(xhci_cmd_t *cmd, xhci_cmd_type_t type)
{
        memset(cmd, 0, sizeof(*cmd));

        link_initialize(&cmd->_header.link);

        fibril_mutex_initialize(&cmd->_header.completed_mtx);
        fibril_condvar_initialize(&cmd->_header.completed_cv);

        cmd->_header.cmd = type;
}

/**
 * Finish the command structure. Some command invocation includes allocating
 * a context structure. To have the convenience in calling commands, this
 * method deallocates all resources.
 */
void xhci_cmd_fini(xhci_cmd_t *cmd)
{
        list_remove(&cmd->_header.link);

        dma_buffer_free(&cmd->input_ctx);
        dma_buffer_free(&cmd->bandwidth_ctx);

        if (cmd->_header.async) {
                free(cmd);
        }
}

/**
 * Find a command issued by TRB at @c phys inside the command list.
 *
 * Call with guard locked only.
 */
static inline xhci_cmd_t *find_command(xhci_hc_t *hc, uint64_t phys)
{
        xhci_cmd_ring_t *cr = get_cmd_ring(hc);
        assert(fibril_mutex_is_locked(&cr->guard));

        link_t *cmd_link = list_first(&cr->cmd_list);

        while (cmd_link != NULL) {
                xhci_cmd_t *cmd = list_get_instance(cmd_link, xhci_cmd_t, _header.link);

                if (cmd->_header.trb_phys == phys)
                        break;

                cmd_link = list_next(cmd_link, &cr->cmd_list);
        }

        return cmd_link ? list_get_instance(cmd_link, xhci_cmd_t, _header.link)
                : NULL;
}

static void cr_set_state(xhci_cmd_ring_t *cr, xhci_cr_state_t state)
{
        assert(fibril_mutex_is_locked(&cr->guard));

        cr->state = state;
        if (state == XHCI_CR_STATE_OPEN
            || state == XHCI_CR_STATE_CLOSED)
                fibril_condvar_broadcast(&cr->state_cv);
}

static int wait_for_ring_open(xhci_cmd_ring_t *cr)
{
        assert(fibril_mutex_is_locked(&cr->guard));

        while (true) {
                switch (cr->state) {
                case XHCI_CR_STATE_CHANGING:
                case XHCI_CR_STATE_FULL:
                        fibril_condvar_wait(&cr->state_cv, &cr->guard);
                        break;
                case XHCI_CR_STATE_OPEN:
                        return EOK;
                case XHCI_CR_STATE_CLOSED:
                        return ENAK;
                }
        }
}

/**
 * Enqueue a command on the TRB ring. Ring the doorbell to initiate processing.
 * Register the command as waiting for completion inside the command list.
 */
static inline int enqueue_command(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        xhci_cmd_ring_t *cr = get_cmd_ring(hc);
        assert(cmd);

        fibril_mutex_lock(&cr->guard);

        if (wait_for_ring_open(cr)) {
                fibril_mutex_unlock(&cr->guard);
                return ENAK;
        }

        usb_log_debug("Sending command %s", xhci_trb_str_type(TRB_TYPE(cmd->_header.trb)));

        list_append(&cmd->_header.link, &cr->cmd_list);

        int err = EOK;
        while (err == EOK) {
                err = xhci_trb_ring_enqueue(&cr->trb_ring,
                    &cmd->_header.trb, &cmd->_header.trb_phys);
                if (err != EAGAIN)
                        break;

                cr_set_state(cr, XHCI_CR_STATE_FULL);
                err = wait_for_ring_open(cr);
        }

        if (err == EOK)
                hc_ring_doorbell(hc, 0, 0);

        fibril_mutex_unlock(&cr->guard);

        return err;
}

/**
 * Stop the command ring. Stop processing commands, block issuing new ones.
 * Wait until hardware acknowledges it is stopped.
 */
void xhci_stop_command_ring(xhci_hc_t *hc)
{
        xhci_cmd_ring_t *cr = get_cmd_ring(hc);

        fibril_mutex_lock(&cr->guard);

        // Prevent others from starting CR again.
        cr_set_state(cr, XHCI_CR_STATE_CLOSED);

        /* Some systems, inc. QEMU, need whole 64-bit qword to be written */
        XHCI_REG_SET(hc->op_regs, XHCI_OP_CS, 1);
        XHCI_REG_SET(hc->op_regs, XHCI_OP_CRCR_HI, 0);

        while (XHCI_REG_RD(hc->op_regs, XHCI_OP_CRR))
                fibril_condvar_wait(&cr->stopped_cv, &cr->guard);

        fibril_mutex_unlock(&cr->guard);
}

/**
 * Abort currently processed command. Note that it is only aborted when the
 * command is "blocking" - see section 4.6.1.2 of xHCI spec.
 */
static void abort_command_ring(xhci_hc_t *hc)
{
        /* Some systems, inc. QEMU, need whole 64-bit qword to be written */
        XHCI_REG_SET(hc->op_regs, XHCI_OP_CA, 1);
        XHCI_REG_SET(hc->op_regs, XHCI_OP_CRCR_HI, 0);
}

static const char *trb_codes [] = {
#define TRBC(t) [XHCI_TRBC_##t] = #t
        TRBC(INVALID),
        TRBC(SUCCESS),
        TRBC(DATA_BUFFER_ERROR),
        TRBC(BABBLE_DETECTED_ERROR),
        TRBC(USB_TRANSACTION_ERROR),
        TRBC(TRB_ERROR),
        TRBC(STALL_ERROR),
        TRBC(RESOURCE_ERROR),
        TRBC(BANDWIDTH_ERROR),
        TRBC(NO_SLOTS_ERROR),
        TRBC(INVALID_STREAM_ERROR),
        TRBC(SLOT_NOT_ENABLED_ERROR),
        TRBC(EP_NOT_ENABLED_ERROR),
        TRBC(SHORT_PACKET),
        TRBC(RING_UNDERRUN),
        TRBC(RING_OVERRUN),
        TRBC(VF_EVENT_RING_FULL),
        TRBC(PARAMETER_ERROR),
        TRBC(BANDWIDTH_OVERRUN_ERROR),
        TRBC(CONTEXT_STATE_ERROR),
        TRBC(NO_PING_RESPONSE_ERROR),
        TRBC(EVENT_RING_FULL_ERROR),
        TRBC(INCOMPATIBLE_DEVICE_ERROR),
        TRBC(MISSED_SERVICE_ERROR),
        TRBC(COMMAND_RING_STOPPED),
        TRBC(COMMAND_ABORTED),
        TRBC(STOPPED),
        TRBC(STOPPED_LENGTH_INVALID),
        TRBC(STOPPED_SHORT_PACKET),
        TRBC(MAX_EXIT_LATENCY_TOO_LARGE_ERROR),
        [30] = "<reserved>",
        TRBC(ISOCH_BUFFER_OVERRUN),
        TRBC(EVENT_LOST_ERROR),
        TRBC(UNDEFINED_ERROR),
        TRBC(INVALID_STREAM_ID_ERROR),
        TRBC(SECONDARY_BANDWIDTH_ERROR),
        TRBC(SPLIT_TRANSACTION_ERROR),
        [XHCI_TRBC_MAX] = NULL
#undef TRBC
};

/**
 * Report an error according to command completion code.
 */
static void report_error(int code)
{
        if (code < XHCI_TRBC_MAX && trb_codes[code] != NULL)
                usb_log_error("Command resulted in error: %s.", trb_codes[code]);
        else
                usb_log_error("Command resulted in reserved or vendor specific error.");
}

/**
 * Handle a command completion. Feed the fibril waiting for result.
 *
 * @param trb The COMMAND_COMPLETION TRB found in event ring.
 */
int xhci_handle_command_completion(xhci_hc_t *hc, xhci_trb_t *trb)
{
        xhci_cmd_ring_t *cr = get_cmd_ring(hc);
        assert(trb);

        fibril_mutex_lock(&cr->guard);

        int code = TRB_GET_CODE(*trb);

        if (code == XHCI_TRBC_COMMAND_RING_STOPPED) {
                /* This can either mean that the ring is being stopped, or
                 * a command was aborted. In either way, wake threads waiting
                 * on stopped_cv.
                 *
                 * Note that we need to hold mutex, because we must be sure the
                 * requesting thread is waiting inside the CV.
                 */
                usb_log_debug("Command ring stopped.");
                fibril_condvar_broadcast(&cr->stopped_cv);
                fibril_mutex_unlock(&cr->guard);
                return EOK;
        }

        const uint64_t phys = TRB_GET_PHYS(*trb);
        xhci_trb_ring_update_dequeue(&cr->trb_ring, phys);

        if (cr->state == XHCI_CR_STATE_FULL)
                cr_set_state(cr, XHCI_CR_STATE_OPEN);

        xhci_cmd_t *command = find_command(hc, phys);
        if (command == NULL) {
                usb_log_error("No command struct for completion event found.");

                if (code != XHCI_TRBC_SUCCESS)
                        report_error(code);

                return EOK;
        }

        list_remove(&command->_header.link);

        /* Semantics of NO_OP_CMD is that success is marked as a TRB error. */
        if (command->_header.cmd == XHCI_CMD_NO_OP && code == XHCI_TRBC_TRB_ERROR)
                code = XHCI_TRBC_SUCCESS;

        command->status = code;
        command->slot_id = TRB_GET_SLOT(*trb);

        usb_log_debug("Completed command %s",
            xhci_trb_str_type(TRB_TYPE(command->_header.trb)));

        if (code != XHCI_TRBC_SUCCESS) {
                report_error(code);
                xhci_dump_trb(&command->_header.trb);
        }

        fibril_mutex_unlock(&cr->guard);

        fibril_mutex_lock(&command->_header.completed_mtx);
        command->_header.completed = true;
        fibril_condvar_broadcast(&command->_header.completed_cv);
        fibril_mutex_unlock(&command->_header.completed_mtx);

        if (command->_header.async) {
                /* Free the command and other DS upon completion. */
                xhci_cmd_fini(command);
        }

        return EOK;
}

/* Command-issuing functions */

static int no_op_cmd(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        assert(hc);

        xhci_trb_clean(&cmd->_header.trb);

        TRB_SET_TYPE(cmd->_header.trb, XHCI_TRB_TYPE_NO_OP_CMD);

        return enqueue_command(hc, cmd);
}

static int enable_slot_cmd(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        assert(hc);

        xhci_trb_clean(&cmd->_header.trb);

        TRB_SET_TYPE(cmd->_header.trb, XHCI_TRB_TYPE_ENABLE_SLOT_CMD);
        cmd->_header.trb.control |=
            host2xhci(32, XHCI_REG_RD(hc->xecp, XHCI_EC_SP_SLOT_TYPE) << 16);

        return enqueue_command(hc, cmd);
}

static int disable_slot_cmd(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        assert(hc);
        assert(cmd);

        xhci_trb_clean(&cmd->_header.trb);

        TRB_SET_TYPE(cmd->_header.trb, XHCI_TRB_TYPE_DISABLE_SLOT_CMD);
        TRB_SET_SLOT(cmd->_header.trb, cmd->slot_id);

        return enqueue_command(hc, cmd);
}

static int address_device_cmd(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        assert(hc);
        assert(cmd);
        assert(dma_buffer_is_set(&cmd->input_ctx));

        /**
         * TODO: Requirements for this command:
         *           dcbaa[slot_id] is properly sized and initialized
         *           ictx has valids slot context and endpoint 0, all
         *           other should be ignored at this point (see section 4.6.5).
         */

        xhci_trb_clean(&cmd->_header.trb);

        TRB_SET_ICTX(cmd->_header.trb, cmd->input_ctx.phys);

        /**
         * Note: According to section 6.4.3.4, we can set the 9th bit
         *       of the control field of the trb (BSR) to 1 and then the xHC
         *       will not issue the SET_ADDRESS request to the USB device.
         *       This can be used to provide compatibility with legacy USB devices
         *       that require their device descriptor to be read before such request.
         */
        TRB_SET_TYPE(cmd->_header.trb, XHCI_TRB_TYPE_ADDRESS_DEVICE_CMD);
        TRB_SET_SLOT(cmd->_header.trb, cmd->slot_id);

        return enqueue_command(hc, cmd);
}

static int configure_endpoint_cmd(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        assert(hc);
        assert(cmd);

        xhci_trb_clean(&cmd->_header.trb);

        if (!cmd->deconfigure) {
                /* If the DC flag is on, input context is not evaluated. */
                assert(dma_buffer_is_set(&cmd->input_ctx));

                TRB_SET_ICTX(cmd->_header.trb, cmd->input_ctx.phys);
        }

        TRB_SET_TYPE(cmd->_header.trb, XHCI_TRB_TYPE_CONFIGURE_ENDPOINT_CMD);
        TRB_SET_SLOT(cmd->_header.trb, cmd->slot_id);
        TRB_SET_DC(cmd->_header.trb, cmd->deconfigure);

        return enqueue_command(hc, cmd);
}

static int evaluate_context_cmd(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        assert(hc);
        assert(cmd);
        assert(dma_buffer_is_set(&cmd->input_ctx));

        /**
         * Note: All Drop Context flags of the input context shall be 0,
         *       all Add Context flags shall be initialize to indicate IDs
         *       of the contexts affected by the command.
         *       Refer to sections 6.2.2.3 and 6.3.3.3 for further info.
         */
        xhci_trb_clean(&cmd->_header.trb);

        TRB_SET_ICTX(cmd->_header.trb, cmd->input_ctx.phys);

        TRB_SET_TYPE(cmd->_header.trb, XHCI_TRB_TYPE_EVALUATE_CONTEXT_CMD);
        TRB_SET_SLOT(cmd->_header.trb, cmd->slot_id);

        return enqueue_command(hc, cmd);
}

static int reset_endpoint_cmd(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        assert(hc);
        assert(cmd);

        xhci_trb_clean(&cmd->_header.trb);

        TRB_SET_TYPE(cmd->_header.trb, XHCI_TRB_TYPE_RESET_ENDPOINT_CMD);
        TRB_SET_TSP(cmd->_header.trb, cmd->tsp);
        TRB_SET_EP(cmd->_header.trb, cmd->endpoint_id);
        TRB_SET_SLOT(cmd->_header.trb, cmd->slot_id);

        return enqueue_command(hc, cmd);
}

static int stop_endpoint_cmd(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        assert(hc);
        assert(cmd);

        xhci_trb_clean(&cmd->_header.trb);

        TRB_SET_TYPE(cmd->_header.trb, XHCI_TRB_TYPE_STOP_ENDPOINT_CMD);
        TRB_SET_EP(cmd->_header.trb, cmd->endpoint_id);
        TRB_SET_SUSP(cmd->_header.trb, cmd->susp);
        TRB_SET_SLOT(cmd->_header.trb, cmd->slot_id);

        return enqueue_command(hc, cmd);
}

static int set_tr_dequeue_pointer_cmd(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        assert(hc);
        assert(cmd);

        xhci_trb_clean(&cmd->_header.trb);

        TRB_SET_TYPE(cmd->_header.trb, XHCI_TRB_TYPE_SET_TR_DEQUEUE_POINTER_CMD);
        TRB_SET_EP(cmd->_header.trb, cmd->endpoint_id);
        TRB_SET_STREAM(cmd->_header.trb, cmd->stream_id);
        TRB_SET_SLOT(cmd->_header.trb, cmd->slot_id);
        TRB_SET_DEQUEUE_PTR(cmd->_header.trb, cmd->dequeue_ptr);

        return enqueue_command(hc, cmd);
}

static int reset_device_cmd(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        assert(hc);
        assert(cmd);

        xhci_trb_clean(&cmd->_header.trb);

        TRB_SET_TYPE(cmd->_header.trb, XHCI_TRB_TYPE_RESET_DEVICE_CMD);
        TRB_SET_SLOT(cmd->_header.trb, cmd->slot_id);

        return enqueue_command(hc, cmd);
}

static int get_port_bandwidth_cmd(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        assert(hc);
        assert(cmd);

        xhci_trb_clean(&cmd->_header.trb);

        TRB_SET_ICTX(cmd->_header.trb, cmd->bandwidth_ctx.phys);

        TRB_SET_TYPE(cmd->_header.trb, XHCI_TRB_TYPE_GET_PORT_BANDWIDTH_CMD);
        TRB_SET_SLOT(cmd->_header.trb, cmd->slot_id);
        TRB_SET_DEV_SPEED(cmd->_header.trb, cmd->device_speed);

        return enqueue_command(hc, cmd);
}

/* The table of command-issuing functions. */

typedef int (*cmd_handler) (xhci_hc_t *hc, xhci_cmd_t *cmd);

static cmd_handler cmd_handlers [] = {
        [XHCI_CMD_ENABLE_SLOT] = enable_slot_cmd,
        [XHCI_CMD_DISABLE_SLOT] = disable_slot_cmd,
        [XHCI_CMD_ADDRESS_DEVICE] = address_device_cmd,
        [XHCI_CMD_CONFIGURE_ENDPOINT] = configure_endpoint_cmd,
        [XHCI_CMD_EVALUATE_CONTEXT] = evaluate_context_cmd,
        [XHCI_CMD_RESET_ENDPOINT] = reset_endpoint_cmd,
        [XHCI_CMD_STOP_ENDPOINT] = stop_endpoint_cmd,
        [XHCI_CMD_SET_TR_DEQUEUE_POINTER] = set_tr_dequeue_pointer_cmd,
        [XHCI_CMD_RESET_DEVICE] = reset_device_cmd,
        [XHCI_CMD_FORCE_EVENT] = NULL,
        [XHCI_CMD_NEGOTIATE_BANDWIDTH] = NULL,
        [XHCI_CMD_SET_LATENCY_TOLERANCE_VALUE] = NULL,
        [XHCI_CMD_GET_PORT_BANDWIDTH] = get_port_bandwidth_cmd,
        [XHCI_CMD_FORCE_HEADER] = NULL,
        [XHCI_CMD_NO_OP] = no_op_cmd
};

/**
 * Try to abort currently processed command. This is tricky, because
 * calling fibril is not necessarily the one which issued the blocked command.
 * Also, the trickiness intensifies by the fact that stopping a CR is denoted by
 * event, which is again handled in different fibril. but, once we go to sleep
 * on waiting for that event, another fibril may wake up and try to abort the
 * blocked command.
 *
 * So, we mark the command ring as being restarted, wait for it to stop, and
 * then start it again. If there was a blocked command, it will be satisfied by
 * COMMAND_ABORTED event.
 */
static int try_abort_current_command(xhci_hc_t *hc)
{
        xhci_cmd_ring_t *cr = get_cmd_ring(hc);

        fibril_mutex_lock(&cr->guard);

        if (cr->state == XHCI_CR_STATE_CLOSED) {
                fibril_mutex_unlock(&cr->guard);
                return ENAK;
        }

        if (cr->state == XHCI_CR_STATE_CHANGING) {
                fibril_mutex_unlock(&cr->guard);
                return EOK;
        }

        usb_log_error("Timeout while waiting for command: aborting current command.");

        cr_set_state(cr, XHCI_CR_STATE_CHANGING);

        abort_command_ring(hc);

        fibril_condvar_wait_timeout(&cr->stopped_cv, &cr->guard, XHCI_CR_ABORT_TIMEOUT);

        if (XHCI_REG_RD(hc->op_regs, XHCI_OP_CRR)) {
                /* 4.6.1.2, implementation note
                 * Assume there are larger problems with HC and
                 * reset it.
                 */
                usb_log_error("Command didn't abort.");

                cr_set_state(cr, XHCI_CR_STATE_CLOSED);

                // TODO: Reset HC completely.
                // Don't forget to somehow complete all commands with error.

                fibril_mutex_unlock(&cr->guard);
                return ENAK;
        }

        cr_set_state(cr, XHCI_CR_STATE_OPEN);

        fibril_mutex_unlock(&cr->guard);

        usb_log_error("Command ring stopped. Starting again.");
        hc_ring_doorbell(hc, 0, 0);

        return EOK;
}

/**
 * Wait, until the command is completed. The completion is triggered by
 * COMMAND_COMPLETION event. As we do not want to rely on HW completing the
 * command in timely manner, we timeout. Note that we can't just return an
 * error after the timeout pass - it may be other command blocking the ring,
 * and ours can be completed afterwards. Therefore, it is not guaranteed that
 * this function will return in XHCI_COMMAND_TIMEOUT. It will continue waiting
 * until COMMAND_COMPLETION event arrives.
 */
static int wait_for_cmd_completion(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        int rv = EOK;

        if (fibril_get_id() == hc->event_handler) {
                usb_log_error("Deadlock detected in waiting for command.");
                abort();
        }

        fibril_mutex_lock(&cmd->_header.completed_mtx);
        while (!cmd->_header.completed) {

                rv = fibril_condvar_wait_timeout(&cmd->_header.completed_cv,
                    &cmd->_header.completed_mtx, XHCI_COMMAND_TIMEOUT);

                /* The waiting timed out. Current command (not necessarily
                 * ours) is probably blocked.
                 */
                if (!cmd->_header.completed && rv == ETIMEOUT) {
                        fibril_mutex_unlock(&cmd->_header.completed_mtx);

                        rv = try_abort_current_command(hc);
                        if (rv)
                                return rv;

                        fibril_mutex_lock(&cmd->_header.completed_mtx);
                }
        }
        fibril_mutex_unlock(&cmd->_header.completed_mtx);

        return rv;
}

/**
 * Issue command and block the current fibril until it is completed or timeout
 * expires. Nothing is deallocated. Caller should always execute `xhci_cmd_fini`.
 */
int xhci_cmd_sync(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        assert(hc);
        assert(cmd);

        int err;

        if (!cmd_handlers[cmd->_header.cmd]) {
                /* Handler not implemented. */
                return ENOTSUP;
        }

        if ((err = cmd_handlers[cmd->_header.cmd](hc, cmd))) {
                /* Command could not be issued. */
                return err;
        }

        if ((err = wait_for_cmd_completion(hc, cmd))) {
                /* Command failed. */
                return err;
        }

        switch (cmd->status) {
        case XHCI_TRBC_SUCCESS:
                return EOK;
        case XHCI_TRBC_USB_TRANSACTION_ERROR:
                return ESTALL;
        case XHCI_TRBC_RESOURCE_ERROR:
        case XHCI_TRBC_BANDWIDTH_ERROR:
        case XHCI_TRBC_NO_SLOTS_ERROR:
                return ELIMIT;
        case XHCI_TRBC_SLOT_NOT_ENABLED_ERROR:
                return ENOENT;
        default:
                return EINVAL;
        }
}

/**
 * Does the same thing as `xhci_cmd_sync` and executes `xhci_cmd_fini`. This
 * is a useful shorthand for issuing commands without out parameters.
 */
int xhci_cmd_sync_fini(xhci_hc_t *hc, xhci_cmd_t *cmd)
{
        const int err = xhci_cmd_sync(hc, cmd);
        xhci_cmd_fini(cmd);

        return err;
}

/**
 * Does the same thing as `xhci_cmd_sync_fini` without blocking the current
 * fibril. The command is copied to stack memory and `fini` is called upon its completion.
 */
int xhci_cmd_async_fini(xhci_hc_t *hc, xhci_cmd_t *stack_cmd)
{
        assert(hc);
        assert(stack_cmd);

        /* Save the command for later. */
        xhci_cmd_t *heap_cmd = (xhci_cmd_t *) malloc(sizeof(xhci_cmd_t));
        if (!heap_cmd) {
                return ENOMEM;
        }

        /* TODO: Is this good for the mutex and the condvar? */
        memcpy(heap_cmd, stack_cmd, sizeof(xhci_cmd_t));
        heap_cmd->_header.async = true;

        /* Issue the command. */
        int err;

        if (!cmd_handlers[heap_cmd->_header.cmd]) {
                /* Handler not implemented. */
                err = ENOTSUP;
                goto err_heap_cmd;
        }

        if ((err = cmd_handlers[heap_cmd->_header.cmd](hc, heap_cmd))) {
                /* Command could not be issued. */
                goto err_heap_cmd;
        }

        return EOK;

err_heap_cmd:
        free(heap_cmd);
        return err;
}

/**
 * @}
 */