hw/misc/goldfish_sync.c - qemu-android - Git at Google

 /* Copyright (C) 2016 The Android Open Source Project
 **
 ** This software is licensed under the terms of the GNU General Public
 ** License version 2, as published by the Free Software Foundation, and
 ** may be copied, distributed, and modified under those terms.
 **
 ** This program is distributed in the hope that it will be useful,
 ** but WITHOUT ANY WARRANTY; without even the implied warranty of
 ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 ** GNU General Public License for more details.
 */

 #include "qemu/osdep.h"
 #include "hw/hw.h"
 #include "hw/sysbus.h"
 #include "qemu-common.h"
 #include "qemu/error-report.h"
 #include "qemu/main-loop.h"
 #include "trace.h"
 #include "hw/misc/goldfish_sync.h"

 #include <assert.h>

 // TODO(digit): Plug better logging for Android emulator.
 #define DPRINT(...)

 // Goldfish sync commands=======================================================

 // Batch command formats:
 // Host->guest:
 struct goldfish_sync_batch_cmd {
     // sorted by size for alignment
     uint64_t handle;
     uint64_t hostcmd_handle;
     uint32_t cmd;
     uint32_t time_arg;
 };

 // guest->host:
 struct goldfish_sync_batch_guestcmd {
     uint64_t host_command; // uint64_t for alignment
     uint64_t glsync_handle;
     uint64_t thread_handle;
     uint64_t guest_timeline_handle;
 };

 // This is a suffix of batch cmd.
 // The purpose of the "pending_cmd" variant
 // is so we can queue up several batch commands
 // in the same IRQ level.
 struct goldfish_sync_pending_cmd {
     uint64_t handle;
     uint64_t hostcmd_handle;
     uint32_t cmd;
     uint32_t time_arg;
     struct goldfish_sync_pending_cmd* next;
 };

 // Command numbers that can only be sent from the guest to the device.
 #define SYNC_GUEST_CMD_READY 0
 #define SYNC_GUEST_CMD_TRIGGER_HOST_WAIT 5

 // The register layout is:

 #define SYNC_REG_BATCH_COMMAND                0x00 // host->guest batch commands
 #define SYNC_REG_BATCH_GUESTCOMMAND           0x04 // guest->host batch commands
 #define SYNC_REG_BATCH_COMMAND_ADDR           0x08 // communicate physical address of host->guest batch commands
 #define SYNC_REG_BATCH_COMMAND_ADDR_HIGH      0x0c // 64-bit part
 #define SYNC_REG_BATCH_GUESTCOMMAND_ADDR      0x10 // communicate physical address of guest->host commands
 #define SYNC_REG_BATCH_GUESTCOMMAND_ADDR_HIGH 0x14 // 64-bit part
 #define SYNC_REG_INIT                         0x18 // to signal that the device has been detected by the kernel

 // The goldfish sync device is represented by the goldfish_sync_state struct.
 // Besides the machinery necessary to do I/O with the guest:
 // |pending|: a linked list of |goldfish_sync_pending_cmd|'s
 // that need to be processed by the kernel.
 // |first_pending_cmd|: maintains a pointer to the earliest pending command
 // that needs to be sent. We plan to process pending commands in the same
 // order in which they were received.
 // |current|: Intermediate value that represents a popped-off pending
 // command.
 // |batch_cmd_addr|: Physical memory address where we write the details
 // of each command that comes in from the host. We also read replies
 // from the same address (if applicable)
 // |batch_guestcmd_addr|: Physical memory address where we read the
 // details of each command that comes in from the guest.
 // |ops|: Callbacks to other areas of the emulator that need to be
 // triggered upon reading a guest->host command.
 struct goldfish_sync_state {
     SysBusDevice parent;
     MemoryRegion iomem;
     qemu_irq irq;

     struct goldfish_sync_pending_cmd* pending;
     struct goldfish_sync_pending_cmd* first_pending_cmd;
     struct goldfish_sync_pending_cmd* current;

     uint64_t batch_cmd_addr;
     uint64_t batch_guestcmd_addr;

     struct goldfish_sync_ops* ops;
 };

 static struct goldfish_sync_state* s_goldfish_sync_dev;

 static const GoldfishSyncServiceOps* service_ops = NULL;

 void goldfish_sync_set_service_ops(const GoldfishSyncServiceOps *ops) {
     service_ops = ops;
 }

 // Command list operations======================================================

 static struct goldfish_sync_pending_cmd*
 goldfish_sync_new_cmd(void) {
     struct goldfish_sync_pending_cmd* res;
     res = g_malloc0(sizeof(struct goldfish_sync_pending_cmd));
     return res;
 }

 static void
 goldfish_sync_free_cmd(struct goldfish_sync_pending_cmd* cmd) {
     g_free(cmd);
 }

 static void
 goldfish_sync_push_cmd(struct goldfish_sync_state* state,
                        struct goldfish_sync_pending_cmd* cmd) {

     cmd->next = NULL;

     if (state->pending) {
         state->pending->next = cmd;
     }

     // We need to reset first_pending_cmd if
     // the list was empty to start with.
     if (!state->pending) {
         state->first_pending_cmd = cmd;
     }

     state->pending = cmd;
 }

 static struct goldfish_sync_pending_cmd*
 goldfish_sync_pop_first_cmd(struct goldfish_sync_state* state) {

     struct goldfish_sync_pending_cmd* popped =
         state->first_pending_cmd;

     // Update list structure as follows:
     // 1. Don't do anything if its already empty.
     if (!popped) return NULL;

     // 2. Update first_pending_cmd and pending fields,
     // changing list structure to reflect the change.
     state->first_pending_cmd = popped->next;
     if (state->pending == popped) state->pending = NULL;

     return popped;
 }

 static void goldfish_sync_clear_pending(struct goldfish_sync_state* state) {
     struct goldfish_sync_pending_cmd* curr =
         state->pending;

     while (curr) {
         struct goldfish_sync_pending_cmd* tmp = curr;
         curr = curr->next;
         goldfish_sync_free_cmd(tmp);
     }

     state->pending = NULL;
     state->first_pending_cmd = NULL;
 }

 static void goldfish_sync_reset_device(struct goldfish_sync_state* state) {
     goldfish_sync_clear_pending(state);
     qemu_set_irq(state->irq, 0);
 }

 // Callbacks and hw_funcs struct================================================

 // goldfish_sync_send_command does the actual work of setting up
 // the sync device registers, causing IRQ blip,
 // and waiting for + reading back results from the guest
 // (if appplicable)
 void goldfish_sync_send_command(uint32_t cmd,
                                 uint64_t handle,
                                 uint32_t time_arg,
                                 uint64_t hostcmd_handle) {

     struct goldfish_sync_state* s;
     struct goldfish_sync_pending_cmd* to_send;
     s = s_goldfish_sync_dev;

     DPRINT("incoming cmd. "
            "cmd=%u "
            "handle=0x%llx "
            "time_arg=%u "
            "hostcmd_handle=0x%llx",
            cmd, handle, time_arg, hostcmd_handle);

     to_send = goldfish_sync_new_cmd();
     to_send->cmd = cmd;
     to_send->handle = handle;
     to_send->time_arg = time_arg;
     to_send->hostcmd_handle = hostcmd_handle;

     goldfish_sync_push_cmd(s, to_send);

     qemu_set_irq(s->irq, 1);

     DPRINT("Exit");
 }

 #define TYPE_GOLDFISH_SYNC "goldfish_sync"
 #define GOLDFISH_SYNC(obj) \
     OBJECT_CHECK(struct goldfish_sync_state, (obj), TYPE_GOLDFISH_SYNC)

 static uint64_t
 goldfish_sync_read(void *opaque,
                    hwaddr offset,
                    unsigned size) {

     DPRINT("opaque=%p offset=0x%lx sz=0x%x", opaque, offset, size);

     struct goldfish_sync_state* s = opaque;
     struct goldfish_sync_batch_cmd* curr_batch_cmd;

     switch (offset) {
     // SYNC_REG_BATCH_COMMAND read:
     // This is triggered by the kernel whenever we are processing
     // any host->guest sync command, such as timeline increment.
     // The role of this part is to pass command info (in the struct
     // |goldfish_sync_batch_cmd|'s to the guest where the commands
     // are actually run.
     //
     // SYNC_REG_BATCH_COMMAND is the first thing
     // to happen on a IRQ level raise, and will continue re-issuing
     // throughout IRQ active high, until all pending commands on the
     // host (the linked list) are processed. At that point, IRQ
     // is lowered.
     case SYNC_REG_BATCH_COMMAND:
         s->current = goldfish_sync_pop_first_cmd(s);
         if (!s->current) {
             DPRINT("Out of pending commands. Lower IRQ.");
             struct goldfish_sync_batch_cmd quit_cmd = {
                 .cmd = 0, .handle = 0, .time_arg = 0, .hostcmd_handle = 0
             };
             cpu_physical_memory_write(s->batch_cmd_addr,
                                       (void*)&quit_cmd,
                                       sizeof(struct goldfish_sync_batch_cmd));
             qemu_set_irq(s->irq, 0);
             return 0;
         } else {
             // goldfish_sync_batch_cmd is a prefix of
             // goldfish_sync_pending_cmd, so we can avoid a copy.
             curr_batch_cmd = (struct goldfish_sync_batch_cmd*)(s->current);
             DPRINT("read SYNC_REG_BATCH_COMMAND. writing to batch addr: "
                    "cmd=%u handle=0x%llx time_arg=%u hostcmd_handle=0x%llx",
                    curr_batch_cmd->cmd,
                    curr_batch_cmd->handle,
                    curr_batch_cmd->time_arg,
                    curr_batch_cmd->hostcmd_handle);
             cpu_physical_memory_write(s->batch_cmd_addr,
                                       (void*)curr_batch_cmd,
                                       sizeof(struct goldfish_sync_batch_cmd));
             goldfish_sync_free_cmd(s->current);
             s->current = NULL;
         }
         DPRINT("done SYNC_REG_BATCH_COMMAND. returning result val?");
         return 0;
     // SYNC_REG_BATCH_(GUEST)COMMAND_ADDR(_HIGH) read:
     // Used solely to verify that the |s->batch_cmd_addr| on the host
     // is the same physical address as the corresponding one
     // on the guest.
     case SYNC_REG_BATCH_COMMAND_ADDR:
         return (uint64_t)(uint32_t)(s->batch_cmd_addr);
     case SYNC_REG_BATCH_COMMAND_ADDR_HIGH:
         return (uint64_t)(uint32_t)(s->batch_cmd_addr >> 32);
     case SYNC_REG_BATCH_GUESTCOMMAND_ADDR:
         return (uint64_t)(uint32_t)(s->batch_guestcmd_addr);
     case SYNC_REG_BATCH_GUESTCOMMAND_ADDR_HIGH:
         return (uint64_t)(uint32_t)(s->batch_guestcmd_addr >> 32);
     default:
         DPRINT("INVALID sync_read! reg=%u", offset);
         assert(false);
         return 0;
     }
     return 0;
 }
 // The guest kernel's goldfish_sync driver triggers goldfish_sync_read
 // and goldfish_sync_write. The only purpose of those two functions is to
 // pass the right value to and from the special |regs| field of the
 // goldfish_sync_state.

 static void
 goldfish_sync_write(void *opaque,
                     hwaddr offset,
                     uint64_t val,
                     unsigned size) {

     DPRINT("opaque=%p "
            "offset=0x%lx "
            "sz=0x%x "
            "val=%" PRIu64,
            opaque, offset, size, val);

     struct goldfish_sync_state* s = opaque;

     switch (offset) {
     // SYNC_REG_BATCH_COMMAND write: Used to send acknowledgements
     // to host->guest commands. Some commands that can be issued from
     // the host, such as |goldfish_sync_create_timeline|, require a
     // return value of the timeline pointer itself. Not all commands
     // use this; for example, we never acknowledge any
     // |goldfish_sync_timeline_inc| commands because that would
     // decrease performance.
     case SYNC_REG_BATCH_COMMAND:
         DPRINT("write SYNC_REG_BATCH_COMMAND. obtaining batch cmd vals.");
         struct goldfish_sync_batch_cmd incoming = {
             .cmd = 0,
             .handle = 0,
             .time_arg = 0,
             .hostcmd_handle = 0,
         };
         cpu_physical_memory_read(s->batch_cmd_addr,
                                  (void*)&incoming,
                                  sizeof(struct goldfish_sync_batch_cmd));
         DPRINT("got: cmd=%u handle=0x%llx time_arg=%u hostcmd_handle=0x%llx",
                incoming.cmd,
                incoming.handle,
                incoming.time_arg,
                incoming.hostcmd_handle);
         service_ops->receive_hostcmd_result(
                incoming.cmd,
                incoming.handle,
                incoming.time_arg,
                incoming.hostcmd_handle);
         break;
     // SYNC_REG_BATCH_GUESTCOMMAND write: Used to send
     // guest->host commands. Currently, the only guest->host command
     // that matters is SYNC_GUEST_CMD_TRIGGER_HOST_WAIT, which is used
     // to cause a OpenGL client wait on the host GPU/CPU.
     case SYNC_REG_BATCH_GUESTCOMMAND:
         DPRINT("write SYNC_REG_BATCH_GUESTCOMMAND. obtaining batch cmd vals.");
         struct goldfish_sync_batch_guestcmd guest_incoming = {
             .host_command = 0,
             .glsync_handle = 0,
             .thread_handle = 0,
             .guest_timeline_handle = 0,
         };
         cpu_physical_memory_read(s->batch_guestcmd_addr,
                                  (void*)&guest_incoming,
                                  sizeof(struct goldfish_sync_batch_guestcmd));
         DPRINT("got: cmd=%llu glsync=0x%llx thread=0x%llx timeline=0x%llx",
                 guest_incoming.host_command,
                 guest_incoming.glsync_handle,
                 guest_incoming.thread_handle,
                 guest_incoming.guest_timeline_handle);
         switch (guest_incoming.host_command) {
         case SYNC_GUEST_CMD_TRIGGER_HOST_WAIT:
             DPRINT("exec SYNC_GUEST_CMD_TRIGGER_HOST_WAIT");
             service_ops->trigger_host_wait(guest_incoming.glsync_handle,
                                            guest_incoming.thread_handle,
                                            guest_incoming.guest_timeline_handle);
             break;
         case SYNC_GUEST_CMD_READY:
             DPRINT("exec SYNC_GUEST_CMD_READY");
             break;
         }
         break;
     // SYNC_REG_BATCH_(GUEST)COMMAND_ADDR(_HIGH) write:
     // Used to communicate the physical address on the guest where
     // we write all the info for commands.
     case SYNC_REG_BATCH_COMMAND_ADDR:
         s->batch_cmd_addr = val;
         break;
     case SYNC_REG_BATCH_COMMAND_ADDR_HIGH:
         s->batch_cmd_addr |= (uint64_t)(val << 32);
         DPRINT("Got batch command address. addr=0x%llx",
                s->batch_cmd_addr);
         break;
     case SYNC_REG_BATCH_GUESTCOMMAND_ADDR:
         s->batch_guestcmd_addr = val;
         break;
     case SYNC_REG_BATCH_GUESTCOMMAND_ADDR_HIGH:
         s->batch_guestcmd_addr |= (uint64_t)(val << 32);
         DPRINT("Got batch guestcommand address. addr=0x%llx",
                s->batch_guestcmd_addr);
         break;
     case SYNC_REG_INIT:
         goldfish_sync_reset_device(s);
         break;
     default:
         DPRINT("INVALID sync_write! reg=%u", offset);
         assert(false);
     }
 }

 static const MemoryRegionOps goldfish_sync_iomem_ops = {
     .read = goldfish_sync_read,
     .write = goldfish_sync_write,
     .endianness = DEVICE_NATIVE_ENDIAN,
     .impl.min_access_size = 4,
     .impl.max_access_size = 4
 };

 // goldfish_sync_realize is called on startup if the sync device is enabled.
 // It does the work of setting up the I/O, command queue, and function pointers.
 static void goldfish_sync_realize(DeviceState *dev, Error **errp) {
     DPRINT("enter");
     SysBusDevice* sbdev = SYS_BUS_DEVICE(dev);
     struct goldfish_sync_state* s = GOLDFISH_SYNC(dev);

     s_goldfish_sync_dev = s;

     s->pending = NULL;
     s->current = NULL;

     memory_region_init_io(&s->iomem, OBJECT(s),
                           &goldfish_sync_iomem_ops,
                           s,
                           "goldfish_sync",
                           0x2000);
     sysbus_init_mmio(sbdev, &s->iomem);
     sysbus_init_irq(sbdev, &s->irq);
 }

 static Property goldfish_sync_properties[] = {
     DEFINE_PROP_END_OF_LIST(),
 };

 static void goldfish_sync_class_init(ObjectClass *klass, void *data)
 {
     DPRINT("enter");
     DeviceClass *dc = DEVICE_CLASS(klass);

     dc->realize = goldfish_sync_realize;
     dc->desc = "goldfish sync";
     dc->props = goldfish_sync_properties;
 }

 static const TypeInfo goldfish_sync_info = {
     .name          = TYPE_GOLDFISH_SYNC,
     .parent        = TYPE_SYS_BUS_DEVICE,
     .instance_size = sizeof(struct goldfish_sync_state),
     .class_init    = goldfish_sync_class_init,
 };

 static void goldfish_sync_register(void)
 {
     DPRINT("enter");
     type_register_static(&goldfish_sync_info);
 }

 type_init(goldfish_sync_register);
	/* Copyright (C) 2016 The Android Open Source Project
	**
	** This software is licensed under the terms of the GNU General Public
	** License version 2, as published by the Free Software Foundation, and
	** may be copied, distributed, and modified under those terms.
	**
	** This program is distributed in the hope that it will be useful,
	** but WITHOUT ANY WARRANTY; without even the implied warranty of
	** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	** GNU General Public License for more details.
	*/

	#include "qemu/osdep.h"
	#include "hw/hw.h"
	#include "hw/sysbus.h"
	#include "qemu-common.h"
	#include "qemu/error-report.h"
	#include "qemu/main-loop.h"
	#include "trace.h"
	#include "hw/misc/goldfish_sync.h"

	#include <assert.h>

	// TODO(digit): Plug better logging for Android emulator.
	#define DPRINT(...)

	// Goldfish sync commands=======================================================

	// Batch command formats:
	// Host->guest:
	struct goldfish_sync_batch_cmd {
	// sorted by size for alignment
	uint64_t handle;
	uint64_t hostcmd_handle;
	uint32_t cmd;
	uint32_t time_arg;
	};

	// guest->host:
	struct goldfish_sync_batch_guestcmd {
	uint64_t host_command; // uint64_t for alignment
	uint64_t glsync_handle;
	uint64_t thread_handle;
	uint64_t guest_timeline_handle;
	};

	// This is a suffix of batch cmd.
	// The purpose of the "pending_cmd" variant
	// is so we can queue up several batch commands
	// in the same IRQ level.
	struct goldfish_sync_pending_cmd {
	uint64_t handle;
	uint64_t hostcmd_handle;
	uint32_t cmd;
	uint32_t time_arg;
	struct goldfish_sync_pending_cmd* next;
	};

	// Command numbers that can only be sent from the guest to the device.
	#define SYNC_GUEST_CMD_READY 0
	#define SYNC_GUEST_CMD_TRIGGER_HOST_WAIT 5

	// The register layout is:

	#define SYNC_REG_BATCH_COMMAND 0x00 // host->guest batch commands
	#define SYNC_REG_BATCH_GUESTCOMMAND 0x04 // guest->host batch commands
	#define SYNC_REG_BATCH_COMMAND_ADDR 0x08 // communicate physical address of host->guest batch commands
	#define SYNC_REG_BATCH_COMMAND_ADDR_HIGH 0x0c // 64-bit part
	#define SYNC_REG_BATCH_GUESTCOMMAND_ADDR 0x10 // communicate physical address of guest->host commands
	#define SYNC_REG_BATCH_GUESTCOMMAND_ADDR_HIGH 0x14 // 64-bit part
	#define SYNC_REG_INIT 0x18 // to signal that the device has been detected by the kernel

	// The goldfish sync device is represented by the goldfish_sync_state struct.
	// Besides the machinery necessary to do I/O with the guest:
	// \|pending\|: a linked list of \|goldfish_sync_pending_cmd\|'s
	// that need to be processed by the kernel.
	// \|first_pending_cmd\|: maintains a pointer to the earliest pending command
	// that needs to be sent. We plan to process pending commands in the same
	// order in which they were received.
	// \|current\|: Intermediate value that represents a popped-off pending
	// command.
	// \|batch_cmd_addr\|: Physical memory address where we write the details
	// of each command that comes in from the host. We also read replies
	// from the same address (if applicable)
	// \|batch_guestcmd_addr\|: Physical memory address where we read the
	// details of each command that comes in from the guest.
	// \|ops\|: Callbacks to other areas of the emulator that need to be
	// triggered upon reading a guest->host command.
	struct goldfish_sync_state {
	SysBusDevice parent;
	MemoryRegion iomem;
	qemu_irq irq;

	struct goldfish_sync_pending_cmd* pending;
	struct goldfish_sync_pending_cmd* first_pending_cmd;
	struct goldfish_sync_pending_cmd* current;

	uint64_t batch_cmd_addr;
	uint64_t batch_guestcmd_addr;

	struct goldfish_sync_ops* ops;
	};

	static struct goldfish_sync_state* s_goldfish_sync_dev;

	static const GoldfishSyncServiceOps* service_ops = NULL;

	void goldfish_sync_set_service_ops(const GoldfishSyncServiceOps *ops) {
	service_ops = ops;
	}

	// Command list operations======================================================

	static struct goldfish_sync_pending_cmd*
	goldfish_sync_new_cmd(void) {
	struct goldfish_sync_pending_cmd* res;
	res = g_malloc0(sizeof(struct goldfish_sync_pending_cmd));
	return res;
	}

	static void
	goldfish_sync_free_cmd(struct goldfish_sync_pending_cmd* cmd) {
	g_free(cmd);
	}

	static void
	goldfish_sync_push_cmd(struct goldfish_sync_state* state,
	struct goldfish_sync_pending_cmd* cmd) {

	cmd->next = NULL;

	if (state->pending) {
	state->pending->next = cmd;
	}

	// We need to reset first_pending_cmd if
	// the list was empty to start with.
	if (!state->pending) {
	state->first_pending_cmd = cmd;
	}

	state->pending = cmd;
	}

	static struct goldfish_sync_pending_cmd*
	goldfish_sync_pop_first_cmd(struct goldfish_sync_state* state) {

	struct goldfish_sync_pending_cmd* popped =
	state->first_pending_cmd;

	// Update list structure as follows:
	// 1. Don't do anything if its already empty.
	if (!popped) return NULL;

	// 2. Update first_pending_cmd and pending fields,
	// changing list structure to reflect the change.
	state->first_pending_cmd = popped->next;
	if (state->pending == popped) state->pending = NULL;

	return popped;
	}

	static void goldfish_sync_clear_pending(struct goldfish_sync_state* state) {
	struct goldfish_sync_pending_cmd* curr =
	state->pending;

	while (curr) {
	struct goldfish_sync_pending_cmd* tmp = curr;
	curr = curr->next;
	goldfish_sync_free_cmd(tmp);
	}

	state->pending = NULL;
	state->first_pending_cmd = NULL;
	}

	static void goldfish_sync_reset_device(struct goldfish_sync_state* state) {
	goldfish_sync_clear_pending(state);
	qemu_set_irq(state->irq, 0);
	}

	// Callbacks and hw_funcs struct================================================

	// goldfish_sync_send_command does the actual work of setting up
	// the sync device registers, causing IRQ blip,
	// and waiting for + reading back results from the guest
	// (if appplicable)
	void goldfish_sync_send_command(uint32_t cmd,
	uint64_t handle,
	uint32_t time_arg,
	uint64_t hostcmd_handle) {

	struct goldfish_sync_state* s;
	struct goldfish_sync_pending_cmd* to_send;
	s = s_goldfish_sync_dev;

	DPRINT("incoming cmd. "
	"cmd=%u "
	"handle=0x%llx "
	"time_arg=%u "
	"hostcmd_handle=0x%llx",
	cmd, handle, time_arg, hostcmd_handle);

	to_send = goldfish_sync_new_cmd();
	to_send->cmd = cmd;
	to_send->handle = handle;
	to_send->time_arg = time_arg;
	to_send->hostcmd_handle = hostcmd_handle;

	goldfish_sync_push_cmd(s, to_send);

	qemu_set_irq(s->irq, 1);

	DPRINT("Exit");
	}

	#define TYPE_GOLDFISH_SYNC "goldfish_sync"
	#define GOLDFISH_SYNC(obj) \
	OBJECT_CHECK(struct goldfish_sync_state, (obj), TYPE_GOLDFISH_SYNC)

	static uint64_t
	goldfish_sync_read(void *opaque,
	hwaddr offset,
	unsigned size) {

	DPRINT("opaque=%p offset=0x%lx sz=0x%x", opaque, offset, size);

	struct goldfish_sync_state* s = opaque;
	struct goldfish_sync_batch_cmd* curr_batch_cmd;

	switch (offset) {
	// SYNC_REG_BATCH_COMMAND read:
	// This is triggered by the kernel whenever we are processing
	// any host->guest sync command, such as timeline increment.
	// The role of this part is to pass command info (in the struct
	// \|goldfish_sync_batch_cmd\|'s to the guest where the commands
	// are actually run.
	//
	// SYNC_REG_BATCH_COMMAND is the first thing
	// to happen on a IRQ level raise, and will continue re-issuing
	// throughout IRQ active high, until all pending commands on the
	// host (the linked list) are processed. At that point, IRQ
	// is lowered.
	case SYNC_REG_BATCH_COMMAND:
	s->current = goldfish_sync_pop_first_cmd(s);
	if (!s->current) {
	DPRINT("Out of pending commands. Lower IRQ.");
	struct goldfish_sync_batch_cmd quit_cmd = {
	.cmd = 0, .handle = 0, .time_arg = 0, .hostcmd_handle = 0
	};
	cpu_physical_memory_write(s->batch_cmd_addr,
	(void*)&quit_cmd,
	sizeof(struct goldfish_sync_batch_cmd));
	qemu_set_irq(s->irq, 0);
	return 0;
	} else {
	// goldfish_sync_batch_cmd is a prefix of
	// goldfish_sync_pending_cmd, so we can avoid a copy.
	curr_batch_cmd = (struct goldfish_sync_batch_cmd*)(s->current);
	DPRINT("read SYNC_REG_BATCH_COMMAND. writing to batch addr: "
	"cmd=%u handle=0x%llx time_arg=%u hostcmd_handle=0x%llx",
	curr_batch_cmd->cmd,
	curr_batch_cmd->handle,
	curr_batch_cmd->time_arg,
	curr_batch_cmd->hostcmd_handle);
	cpu_physical_memory_write(s->batch_cmd_addr,
	(void*)curr_batch_cmd,
	sizeof(struct goldfish_sync_batch_cmd));
	goldfish_sync_free_cmd(s->current);
	s->current = NULL;
	}
	DPRINT("done SYNC_REG_BATCH_COMMAND. returning result val?");
	return 0;
	// SYNC_REG_BATCH_(GUEST)COMMAND_ADDR(_HIGH) read:
	// Used solely to verify that the \|s->batch_cmd_addr\| on the host
	// is the same physical address as the corresponding one
	// on the guest.
	case SYNC_REG_BATCH_COMMAND_ADDR:
	return (uint64_t)(uint32_t)(s->batch_cmd_addr);
	case SYNC_REG_BATCH_COMMAND_ADDR_HIGH:
	return (uint64_t)(uint32_t)(s->batch_cmd_addr >> 32);
	case SYNC_REG_BATCH_GUESTCOMMAND_ADDR:
	return (uint64_t)(uint32_t)(s->batch_guestcmd_addr);
	case SYNC_REG_BATCH_GUESTCOMMAND_ADDR_HIGH:
	return (uint64_t)(uint32_t)(s->batch_guestcmd_addr >> 32);
	default:
	DPRINT("INVALID sync_read! reg=%u", offset);
	assert(false);
	return 0;
	}
	return 0;
	}
	// The guest kernel's goldfish_sync driver triggers goldfish_sync_read
	// and goldfish_sync_write. The only purpose of those two functions is to
	// pass the right value to and from the special \|regs\| field of the
	// goldfish_sync_state.

	static void
	goldfish_sync_write(void *opaque,
	hwaddr offset,
	uint64_t val,
	unsigned size) {

	DPRINT("opaque=%p "
	"offset=0x%lx "
	"sz=0x%x "
	"val=%" PRIu64,
	opaque, offset, size, val);

	struct goldfish_sync_state* s = opaque;

	switch (offset) {
	// SYNC_REG_BATCH_COMMAND write: Used to send acknowledgements
	// to host->guest commands. Some commands that can be issued from
	// the host, such as \|goldfish_sync_create_timeline\|, require a
	// return value of the timeline pointer itself. Not all commands
	// use this; for example, we never acknowledge any
	// \|goldfish_sync_timeline_inc\| commands because that would
	// decrease performance.
	case SYNC_REG_BATCH_COMMAND:
	DPRINT("write SYNC_REG_BATCH_COMMAND. obtaining batch cmd vals.");
	struct goldfish_sync_batch_cmd incoming = {
	.cmd = 0,
	.handle = 0,
	.time_arg = 0,
	.hostcmd_handle = 0,
	};
	cpu_physical_memory_read(s->batch_cmd_addr,
	(void*)&incoming,
	sizeof(struct goldfish_sync_batch_cmd));
	DPRINT("got: cmd=%u handle=0x%llx time_arg=%u hostcmd_handle=0x%llx",
	incoming.cmd,
	incoming.handle,
	incoming.time_arg,
	incoming.hostcmd_handle);
	service_ops->receive_hostcmd_result(
	incoming.cmd,
	incoming.handle,
	incoming.time_arg,
	incoming.hostcmd_handle);
	break;
	// SYNC_REG_BATCH_GUESTCOMMAND write: Used to send
	// guest->host commands. Currently, the only guest->host command
	// that matters is SYNC_GUEST_CMD_TRIGGER_HOST_WAIT, which is used
	// to cause a OpenGL client wait on the host GPU/CPU.
	case SYNC_REG_BATCH_GUESTCOMMAND:
	DPRINT("write SYNC_REG_BATCH_GUESTCOMMAND. obtaining batch cmd vals.");
	struct goldfish_sync_batch_guestcmd guest_incoming = {
	.host_command = 0,
	.glsync_handle = 0,
	.thread_handle = 0,
	.guest_timeline_handle = 0,
	};
	cpu_physical_memory_read(s->batch_guestcmd_addr,
	(void*)&guest_incoming,
	sizeof(struct goldfish_sync_batch_guestcmd));
	DPRINT("got: cmd=%llu glsync=0x%llx thread=0x%llx timeline=0x%llx",
	guest_incoming.host_command,
	guest_incoming.glsync_handle,
	guest_incoming.thread_handle,
	guest_incoming.guest_timeline_handle);
	switch (guest_incoming.host_command) {
	case SYNC_GUEST_CMD_TRIGGER_HOST_WAIT:
	DPRINT("exec SYNC_GUEST_CMD_TRIGGER_HOST_WAIT");
	service_ops->trigger_host_wait(guest_incoming.glsync_handle,
	guest_incoming.thread_handle,
	guest_incoming.guest_timeline_handle);
	break;
	case SYNC_GUEST_CMD_READY:
	DPRINT("exec SYNC_GUEST_CMD_READY");
	break;
	}
	break;
	// SYNC_REG_BATCH_(GUEST)COMMAND_ADDR(_HIGH) write:
	// Used to communicate the physical address on the guest where
	// we write all the info for commands.
	case SYNC_REG_BATCH_COMMAND_ADDR:
	s->batch_cmd_addr = val;
	break;
	case SYNC_REG_BATCH_COMMAND_ADDR_HIGH:
	s->batch_cmd_addr \|= (uint64_t)(val << 32);
	DPRINT("Got batch command address. addr=0x%llx",
	s->batch_cmd_addr);
	break;
	case SYNC_REG_BATCH_GUESTCOMMAND_ADDR:
	s->batch_guestcmd_addr = val;
	break;
	case SYNC_REG_BATCH_GUESTCOMMAND_ADDR_HIGH:
	s->batch_guestcmd_addr \|= (uint64_t)(val << 32);
	DPRINT("Got batch guestcommand address. addr=0x%llx",
	s->batch_guestcmd_addr);
	break;
	case SYNC_REG_INIT:
	goldfish_sync_reset_device(s);
	break;
	default:
	DPRINT("INVALID sync_write! reg=%u", offset);
	assert(false);
	}
	}

	static const MemoryRegionOps goldfish_sync_iomem_ops = {
	.read = goldfish_sync_read,
	.write = goldfish_sync_write,
	.endianness = DEVICE_NATIVE_ENDIAN,
	.impl.min_access_size = 4,
	.impl.max_access_size = 4
	};

	// goldfish_sync_realize is called on startup if the sync device is enabled.
	// It does the work of setting up the I/O, command queue, and function pointers.
	static void goldfish_sync_realize(DeviceState dev, Error *errp) {
	DPRINT("enter");
	SysBusDevice* sbdev = SYS_BUS_DEVICE(dev);
	struct goldfish_sync_state* s = GOLDFISH_SYNC(dev);

	s_goldfish_sync_dev = s;

	s->pending = NULL;
	s->current = NULL;

	memory_region_init_io(&s->iomem, OBJECT(s),
	&goldfish_sync_iomem_ops,
	s,
	"goldfish_sync",
	0x2000);
	sysbus_init_mmio(sbdev, &s->iomem);
	sysbus_init_irq(sbdev, &s->irq);
	}

	static Property goldfish_sync_properties[] = {
	DEFINE_PROP_END_OF_LIST(),
	};

	static void goldfish_sync_class_init(ObjectClass klass, void data)
	{
	DPRINT("enter");
	DeviceClass *dc = DEVICE_CLASS(klass);

	dc->realize = goldfish_sync_realize;
	dc->desc = "goldfish sync";
	dc->props = goldfish_sync_properties;
	}

	static const TypeInfo goldfish_sync_info = {
	.name = TYPE_GOLDFISH_SYNC,
	.parent = TYPE_SYS_BUS_DEVICE,
	.instance_size = sizeof(struct goldfish_sync_state),
	.class_init = goldfish_sync_class_init,
	};

	static void goldfish_sync_register(void)
	{
	DPRINT("enter");
	type_register_static(&goldfish_sync_info);
	}

	type_init(goldfish_sync_register);