Re: [PATCH 2/3] drm/i915/: Initialise trans_min for skl_compute_transition_wm()

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Wed, Nov 15, 2017 at 10:50:35AM +0000, Chris Wilson wrote:
> clang spots
> 
> drivers/gpu/drm/i915/intel_pm.c:4655:6: warning: variable 'trans_min' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
>         if (INTEL_GEN(dev_priv) >= 10)
> 
> but fortunately for us we skip the function unless on a gen10+ device.
> However, to keep the function generic in case we do want to re-enable it
> for gen9 again, initialise trans_min to 0.

Based on this comment:  /* Transition WM are not recommended by HW team for GEN9 */

I believe the function should be called cnl_compute_transition_wm

plus:

-  uint16_t trans_min, trans_y_tile_min;
+  u16 trans_min = 4, trans_y_tile_min;

-  if (INTEL_GEN(dev_priv) >= 10)
-  	trans_min = 4;

Also Wa for CNL A0 can be removed... We never put our hands in on A0...

But in case you want to go with the quick fix:
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

up to you.

> 
> References: ca47667f523e ("drm/i915/gen10: Calculate and enable transition WM")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Mahesh Kumar <mahesh1.kumar@intel.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Jani Nikula <jani.nikula@linux.intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 8c69ec9eb6ee..5d8babfaec30 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4649,6 +4649,7 @@ static void skl_compute_transition_wm(struct intel_crtc_state *cstate,
>  	if (!dev_priv->ipc_enabled)
>  		goto exit;
>  
> +	trans_min = 0;
>  	if (INTEL_GEN(dev_priv) >= 10)
>  		trans_min = 4;
>  
> -- 
> 2.15.0
> 
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