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Date:   Wed, 9 Jan 2019 12:37:24 +0100
From:   Boris Brezillon <bbrezillon@kernel.org>
To:     Daniel Vetter <daniel@ffwll.ch>
Cc:     Peter Rosin <peda@axentia.se>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        David Airlie <airlied@linux.ie>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>,
        Nicolas Ferre <nicolas.ferre@microchip.com>,
        Boris Brezillon <boris.brezillon@bootlin.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] drm/atmel-hlcdc: prevent divide by zero
Message-ID: <20190109123449.65742b99@bbrezillon>
In-Reply-To: <20190109101224.GT21184@phenom.ffwll.local>
References: <20190108123129.20031-1-peda@axentia.se>
        <20190109101224.GT21184@phenom.ffwll.local>
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On Wed, 9 Jan 2019 11:12:24 +0100
Daniel Vetter <daniel@ffwll.ch> wrote:

> On Tue, Jan 08, 2019 at 12:31:36PM +0000, Peter Rosin wrote:
> > While trying to temporarily hide a plane, one thing that was attempted
> > was to call (from libdrm)
> > 
> > 	drmModeSetPlane(fd, plane_id, crtc_id, fb_id, 0,
> > 			0, 0, 0, 0, 0, 0, 0, 0);
> > 
> > This call causes a pair of "Division by zero in kernel." messages. Kill
> > those messages, but preserve the current behaviour that also happen to
> > make the plane disappear with the above call.
> > 
> > Signed-off-by: Peter Rosin <peda@axentia.se>
> > ---
> >  drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_plane.c | 14 ++++++++++----
> >  1 file changed, 10 insertions(+), 4 deletions(-)
> > 
> > Side note, when comparing with drm_atomic_helper_check_plane_state(), I get
> > the feeling that the src rect should be clipped together with the crtc rect
> > if/when clipping is needed. That function calls drm_rect_clip_scaled(), and
> > the equivalent does not seem to happen here. Should clipping be performed
> > on the src rect?  
> 
> Any reasons atmel can't switch over to that helper? Would compute a nice
> ->visible state variable for you ...  

We should definitely use drm_atomic_helper_check_plane_state().