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

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Mar 30, 2012 at 07:46:39PM +0800, Daniel Kurtz wrote:
> 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>

I've re-read gmbus register spec and STOP seems to be allowed even in the
first cycle. Does this patch solve an issue for you? If not, I prefer we
just drop it.
-Daniel

> ---
>  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
> 

-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48