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Date:   Mon, 11 Mar 2019 14:07:16 +0100
From:   Gerd Hoffmann <kraxel@redhat.com>
To:     Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc:     David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
        virtualization@lists.linux-foundation.org,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/bochs: Fix NULL dereference on atomic_disable helper
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  Hi,

> > >  static void bochs_crtc_atomic_flush(struct drm_crtc *crtc,
> > >  				    struct drm_crtc_state *old_crtc_state)
> > >  {
> > > @@ -66,6 +71,7 @@ static const struct drm_crtc_funcs bochs_crtc_funcs = {
> > >  static const struct drm_crtc_helper_funcs bochs_helper_funcs = {
> > >  	.mode_set_nofb = bochs_crtc_mode_set_nofb,
> > >  	.atomic_enable = bochs_crtc_atomic_enable,
> > > +	.atomic_disable = bochs_crtc_atomic_disable,
> > 
> > Shouldn't we make the callback optional instead of adding empty dummy
> > functions to drivers?
> 
> Hi Gerd,
> 
> I agree, and I can work in this issue.
> Just one question, should we make atomic_enable optional as well?

IIRC the drm code checks for the atomic_enable callback presence to
figure whenever it should take the atomic or legacy code paths.

So, I think that will not work.

cheers,
  Gerd