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qemu/hw/i2c/bitbang_i2c.c
Peter Maydell 9706e0162d hw/i2c/bitbang_i2c: Handle NACKs from devices 
If the guest attempts to talk to a nonexistent device over i2c,
the i2c_start_transfer() function will return non-zero, indicating
that the bus is signalling a NACK. Similarly, if the i2c_send()
function returns nonzero then the target device returned a NACK.
Handle this possibility in the bitbang_i2c code, by returning
the state machine to the STOPPED state and returning the NACK
bit to the guest.

This bit of missing functionality was spotted by Coverity
(it noticed that we weren't checking the return value from
i2c_start_transfer()).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1477332749-27098-1-git-send-email-peter.maydell@linaro.org
2016-11-07 10:01:15 +00:00

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/*
* Bit-Bang i2c emulation extracted from
* Marvell MV88W8618 / Freecom MusicPal emulation.
*
* Copyright (c) 2008 Jan Kiszka
*
* This code is licensed under the GNU GPL v2.
*
* Contributions after 2012-01-13 are licensed under the terms of the
* GNU GPL, version 2 or (at your option) any later version.
*/
#include "qemu/osdep.h"
#include "hw/hw.h"
#include "bitbang_i2c.h"
#include "hw/sysbus.h"
//#define DEBUG_BITBANG_I2C
#ifdef DEBUG_BITBANG_I2C
#define DPRINTF(fmt, ...) \
do { printf("bitbang_i2c: " fmt , ## __VA_ARGS__); } while (0)
#else
#define DPRINTF(fmt, ...) do {} while(0)
#endif
typedef enum bitbang_i2c_state {
STOPPED = 0,
SENDING_BIT7,
SENDING_BIT6,
SENDING_BIT5,
SENDING_BIT4,
SENDING_BIT3,
SENDING_BIT2,
SENDING_BIT1,
SENDING_BIT0,
WAITING_FOR_ACK,
RECEIVING_BIT7,
RECEIVING_BIT6,
RECEIVING_BIT5,
RECEIVING_BIT4,
RECEIVING_BIT3,
RECEIVING_BIT2,
RECEIVING_BIT1,
RECEIVING_BIT0,
SENDING_ACK,
SENT_NACK
} bitbang_i2c_state;
struct bitbang_i2c_interface {
I2CBus *bus;
bitbang_i2c_state state;
int last_data;
int last_clock;
int device_out;
uint8_t buffer;
int current_addr;
};
static void bitbang_i2c_enter_stop(bitbang_i2c_interface *i2c)
{
DPRINTF("STOP\n");
if (i2c->current_addr >= 0)
i2c_end_transfer(i2c->bus);
i2c->current_addr = -1;
i2c->state = STOPPED;
}
/* Set device data pin. */
static int bitbang_i2c_ret(bitbang_i2c_interface *i2c, int level)
{
i2c->device_out = level;
//DPRINTF("%d %d %d\n", i2c->last_clock, i2c->last_data, i2c->device_out);
return level & i2c->last_data;
}
/* Leave device data pin unodified. */
static int bitbang_i2c_nop(bitbang_i2c_interface *i2c)
{
return bitbang_i2c_ret(i2c, i2c->device_out);
}
/* Returns data line level. */
int bitbang_i2c_set(bitbang_i2c_interface *i2c, int line, int level)
{
int data;
if (level != 0 && level != 1) {
abort();
}
if (line == BITBANG_I2C_SDA) {
if (level == i2c->last_data) {
return bitbang_i2c_nop(i2c);
}
i2c->last_data = level;
if (i2c->last_clock == 0) {
return bitbang_i2c_nop(i2c);
}
if (level == 0) {
DPRINTF("START\n");
/* START condition. */
i2c->state = SENDING_BIT7;
i2c->current_addr = -1;
} else {
/* STOP condition. */
bitbang_i2c_enter_stop(i2c);
}
return bitbang_i2c_ret(i2c, 1);
}
data = i2c->last_data;
if (i2c->last_clock == level) {
return bitbang_i2c_nop(i2c);
}
i2c->last_clock = level;
if (level == 0) {
/* State is set/read at the start of the clock pulse.
release the data line at the end. */
return bitbang_i2c_ret(i2c, 1);
}
switch (i2c->state) {
case STOPPED:
case SENT_NACK:
return bitbang_i2c_ret(i2c, 1);
case SENDING_BIT7 ... SENDING_BIT0:
i2c->buffer = (i2c->buffer << 1) | data;
/* will end up in WAITING_FOR_ACK */
i2c->state++;
return bitbang_i2c_ret(i2c, 1);
case WAITING_FOR_ACK:
{
int ret;
if (i2c->current_addr < 0) {
i2c->current_addr = i2c->buffer;
DPRINTF("Address 0x%02x\n", i2c->current_addr);
ret = i2c_start_transfer(i2c->bus, i2c->current_addr >> 1,
i2c->current_addr & 1);
} else {
DPRINTF("Sent 0x%02x\n", i2c->buffer);
ret = i2c_send(i2c->bus, i2c->buffer);
}
if (ret) {
/* NACK (either addressing a nonexistent device, or the
* device we were sending to decided to NACK us).
*/
DPRINTF("Got NACK\n");
bitbang_i2c_enter_stop(i2c);
return bitbang_i2c_ret(i2c, 1);
}
if (i2c->current_addr & 1) {
i2c->state = RECEIVING_BIT7;
} else {
i2c->state = SENDING_BIT7;
}
return bitbang_i2c_ret(i2c, 0);
}
case RECEIVING_BIT7:
i2c->buffer = i2c_recv(i2c->bus);
DPRINTF("RX byte 0x%02x\n", i2c->buffer);
/* Fall through... */
case RECEIVING_BIT6 ... RECEIVING_BIT0:
data = i2c->buffer >> 7;
/* will end up in SENDING_ACK */
i2c->state++;
i2c->buffer <<= 1;
return bitbang_i2c_ret(i2c, data);
case SENDING_ACK:
i2c->state = RECEIVING_BIT7;
if (data != 0) {
DPRINTF("NACKED\n");
i2c->state = SENT_NACK;
i2c_nack(i2c->bus);
} else {
DPRINTF("ACKED\n");
}
return bitbang_i2c_ret(i2c, 1);
}
abort();
}
bitbang_i2c_interface *bitbang_i2c_init(I2CBus *bus)
{
bitbang_i2c_interface *s;
s = g_malloc0(sizeof(bitbang_i2c_interface));
s->bus = bus;
s->last_data = 1;
s->last_clock = 1;
s->device_out = 1;
return s;
}
/* GPIO interface. */
#define TYPE_GPIO_I2C "gpio_i2c"
#define GPIO_I2C(obj) OBJECT_CHECK(GPIOI2CState, (obj), TYPE_GPIO_I2C)
typedef struct GPIOI2CState {
SysBusDevice parent_obj;
MemoryRegion dummy_iomem;
bitbang_i2c_interface *bitbang;
int last_level;
qemu_irq out;
} GPIOI2CState;
static void bitbang_i2c_gpio_set(void *opaque, int irq, int level)
{
GPIOI2CState *s = opaque;
level = bitbang_i2c_set(s->bitbang, irq, level);
if (level != s->last_level) {
s->last_level = level;
qemu_set_irq(s->out, level);
}
}
static void gpio_i2c_init(Object *obj)
{
DeviceState *dev = DEVICE(obj);
GPIOI2CState *s = GPIO_I2C(obj);
SysBusDevice *sbd = SYS_BUS_DEVICE(obj);
I2CBus *bus;
memory_region_init(&s->dummy_iomem, obj, "gpio_i2c", 0);
sysbus_init_mmio(sbd, &s->dummy_iomem);
bus = i2c_init_bus(dev, "i2c");
s->bitbang = bitbang_i2c_init(bus);
qdev_init_gpio_in(dev, bitbang_i2c_gpio_set, 2);
qdev_init_gpio_out(dev, &s->out, 1);
}
static void gpio_i2c_class_init(ObjectClass *klass, void *data)
{
DeviceClass *dc = DEVICE_CLASS(klass);
set_bit(DEVICE_CATEGORY_BRIDGE, dc->categories);
dc->desc = "Virtual GPIO to I2C bridge";
}
static const TypeInfo gpio_i2c_info = {
.name = TYPE_GPIO_I2C,
.parent = TYPE_SYS_BUS_DEVICE,
.instance_size = sizeof(GPIOI2CState),
.instance_init = gpio_i2c_init,
.class_init = gpio_i2c_class_init,
};
static void bitbang_i2c_register_types(void)
{
type_register_static(&gpio_i2c_info);
}
type_init(bitbang_i2c_register_types)
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