[Intel-gfx] [PATCH 2/2] drm/i915: Make use of intel_fb_obj()

[Daniel Vetter]

On Tue, Jul 08, 2014 at 07:47:13AM +0100, Chris Wilson wrote:
> On Mon, Jul 07, 2014 at 06:21:48PM -0700, Matt Roper wrote:
> > This should hopefully simplify the display code slightly and also
> > solves at least one mistake in intel_pipe_set_base() where
> > to_intel_framebuffer(fb)->obj is referenced during local variable
> > initialization, before 'if (!fb)' gets checked.
> > 
> > Potential uses of this macro were identified via the following
> > Coccinelle patch:
> > 
> >         @@
> >         expression E;
> >         @@
> >         * to_intel_framebuffer(E)->obj
> > 
> >         @@
> >         expression E;
> >         identifier I;
> >         @@
> >           I = to_intel_framebuffer(E);
> >           ...
> >         * I->obj
> > 
> > Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
> 
> The only drawback is that I am suddenly nervous of potential NULL
> objs...

I concur with Chris here, I think intel_fb_obj should be a static inline
and first check for fb == NULL. To catch abuse we could do an

if (WARN_ON(!fb))
	return NULL;

return to_intel_framebuffer(fb)->obj;

The most likely abuse is that we call intel_fb_obj before checking fb for
NULL, so the WARN is better than a BUG_ON. With that I don't think we need
to change the checks as Chris suggested here.
-Daniel

> 
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index 8c3dcdf..bc2519f 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -2356,7 +2356,7 @@ static void intel_find_plane_obj(struct intel_crtc *intel_crtc,
> >  	struct drm_device *dev = intel_crtc->base.dev;
> >  	struct drm_crtc *c;
> >  	struct intel_crtc *i;
> > -	struct intel_framebuffer *fb;
> > +	struct drm_i915_gem_object *obj;
> >  
> >  	if (!intel_crtc->base.primary->fb)
> >  		return;
> > @@ -2380,11 +2380,11 @@ static void intel_find_plane_obj(struct intel_crtc *intel_crtc,
> >  		if (!i->active || !c->primary->fb)
> >  			continue;
> >  
> > -		fb = to_intel_framebuffer(c->primary->fb);
> > -		if (i915_gem_obj_ggtt_offset(fb->obj) == plane_config->base) {
> > +		obj = intel_fb_obj(c->primary->fb);
> 
> I would move this before the c->primary->fb test and rewrite the check
> in terms of obj.
> 
> if (!i->active)
>   continue;
> 
> obj = intel_fb_obj(c->primary->fb);
> if (obj == NULL)
>   continue;
> 
> > +		if (i915_gem_obj_ggtt_offset(obj) == plane_config->base) {
> >  			drm_framebuffer_reference(c->primary->fb);
> >  			intel_crtc->base.primary->fb = c->primary->fb;
> > -			fb->obj->frontbuffer_bits |= INTEL_FRONTBUFFER_PRIMARY(intel_crtc->pipe);
> > +			obj->frontbuffer_bits |= INTEL_FRONTBUFFER_PRIMARY(intel_crtc->pipe);
> >  			break;
> >  		}
> >  	}
> >  
> 
> > @@ -9613,7 +9601,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
> >  
> >  	work->event = event;
> >  	work->crtc = crtc;
> > -	work->old_fb_obj = to_intel_framebuffer(old_fb)->obj;
> > +	work->old_fb_obj = intel_fb_obj(old_fb);
> >  	INIT_WORK(&work->work, intel_unpin_work_fn);
> 
> Here I would appreciate an
> if (WARN_ON(intel_fb_obj(old_fb) == NULL))
>   return -EBUSY;
> at the start of intel_crtc_page_flip.
> >  
> >  	ret = drm_crtc_vblank_get(crtc);
> 
> > @@ -12971,8 +12952,8 @@ void intel_modeset_gem_init(struct drm_device *dev)
> >  		if (!c->primary->fb)
> >  			continue;
> >  
> > -		fb = to_intel_framebuffer(c->primary->fb);
> > -		if (intel_pin_and_fence_fb_obj(dev, fb->obj, NULL)) {
> > +		obj = intel_fb_obj(c->primary->fb);
> 
> Same again, change the check on primary->fb to be a check on obj.
> 
> > +		if (intel_pin_and_fence_fb_obj(dev, obj, NULL)) {
> >  			DRM_ERROR("failed to pin boot fb on pipe %d\n",
> >  				  to_intel_crtc(c)->pipe);
> >  			drm_framebuffer_unreference(c->primary->fb);
> 
> Elsewhere a GPF for a NULL pointer is reasonable.
> -Chris
> 
> -- 
> Chris Wilson, Intel Open Source Technology Centre
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch