[PATCH 4/8 v7] drm/i915/intel_i2c: use WAIT cycle, not STOP

Daniel Kurtz
2012-03-30T11:47:55Z

The i915 is only able to generate a STOP cycle (i.e. finalize an i2c
transaction) during a DATA or WAIT phase. In other words, the
controller rejects a STOP requested as part of the first transaction in a
sequence.

Thus, for the first transaction we must always use a WAIT cycle, detect
when the device has finished (and is in a WAIT phase), and then either
start the next transaction, or, if there are no more transactions,
generate a STOP cycle.

Note: Theoretically, the last transaction of a multi-transaction sequence
could initiate a STOP cycle. However, this slight optimization is left
for another patch. We return -ETIMEDOUT if the hardware doesn't
deactivate after the STOP cycle.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
---
drivers/gpu/drm/i915/intel_i2c.c | 30 +++++++++++++++---------------
1 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
index 9707868..25f2c9e 100644
--- a/drivers/gpu/drm/i915/intel_i2c.c
+++ b/drivers/gpu/drm/i915/intel_i2c.c
@@ -204,8 +204,7 @@ intel_gpio_setup(struct intel_gmbus *bus, u32 pin)
}

static int
-gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
- bool last)
+gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
{
int reg_offset = dev_priv->gpio_mmio_base;
u16 len = msg->len;
@@ -213,7 +212,6 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,

I915_WRITE(GMBUS1 + reg_offset,
GMBUS_CYCLE_WAIT |
- (last ? GMBUS_CYCLE_STOP : 0) |
(len << GMBUS_BYTE_COUNT_SHIFT) |
(msg->addr << GMBUS_SLAVE_ADDR_SHIFT) |
GMBUS_SLAVE_READ | GMBUS_SW_RDY);
@@ -239,8 +237,7 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
}

static int
-gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
- bool last)
+gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
{
int reg_offset = dev_priv->gpio_mmio_base;
u16 len = msg->len;
@@ -256,7 +253,6 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
I915_WRITE(GMBUS3 + reg_offset, val);
I915_WRITE(GMBUS1 + reg_offset,
GMBUS_CYCLE_WAIT |
- (last ? GMBUS_CYCLE_STOP : 0) |
(msg->len << GMBUS_BYTE_COUNT_SHIFT) |
(msg->addr << GMBUS_SLAVE_ADDR_SHIFT) |
GMBUS_SLAVE_WRITE | GMBUS_SW_RDY);
@@ -289,7 +285,8 @@ gmbus_xfer(struct i2c_adapter *adapter,
struct intel_gmbus,
adapter);
struct drm_i915_private *dev_priv = bus->dev_priv;
- int i, reg_offset, ret;
+ int i, reg_offset;
+ int ret = 0;

mutex_lock(&dev_priv->gmbus_mutex);

@@ -303,20 +300,17 @@ gmbus_xfer(struct i2c_adapter *adapter,
I915_WRITE(GMBUS0 + reg_offset, bus->reg0);

for (i = 0; i < num; i++) {
- bool last = i + 1 == num;
-
if (msgs[i].flags & I2C_M_RD)
- ret = gmbus_xfer_read(dev_priv, &msgs[i], last);
+ ret = gmbus_xfer_read(dev_priv, &msgs[i]);
else
- ret = gmbus_xfer_write(dev_priv, &msgs[i], last);
+ ret = gmbus_xfer_write(dev_priv, &msgs[i]);

if (ret == -ETIMEDOUT)
goto timeout;
if (ret == -ENXIO)
goto clear_err;

- if (!last &&
- wait_for(I915_READ(GMBUS2 + reg_offset) &
+ if (wait_for(I915_READ(GMBUS2 + reg_offset) &
(GMBUS_SATOER | GMBUS_HW_WAIT_PHASE),
50))
goto timeout;
@@ -324,15 +318,21 @@ gmbus_xfer(struct i2c_adapter *adapter,
goto clear_err;
}

+ /* Generate a STOP condition on the bus */
+ I915_WRITE(GMBUS1 + reg_offset, GMBUS_CYCLE_STOP | GMBUS_SW_RDY);
+
/* Mark the GMBUS interface as disabled after waiting for idle.
* We will re-enable it at the start of the next xfer,
* till then let it sleep.
*/
- if (wait_for((I915_READ(GMBUS2 + reg_offset) & GMBUS_ACTIVE) == 0, 10))
+ if (wait_for((I915_READ(GMBUS2 + reg_offset) & GMBUS_ACTIVE) == 0,
+ 10)) {
DRM_INFO("GMBUS [%s] timed out waiting for idle\n",
adapter->name);
+ ret = -ETIMEDOUT;
+ }
I915_WRITE(GMBUS0 + reg_offset, 0);
- ret = i;
+ ret = ret ?: i;
goto out;

clear_err:
--
1.7.7.3