[Intel-gfx] [PATCH] drm/i915: GMBUS don't need no forcewake

[Chris Wilson]

On Wed, Oct 12, 2016 at 02:44:47PM +0300, ville.syrjala at linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> GMBUS is part of the display engine, and thus has no need for
> forcewake. Let's not bother trying to grab it then.
> 
> I don't recall if the display engine suffers from system hangs
> due to multiple accesses to the same "cacheline" in mmio space.
> I hope not since we're no longer protected by the uncore lock
> since commit 4e6c2d58ba86 ("drm/i915: Take forcewake once for
> the entire GMBUS transaction")

Only applies to concurrent access to the same cacheline, in this case
should be serialised by the mutex around the gmbus xfer.
 
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: David Weinehall <david.weinehall at linux.intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_i2c.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
> index 79aab9ad6faa..49c7824a4c29 100644
> --- a/drivers/gpu/drm/i915/intel_i2c.c
> +++ b/drivers/gpu/drm/i915/intel_i2c.c
> @@ -468,13 +468,9 @@ do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
>  					       struct intel_gmbus,
>  					       adapter);
>  	struct drm_i915_private *dev_priv = bus->dev_priv;
> -	const unsigned int fw =
> -		intel_uncore_forcewake_for_reg(dev_priv, GMBUS0,
> -					       FW_REG_READ | FW_REG_WRITE);
>  	int i = 0, inc, try = 0;
>  	int ret = 0;

I915_WARN_ON(intel_uncore_forcewake_for_reg(dev_priv, GMBUS0,
					    FW_REG_READ |
					    FW_REG_WRITE));

? Would be good to test the fw handling as well.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre