[Intel-gfx] [PATCH] drm/i915: Avoid clearing the base drm_crtc_state

[Chris Wilson]

On Mon, Mar 06, 2017 at 06:46:16PM +0100, Daniel Vetter wrote:
> On Fri, Mar 03, 2017 at 03:46:44PM +0000, Chris Wilson wrote:
> > To prevent having to preserve the drm_crtc_state as we clear the
> > intel_crtc_state, only memset our extended state.
> > 
> > Fixes:
> > drivers/gpu/drm/i915/intel_display.c: In function ‘clear_intel_crtc_state’:
> > drivers/gpu/drm/i915/intel_display.c:11301:1: error: the frame size of 1056 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> >  drivers/gpu/drm/i915/intel_display.c | 6 ++----
> >  1 file changed, 2 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index e6881a69a88f..cfab4d135af3 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -11269,7 +11269,6 @@ clear_intel_crtc_state(struct intel_crtc_state *crtc_state)
> >  {
> >  	struct drm_i915_private *dev_priv =
> >  		to_i915(crtc_state->base.crtc->dev);
> > -	struct drm_crtc_state tmp_state;
> >  	struct intel_crtc_scaler_state scaler_state;
> >  	struct intel_dpll_hw_state dpll_hw_state;
> >  	struct intel_shared_dpll *shared_dpll;
> > @@ -11281,7 +11280,6 @@ clear_intel_crtc_state(struct intel_crtc_state *crtc_state)
> >  	 * fixed, so that the crtc_state can be safely duplicated. For now,
> >  	 * only fields that are know to not cause problems are preserved. */
> >  
> > -	tmp_state = crtc_state->base;
> >  	scaler_state = crtc_state->scaler_state;
> >  	shared_dpll = crtc_state->shared_dpll;
> >  	dpll_hw_state = crtc_state->dpll_hw_state;
> > @@ -11289,9 +11287,9 @@ clear_intel_crtc_state(struct intel_crtc_state *crtc_state)
> >  	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
> >  		wm_state = crtc_state->wm;
> >  
> > -	memset(crtc_state, 0, sizeof *crtc_state);
> > +	memset(&crtc_state->base + 1, 0,
> > +	       sizeof(*crtc_state) - sizeof(crtc_state->base));
> 
> Maybe add a comment like /* Only clear our part of the overall struct. */
> or similar, since this is not entirely obvious what's going on. Also
> 
> 	COMPILE_BUG_ON(offsetof(struct intel_crtc_state, base) != 0);
> 
> maybe? Anyway, I'll let you decide on both, either way:
> 
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>

Did both and pushed. Thanks, a few of my machines were tripping over
this which is a bit puzzling as to how they have different values for
the stack warning.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre