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Commit 72d66afd authored by Daniel Kurtz's avatar Daniel Kurtz Committed by Daniel Vetter
Browse files

drm/i915/intel_i2c: use WAIT cycle, not STOP 



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: default avatarDaniel Kurtz <djkurtz@chromium.org>
[danvet: added comment to the code that gmbus can't generate STOP on
the very first cycle.]
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
parent e646d577

drivers/gpu/drm/i915/intel_i2c.c

+18 −15
Original line number Diff line number Diff line
@@ -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 +318,24 @@ gmbus_xfer(struct i2c_adapter *adapter, 
			goto clear_err;

	}



	/* Generate a STOP condition on the bus. Note that gmbus can't generata

	 * a STOP on the very first cycle. To simplify the code we

	 * unconditionally generate the STOP condition with an additional gmbus

	 * cycle. */

	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: