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drm/nouveau/i2c: handle bit-banging ourselves
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i2c-algo-bit doesn't actually work very well on one card I have access to
(NVS 300), random single-bit errors occur most of the time - what we're
doing now is closer to what xf86i2c.c does.

The original plan was to figure out why i2c-algo-bit fails on the NVS 300,
and fix it.  However, while investigating I discovered i2c-algo-bit calls
cond_resched(), which makes it a bad idea for us to be using as we execute
VBIOS scripts from a tasklet, and there may very well be i2c transfers as
a result.

So, since I already wrote this code in userspace to track down the NVS 300
bug, and it's not really much code - lets use it.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
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Ben Skeggs committed Dec 21, 2011
1 parent 9e3b6b9 commit f553b79
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Showing 2 changed files with 178 additions and 22 deletions.
199 changes: 178 additions & 21 deletions drivers/gpu/drm/nouveau/nouveau_i2c.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,10 @@
#include "nouveau_i2c.h"
#include "nouveau_hw.h"

#define T_TIMEOUT 2200000
#define T_RISEFALL 1000
#define T_HOLD 5000

static void
i2c_drive_scl(void *data, int state)
{
Expand Down Expand Up @@ -109,6 +113,175 @@ i2c_sense_sda(void *data)
return 0;
}

static void
i2c_delay(struct nouveau_i2c_chan *port, u32 nsec)
{
udelay((nsec + 500) / 1000);
}

static bool
i2c_raise_scl(struct nouveau_i2c_chan *port)
{
u32 timeout = T_TIMEOUT / T_RISEFALL;

i2c_drive_scl(port, 1);
do {
i2c_delay(port, T_RISEFALL);
} while (!i2c_sense_scl(port) && --timeout);

return timeout != 0;
}

static int
i2c_start(struct nouveau_i2c_chan *port)
{
int ret = 0;

port->state = i2c_sense_scl(port);
port->state |= i2c_sense_sda(port) << 1;
if (port->state != 3) {
i2c_drive_scl(port, 0);
i2c_drive_sda(port, 1);
if (!i2c_raise_scl(port))
ret = -EBUSY;
}

i2c_drive_sda(port, 0);
i2c_delay(port, T_HOLD);
i2c_drive_scl(port, 0);
i2c_delay(port, T_HOLD);
return ret;
}

static void
i2c_stop(struct nouveau_i2c_chan *port)
{
i2c_drive_scl(port, 0);
i2c_drive_sda(port, 0);
i2c_delay(port, T_RISEFALL);

i2c_drive_scl(port, 1);
i2c_delay(port, T_HOLD);
i2c_drive_sda(port, 1);
i2c_delay(port, T_HOLD);
}

static int
i2c_bitw(struct nouveau_i2c_chan *port, int sda)
{
i2c_drive_sda(port, sda);
i2c_delay(port, T_RISEFALL);

if (!i2c_raise_scl(port))
return -ETIMEDOUT;
i2c_delay(port, T_HOLD);

i2c_drive_scl(port, 0);
i2c_delay(port, T_HOLD);
return 0;
}

static int
i2c_bitr(struct nouveau_i2c_chan *port)
{
int sda;

i2c_drive_sda(port, 1);
i2c_delay(port, T_RISEFALL);

if (!i2c_raise_scl(port))
return -ETIMEDOUT;
i2c_delay(port, T_HOLD);

sda = i2c_sense_sda(port);

i2c_drive_scl(port, 0);
i2c_delay(port, T_HOLD);
return sda;
}

static int
i2c_get_byte(struct nouveau_i2c_chan *port, u8 *byte, bool last)
{
int i, bit;

*byte = 0;
for (i = 7; i >= 0; i--) {
bit = i2c_bitr(port);
if (bit < 0)
return bit;
*byte |= bit << i;
}

return i2c_bitw(port, last ? 1 : 0);
}

static int
i2c_put_byte(struct nouveau_i2c_chan *port, u8 byte)
{
int i, ret;
for (i = 7; i >= 0; i--) {
ret = i2c_bitw(port, !!(byte & (1 << i)));
if (ret < 0)
return ret;
}

ret = i2c_bitr(port);
if (ret == 1) /* nack */
ret = -EIO;
return ret;
}

static int
i2c_addr(struct nouveau_i2c_chan *port, struct i2c_msg *msg)
{
u32 addr = msg->addr << 1;
if (msg->flags & I2C_M_RD)
addr |= 1;
return i2c_put_byte(port, addr);
}

static int
i2c_bit_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
struct nouveau_i2c_chan *port = (struct nouveau_i2c_chan *)adap;
struct i2c_msg *msg = msgs;
int ret = 0, mcnt = num;

while (!ret && mcnt--) {
u8 remaining = msg->len;
u8 *ptr = msg->buf;

ret = i2c_start(port);
if (ret == 0)
ret = i2c_addr(port, msg);

if (msg->flags & I2C_M_RD) {
while (!ret && remaining--)
ret = i2c_get_byte(port, ptr++, !remaining);
} else {
while (!ret && remaining--)
ret = i2c_put_byte(port, *ptr++);
}

msg++;
}

i2c_stop(port);
return (ret < 0) ? ret : num;
}

static u32
i2c_bit_func(struct i2c_adapter *adap)
{
return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
}

const struct i2c_algorithm i2c_bit_algo = {
.master_xfer = i2c_bit_xfer,
.functionality = i2c_bit_func
};

static const uint32_t nv50_i2c_port[] = {
0x00e138, 0x00e150, 0x00e168, 0x00e180,
0x00e254, 0x00e274, 0x00e764, 0x00e780,
Expand Down Expand Up @@ -211,10 +384,12 @@ nouveau_i2c_init(struct drm_device *dev)
case 0: /* NV04:NV50 */
port->drive = entry[0];
port->sense = entry[1];
port->adapter.algo = &i2c_bit_algo;
break;
case 4: /* NV4E */
port->drive = 0x600800 + entry[1];
port->sense = port->drive;
port->adapter.algo = &i2c_bit_algo;
break;
case 5: /* NV50- */
port->drive = entry[0] & 0x0f;
Expand All @@ -227,6 +402,7 @@ nouveau_i2c_init(struct drm_device *dev)
port->drive = 0x00d014 + (port->drive * 0x20);
port->sense = port->drive;
}
port->adapter.algo = &i2c_bit_algo;
break;
case 6: /* NV50- DP AUX */
port->drive = entry[0];
Expand All @@ -237,7 +413,7 @@ nouveau_i2c_init(struct drm_device *dev)
break;
}

if (!port->adapter.algo && !port->drive) {
if (!port->adapter.algo) {
NV_ERROR(dev, "I2C%d: type %d index %x/%x unknown\n",
i, port->type, port->drive, port->sense);
kfree(port);
Expand All @@ -253,26 +429,7 @@ nouveau_i2c_init(struct drm_device *dev)
port->dcb = ROM32(entry[0]);
i2c_set_adapdata(&port->adapter, i2c);

if (port->adapter.algo != &nouveau_dp_i2c_algo) {
port->adapter.algo_data = &port->bit;
port->bit.udelay = 40;
port->bit.timeout = usecs_to_jiffies(5000);
port->bit.data = port;
port->bit.setsda = i2c_drive_sda;
port->bit.setscl = i2c_drive_scl;
port->bit.getsda = i2c_sense_sda;
port->bit.getscl = i2c_sense_scl;

i2c_drive_scl(port, 0);
i2c_drive_sda(port, 1);
i2c_drive_scl(port, 1);

ret = i2c_bit_add_bus(&port->adapter);
} else {
port->adapter.algo = &nouveau_dp_i2c_algo;
ret = i2c_add_adapter(&port->adapter);
}

ret = i2c_add_adapter(&port->adapter);
if (ret) {
NV_ERROR(dev, "I2C%d: failed register: %d\n", i, ret);
kfree(port);
Expand Down
1 change: 0 additions & 1 deletion drivers/gpu/drm/nouveau/nouveau_i2c.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -34,7 +34,6 @@
struct nouveau_i2c_chan {
struct i2c_adapter adapter;
struct drm_device *dev;
struct i2c_algo_bit_data bit;
struct list_head head;
u8 index;
u8 type;
Expand Down

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