Re: [PATCH] drm/i915: Fix single msg gmbus_xfers writes

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Feb 09, 2012 at 12:03:17PM -0800, Benson Leung wrote:
> gmbus_xfer with a single message (particularly a single message write) would
> set Bus Cycle Select to 100b, the Gen Stop cycle, instead of 101b,
> No Index, Stop cycle. This would not start single message i2c transactions.
> 
> Also, gmbus_xfer done: will disable the interface without checking if
> it is idle. In the case of writes, there will be no wait on status or delay
> to ensure the write starts and completes before the interface is turned off.
> 
> Fixed the former issue by using the same cycle selection as used in the
> I2C_M_RD for the write case.
> GMBUS_CYCLE_WAIT | (i + 1 == num ? GMBUS_CYCLE_STOP : 0)
> Fixed the latter by waiting on GMBUS_ACTIVE to deassert before disable.
> 
> Signed-off-by: Benson Leung <bleung@chromium.org>
> ---
>  drivers/gpu/drm/i915/intel_i2c.c |   13 +++++++++----
>  1 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
> index d30cccc..64bb9cd 100644
> --- a/drivers/gpu/drm/i915/intel_i2c.c
> +++ b/drivers/gpu/drm/i915/intel_i2c.c
> @@ -249,7 +249,8 @@ gmbus_xfer(struct i2c_adapter *adapter,
>  
>  		if (msgs[i].flags & I2C_M_RD) {
>  			I915_WRITE(GMBUS1 + reg_offset,
> -				   GMBUS_CYCLE_WAIT | (i + 1 == num ? GMBUS_CYCLE_STOP : 0) |
> +				   GMBUS_CYCLE_WAIT |
> +				   (i + 1 == num ? GMBUS_CYCLE_STOP : 0) |
>  				   (len << GMBUS_BYTE_COUNT_SHIFT) |
>  				   (msgs[i].addr << GMBUS_SLAVE_ADDR_SHIFT) |
>  				   GMBUS_SLAVE_READ | GMBUS_SW_RDY);

This here looks like just a white-space change. But your commit message
sounds like it's not jsut write's that are affected by this issue and need
to be fixed. Can you please clear up this for easily confused me?

Thanks, Daniel

> @@ -278,7 +279,8 @@ gmbus_xfer(struct i2c_adapter *adapter,
>  
>  			I915_WRITE(GMBUS3 + reg_offset, val);
>  			I915_WRITE(GMBUS1 + reg_offset,
> -				   (i + 1 == num ? GMBUS_CYCLE_STOP : GMBUS_CYCLE_WAIT) |
> +				   GMBUS_CYCLE_WAIT |
> +				   (i + 1 == num ? GMBUS_CYCLE_STOP : 0) |
>  				   (msgs[i].len << GMBUS_BYTE_COUNT_SHIFT) |
>  				   (msgs[i].addr << GMBUS_SLAVE_ADDR_SHIFT) |
>  				   GMBUS_SLAVE_WRITE | GMBUS_SW_RDY);
> @@ -317,9 +319,12 @@ clear_err:
>  	I915_WRITE(GMBUS1 + reg_offset, 0);
>  
>  done:
> -	/* Mark the GMBUS interface as disabled. We will re-enable it at the
> -	 * start of the next xfer, till then let it sleep.
> +	/* 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))
> +		DRM_INFO("GMBUS timed out waiting for idle\n");
>  	I915_WRITE(GMBUS0 + reg_offset, 0);
>  	return i;
>  
> -- 
> 1.7.1
> 
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-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48