drm/nouveau/i2c: handle bit-banging ourselves

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>

1 files changed, 178 insertions, 21 deletions

diff --git a/drivers/gpu/drm/nouveau/nouveau_i2c.c b/drivers/gpu/drm/nouveau/nouveau_i2c.c
index 116ef3193fc7..820ae7f52044 100644
--- a/drivers/gpu/drm/nouveau/nouveau_i2c.c
+++ b/drivers/gpu/drm/nouveau/nouveau_i2c.c
@@ -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)
 {
@@ -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,
@@ -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;
@@ -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];
@@ -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);
@@ -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);